Late Roman army

Late Roman army

The Late Roman army is the term used to denote the military forces of the Roman Empire from the accession of Emperor Diocletian in 284 until the Empire's definitive division into Eastern and Western halves in 395. A few decades afterwards, the Western army disintegrated as the Western empire collapsed. The East Roman army, on the other hand, continued intact and essentially unchanged until its reorganization by themes and transformation into the Byzantine army in the 7th century. The term "late Roman army" is often used to include the East Roman army.

The army of the Principate underwent a significant transformation as a result of the chaotic 3rd century. Unlike the Principate army, the army of the 4th century was heavily dependent on conscription and its soldiers were more poorly remunerated than in the 2nd century. Barbarians from outside the empire probably supplied a much larger proportion of the late army's recruits than in the army of the 1st and 2nd centuries. There is no evidence, however, that barbarian recruitment damaged the army's effectiveness.

The army of the 4th century was probably no larger than that of the 2nd. The main change in structure was the establishment of large armies that accompanied the emperors ("comitatus praesentales") and were generally based away from the frontiers. Their primary function was to deter usurpations. The legions were split up into smaller units comparable in size to the auxiliary regiments of the Principate. In parallel, legionary armour and equipment were abandoned in favour of auxiliary equipment. Infantry adopted the more protective equipment of the Principate cavalry.

The role of cavalry in the late army does not appear to have been enhanced as compared with the army of the Principate. The evidence is that cavalry was much the same proportion of overall army numbers as in the 2nd century and that its tactical role and prestige remained similar. Indeed, the cavalry acquired a reputation for incompetence and cowardice for their role in three major battles in mid-4th century. In contrast, the infantry retained its traditional reputation for excellence.

The 3rd and 4th centuries saw the upgrading of many existing border forts to make them more defensible, as well as the construction of new forts with much higher defensive specifications. The interpretation of this trend has fuelled an ongoing debate whether the army adopted a defence-in-depth strategy or continued the same posture of "forward defence" as in the early Principate. Many elements of the late army's defence posture were similar to those associated with forward defence, such as forward location of forts, frequent cross-border operations, and external buffer-zones of allied barbarian tribes. Whatever the defence strategy, it was apparently less successful in preventing barbarian incursions than in the 1st and 2nd centuries. This may have been due to heavier barbarian pressure, and/or to the practice of keeping large armies of the best troops in the interior, depriving the border forces of sufficient support.


Much of our evidence for 4th century army unit deployments is contained in a single document, the "Notitia Dignitatum", compiled "ca." 395–420, a manual of all late Roman public offices, military and civil. The main deficiency with the "Notitia" is that it lacks any personnel figures so as to render estimates of army size impossible. Also, it was compiled at the very end of the 4th century; it is thus difficult to reconstruct the position earlier. However, the "Notitia" remains the central source on the late Army's structure due to the dearth of other evidence. [Lee (1997) 212]

The main literary sources for the 4th century army are the "Res Gestae" (History) of Ammianus Marcellinus, whose surviving books cover the period 353 to 378. Marcellinus, himself a veteran soldier, is regarded by scholars as a reliable and valuable source. But he largely fails to remedy the deficiencies of the "Notitia" as regards army and unit strength or units in existence, as he is rarely specific about either. The third major source for the late army is the corpus of imperial decrees published in the East Roman empire in the 5th and 6th centuries: the Theodosian code (438) and the Corpus Iuris Civilis (528–39). These compilations of Roman laws dating from the 4th century contain numerous imperial decrees relating to all aspects of the regulation and administration of the late army.

"De re militari", a treatise on Roman military affairs by Vegetius, a late 4th century writer, contains considerable information on the late army, although its focus is on the army of the Republic and Principate. However, Vegetius (who wholly lacked military experience) is often unreliable. For example, he stated that the army abandoned armour and helmets in the later 4th century (offering the absurd explanation that this equipment was too heavy), which is contradicted by sculptural and artistic evidence. [Elton (1996) 110-5] In general, it is not safe to accept a Vegetius statement unless it is corroborated by other evidence.

Scholars of the late army have to contend with a dramatic diminution of the epigraphic record in the 3rd and 4th centuries, compared with the 1st–2nd centuries. Diplomas were no longer issued to retiring auxiliaries after 203 (most likely because almost all were already Roman citizens by then). In addition, there was a huge reduction in the number of tombstones, altars and other dedications by Roman servicemen. Official stamps of military units on building materials ("e.g." tiles) are much rarer. But this trend should probably not be seen as indicating a decline in the army's administrative sophistication. Papyrus evidence from Egypt shows that military units continued to keep detailed written records in the 4th century (the vast bulk of which are lost due to organic decomposition). Most likely, the decline in inscriptions is due to changing fashion, in part influenced by the increase in barbarian recruits and the rise of Christianity. [Mattingly (2006) 247-8] The dearth of inscriptions leaves major gaps in our understanding of the late army and renders many conclusions tentative.

Evolution of the 4th century army

Background: the Principate army

The regular army of the Principate was established by the founder–emperor Augustus (ruled 30 BC – 14 AD) and survived until the end of the 3rd century. The regular army consisted of two distinct corps, both being made up of mainly volunteer professionals.

The elite legions were large infantry formations, varying between 25 and 33 in number, of ca. 5,500 men each (all infantry save a small cavalry arm of 120) which admitted only Roman citizens. [Goldsworthy (2003) 50, 78] The "auxilia" consisted of around 400 much smaller units of ca. 500 men each (a minority were up to 1,000 strong), which were divided into approximately 100 cavalry "alae", 100 infantry "cohortes" and 200 mixed cavalry/infantry units or "cohortes equitatae". [Holder (2003) 120] Some auxilia regiments were designated "sagittariorum", meaning that they specialised in archery. The "auxilia" thus contained almost all the Roman army's cavalry and archers, as well as (from the late 1st century onwards) approximately the same number of foot soldiers as the legions. [Goldsworthy (2003) 56–8] The "auxilia" were mainly recruited from the "peregrini": provincial subjects of the empire who did not hold Roman citizenship, but the "auxilia" also admitted Roman citizens and possibly "barbari", the Roman term for peoples living outside the empire's borders. [Goldsworthy (2003) 80] At this time both legions and auxilia were almost all based in frontier provinces. [Holder (2003) 145] The only substantial military force at the immediate disposal of the emperor was the elite Praetorian Guard of 10,000 men which was based in Rome. [Goldsworthy (2003) 58]

The senior officers of the army were, until the 3rd century, mainly from the Italian aristocracy. Members of the senatorial order, the highest echelon, exclusively filled the following posts::(a) "legatus Augusti" (provincial governor, who commanded military forces in the province as well as heading the civil administration):(b) "legatus legionis" (legion commander):(c) "tribunus militum laticlavius" (legion deputy commander). [Goldsworthy (2003) 60]

The "equites" (or "knights"), the second order of nobility, provided::(a) the governors of Egypt and a few minor provinces:(b) the two "praefecti praetorio" (commanders of the Praetorian Guard):(c) a legion's "praefectus castrorum" (3rd-in-command) and its remaining five "tribuni militum" (senior staff officers):(d) the "praefecti" (commanders) of the auxiliary regiments. [Goldsworthy (2003) 64–5]

Although the two aristocratic orders were hereditary, they were not closed to outsiders. Commoners could be elevated to equestrian rank, and "equites" to senatorial rank, by decree of the emperor, issued in his capacity as Roman censor. Elevation was usually granted only to those who met the minimum property qualification for each order, which was set by Augustus at 250,000 "denarii" for senators and at 100,000 "denarii" for "equites" (For comparison, a 1st century legionary's gross pay was 250 "denarii" per annum). Apart from the higher property requirement, it was far more difficult for a family to enter the senatorial order because the head of the family needed first to win a seat in the Senate itself, whose membership was limited to 600 life peers and where, as a consequence, only a few vacancies became available each year. "Equites", whose numbers were unrestricted, thus greatly outnumbered senatorians. Already wealthy to start with, the aristocracy accumulated even greater riches by their monopoly of the senior posts in the administration, which carried enormous salaries (and also opportunities for peculation). For example, the senatorial governor of Africa Proconsularis province was paid 250,000 "denarii", the same "each year" as the entire property qualification for his order, whilst the "praefectus" of an auxiliary cohort was paid ca. 50 times as much as a common foot soldier. [Jones (1964) 31] [Birley (1988) ] Senatorians were prohibited from engaging in commerce, which was considered beneath their status, and therefore invested all their wealth in land. Vast land portfolios, often spread across multiple provinces of the empire, were established. For example, in the time of emperor Nero (54-68), half of the cultivable land of Africa province, then among the most productive agriculturally, was owned by just six senators. [Thompson (1987) 556] "Equites", who were unrestricted, invested not only in land, but also in commercial enterprises: tax collection, shipping and overland transport, mines, construction and manufacturing industry. The Roman aristocracy thus monopolised political, military and economic power.

Hereditary senators and "equites" normally combined military service with civilian posts, a career path known as the "cursus honorum", typically starting with a period of junior administrative posts in Rome, followed by 5–10 years in the military and a final period of senior positions in the either the provinces or Rome. [Goldsworthy (2003) 60, 66] This tightly-knit ruling oligarchy achieved a remarkable degree of political stability. During the first 200 years of its existence (30 BC - 180 AD), the empire suffered only one major episode of civil strife (the Civil War of 68-9). Otherwise, usurpation attempts by provincial governors were very few and swiftly suppressed.

But already by the late 1st century, an alternative aristocracy, non-Italian and military, was becoming established. This was a result of the practice whereby the emperor customarily elevated the "primuspilus" (chief centurion) of each legion to equestrian rank on completion of his year in office. This resulted in some 30 career soldiers, mostly non-Italian and risen from the ranks, joining the aristocracy each year. [Goldsworthy (2003) 65–6]

3rd century developments

The seminal development for the army in the early 3rd century was the "Constitutio Antoniniana" (Antonine Decree) of 212, issued by Emperor Caracalla (ruled 211–18). This granted Roman citizenship to all free inhabitants of the empire, ending the second-class status of the "peregrini". [The Roman Law Library "Constitutio Antoniniana de Civitate"] This had the effect of breaking down the distinction between the citizen legions and the auxiliary regiments. In the 1st and 2nd centuries, the legions were the symbol (and guarantors) of the dominance of the Italian "master nation" over its subject peoples. In the 3rd century, they were no longer socially superior to their auxiliary counterparts (although they may have retained their elite status in military terms) and the legions' special armour and equipment ("e.g." the "lorica segmentata") was phased out. [Goldsworthy (2003) 205]

The traditional alternation between senior civilian and military posts fell into disuse in the 2nd and 3rd centuries, as the Italian hereditary aristocracy was progressively replaced in the senior echelons of the army by the "primipilares" (former chief centurions). [Goldsworthy (2000) 164–65] In the 3rd century, only 10% of auxiliary prefects whose origins are known were Italian equestrians, compared to the majority in the previous two centuries. [Holder (1982) 65] At the same time, equestrians increasingly replaced the senatorial order in the top commands. Septimius Severus (ruled 197–211) placed equestrian "primipilares" in command of the three new legions he raised and Gallienus (260–68) did the same for all the other legions, giving them the title "praefectus pro legato" ("prefect acting as legate"). [Goldsworthy (2000) 164] [Tomlin (1988) 108] The rise of the "primipilares" may have provided the army with more professional leadership, but it resulted in a major increase in military rebellions by ambitious generals seeking supreme power. The 3rd century saw numerous "coups d'etat" and destructive civil wars. Few 3rd century emperors enjoyed long reigns or died of natural causes. [Goldsworthy (2000) 164-5]

Emperors responded to the increased insecurity with a steady build-up of the forces at their immediate disposal. These became known as the "comitatus" ("escort", from which derives the English word "committee"). To the Praetorian Guard's 10,000 men, Septimius Severus added the legion "II Parthica". Based at Albano Laziale near Rome, it was the first legion to be stationed in Italy since Augustus. In addition, he doubled the size of the imperial escort cavalry, the "equites singulares Augusti", to 2,000 by drawing select detachments from "alae" on the borders. [Tomlin (1988) 107] In total, his "comitatus" numbered some 17,000 men, equivalent to 31 infantry "cohortes" and 11 "alae" of cavalry. The trend for the emperor to gather round his person ever greater forces reached its peak in the 4th century under Constantine I the Great (ruled 312–37), whose "comitatus" may have reached 100,000 men, perhaps a quarter of the army's total effective strength. [Zosimus II.43]

The rule of Gallienus saw the appointment of a senior officer, with the title of "dux" (plural form: "duces", the origin of the medieval noble rank of duke), to command all the "comitatus" cavalry. This force included some contingents of "equites promoti" (cavalry contingents detached from the legions), plus some apparently new Dalmatian light cavalry ("equites Dalmatarum") and elements of allied barbarian cavalry ("equites foederati"). [Tomlin (1988) 108] Under Constantine I, the head of the "comitatus" cavalry was given the title of "magister equitum" ("master of horse"), which in Republican times had been held by the deputy to a Roman dictator. [Jones (1964) 97] But neither title implies the existence of an independent "cavalry army", as was suggested by some more dated scholars. The cavalry under both officers were integral to mixed infantry and cavalry "comitatus", with the infantry remaining the predominant element.Goldsworthy (2000) 170]

The 3rd century saw a progressive reduction in the size of the legions and even some auxiliary units. Legions were broken up into smaller units, as evidenced by the shrinkage and eventual abandonment of their traditional large bases, in Britain for example. [Mattingly (2006) 244] In addition, from the 2nd century onwards, the separation of some detachments from their parent units became permanent in some cases, establishing new unit types, "e.g." the "vexillatio equitum Illyricorum" based in Dacia in the early 2nd century [Holder (2003) 133] and the "equites promoti" [Tomlin (1988) 108] and "numerus Hnaufridi" in Britain. [Mattingly (2006) 223] This led to the proliferation of unit types in the 4th century, generally of smaller size than those of the Principate. For example, in the 2nd century, "vexillatio" (from "vexillum" = "standard") was originally a generic term meaning any detachment from a legion or auxiliary regiment, either cavalry or infantry. In the 4th century, it denoted an elite cavalry regiment. [Goldsworthy (2000) 219]

In the 3rd century, a small number of regular units are recorded as bearing the names of barbarian tribes (as opposed to "peregrini" tribal names) for the first time. These were clearly "foederati" (allied troops under a military obligation to Rome) converted into regular units, a trend that was to accelerate in the 4th century. [Jones (1964) 620] The "ala I Sarmatarum", for example, based in Britain, was probably composed of some of the 5,500 captured Sarmatian horsemen sent to garrison Hadrian's Wall by emperor Marcus Aurelius in "ca." 175. [Dio Cassius LXXI ] There is no evidence of irregular barbarian units becoming part of the regular Principate army until the 3rd century. [Holder (1980) 109–24]

3rd century crisis

The mid-3rd century saw the empire plunged into a military and economic crisis which almost resulted in its disintegration. It consisted of a series of military catastrophes in 251–271 when Gaul, the Alpine regions and Italy, the Balkans and the East were simultaneously overrun by Alamanni, Sarmatians, Goths and Persians respectively. [Jones (1964)25] At the same time, the Roman army was struggling with the effects of a devastating pandemic, probably of smallpox, the Plague of Cyprian which began in 251 and was still raging in 270, when it claimed the life of Emperor Claudius II Gothicus (268–70). [Zosimus I.24] The evidence for the earlier Antonine pandemic of the late 2nd century, also smallpox, indicates a mortality of 15–30% in the empire as a whole. [D. Ch. Stathakopoulos "Famine and Pestilence in the late Roman and early Byzantine Empire" (2007) 95] Zosimus describes the Cyprianic outbreak as even worse. [Zosimus I.16] The armies would likely have suffered deaths at the top end of the range, due to their close concentration of individuals and frequent movements across the empire. [Zosimus I.20]

The 3rd century crisis started a chain-reaction of socio-economic effects that proved decisive for the development of the late army. The combination of barbarian devastation and reduced tax-base due to plague bankrupted the imperial government, which resorted to issuing ever more debased coin "e.g." the "antoninianus", the silver coin used to pay the troops in this period, lost 95% of its silver content between its launch in 215 and its demise in the 260s. [J. Kent "The Monetary System" in Wacher (1988) 576–7.] (In other words, by the end of the period, the government was able to issue 20 times the quantity of "antoniniani" with the same amount of precious metal). This inevitably led to rampant price inflation. For example, the price of wheat under Diocletian was 67 times the typical Principate figure. [Duncan-Jones (1990) 115] The monetary economy collapsed and the army was obliged to rely on unpaid food levies to obtain sufficient supplies. [Tomlin (1988) 110] Food levies were raised when and where required, without regard to fairness, ruining the border provinces where the military was mainly based. [Jones (1964) 32] Soldiers' salaries became virtually worthless, reducing the army's recruits, once well-paid with plenty of disposable income, to a subsistence-level existence little better than that endured by their peasant families. [Jones (1964) 29] This in turn discouraged volunteers and forced the government to rely on conscription to find enough recruits. [Jones (1964) 615] But even this was not sufficient to plug the recruitment shortfalls caused by the plague. The only solution was large-scale recruitment of barbarians into the regular army. By the mid-4th century, barbarian-born men probably accounted for about a quarter of all recruits (and over a third in elite regiments), likely a far higher share than in the 1st–2nd centuries. [Elton (1996) 148–52]

Illyrian military junta

The Illyrian-speaking tribes that dominated the Roman provinces of Pannonia, Dalmatia and Moesia Superior, and included mountain tribes of semi-nomadic pastoralists such as the Dalmatae and Breuci, had a fearsome reputation as warriors. [N. G. L. Hammond "The Illyrians and NW Greeks" in Cambridge Ancient History Vol VI (1994) 428] They were seen as excellent soldier material. From the time of Domitian (ruled 81–96), when over half the Roman army was deployed in the Danubian regions, the Illyrian provinces became the most important recruiting ground of the auxilia and later the legions.Tomlin (1988) 109] In the 3rd century, Romanised Illyrians, mostly "primipilares" and their descendants, came to dominate the army's senior officer echelons. [Goldsworthy (2000) 165]

Finally, the Illyrian officer class seized control of the state itself. In 268, the emperor Gallienus (ruled 260–68) was overthrown by a "coup d'état" organised by a clique of Illyrian senior officers, including his successors Claudius II Gothicus and Aurelian (270–75). [Zosimus I.22] They and their successors Probus (276–78) and Diocletian (ruled 284–305) and his colleagues in the Tetrarchy formed a sort of self-perpetuating military junta of Illyrian officers who were born in the same provinces (several in the same city, Sirmium, a major legionary base in Moesia Superior) or had served in the same regiments.

The junta succeeded in reversing the military disasters of 251–71 with a string of brilliant victories, most notably the defeat inflicted at Naissus on a vast Gothic army by Claudius II, which was so crushing that the Goths did not seriously threaten the empire again until a century later at Adrianople (378). [Zosimus I.23]

The Illyrian emperors continued to rule the empire until 379. Indeed, until 363, power was held by descendants of one of the original junta members. Constantine I' s father, Constantius Chlorus was a "Caesar" (deputy emperor) in Diocletian's Tetrarchy. [Zosimus II.40] His grandson Julian ruled until 363. The Illyrian emperors restored the army to its former strength and effectiveness. But they had a narrow political focus, solely concerned with the needs and interests of the military. They were also divorced from the immensely wealthy Roman senatorial families that continued to dominate the Senate and owned much of the empire's land. This in turn bred a feeling of alienation from the army among the Roman aristocracy which in the later 4th century began to resist the military's exorbitant demands for recruits and supplies. [Lee (1997) 221 (note 58)]


Diocletian's wide-ranging administrative, economic and military reforms were entirely aimed at providing the military with sufficient resources, both in manpower and supplies. [Luttwak (1977) 177] In the words of one historian, "Diocletian ... turned the entire empire into a regimented logistic base" (to supply the army). [Luttwak (1976) 177]

To this end, Diocletian instituted the system of "indictiones" (tax demands issued in advance of the tax cycle), with the amount of tax demanded related to the amount of cultivated land in each province, aimed at making more efficient and more equitable the collection of taxes in kind. To deal with the problem of rural depopulation (and consequent loss of food production), he decreed that peasants must register in their home locality and never leave it. [Jones (1964)]

To ensure the army received sufficient recruits, Diocletian appears to have instituted systematic annual conscription for the first time since the days of the Roman Republic. In addition he is probably responsible for the decree, first recorded in 313, obliging the sons of serving soldiers (and officers) or veterans to enlist. [Jones (1964) 615]

Under Diocletian, the number of legions, and probably of other units, appears to have more than doubled. [Jones (1964) 17] But it is unlikely that overall army size increased nearly as much, since unit strengths appear to have been reduced, in some cases drastically. [Duncan-Jones (1990) 117] [Tomlin (1988) 111] Even so, it is generally agreed that Diocletian increased army numbers substantially. But this was probably from a much lower base than its Severan peak of ca. 440,000, as the army presumably shrank sharply as a result of plague and military disasters in the late 3rd century. [MacMullen (1979) 455] The evidence is that Diocletian restored its strength to at least that of the early 2nd century (ca. 390,000). [John Lydus "De Mensibus" I.47] But even more than restoring the size of the army, Diocletian's efforts and resources were focused on a massive upgrading of the defensive infrastructure along all the empire's borders, including new forts and strategic military roads. [Jones (1964) 55-6]

Diocletian and his three colleagues each had a "comitatus" at their disposal. But under Diocletian, these remained informal and small in size and relied on reinforcements from frontier forces for major operations. [Jones (1964) 608] Nevertheless, added together, they must have constituted a significant force.

Diocletian's administrative reforms had the twin aims of ensuring political stability and providing the bureaucratic infrastructure needed to raise the recruits and supplies needed by the army.

At the top, Diocletian instituted the Tetrarchy. This divided the empire into two halves, East and West, each to be ruled by an "Augustus" (emperor); each "Augustus" would in turn appoint a deputy called a "Caesar", who would act both as his second-in-command and designated successor. This four-man team would thus have the flexibility to deal with multiple and simultaneous challenges, while also providing a legitimate succession. [Goldsworthy (2000) 166]

Diocletian reformed the provincial administration, establishing a three-tiered provincial hierarchy, in place of the previous single-tier structure. The original 42 Principate provinces were almost tripled in number to "ca." 120. These were grouped into 12 divisions called dioceses, each under a "vicarius", in turn grouped into four praetorian prefectures, to correspond to the areas of command assigned to the four Tetrarchs, who were each assisted by a "praefectus praetorio" (not be confused with the commanders of the Praetorian Guard). The aim of this fragmentation of provincial administration was probably to reduce the possibility of military rebellion by governors (by reducing the forces they each controlled). [Jones (1964) 608]

Also to this end, Diocletian divorced military from civil command in some cases. The old "legatus Augusti" (governor) of the Principate had combined the role of administrative head with that of commander-in-chief of forces in his province. Now, command of troops in some provinces was entrusted to purely military officers called "duces limitis" ("border commanders"). However, this was not universally applied. In many provinces, the governor remained in command. In any case, both "duces" and governors continued to be commanded by their "vicarius" and "praefectus praetorio". [Jones (1964) 608] Diocletian completed the exclusion of the senatorial class, still dominated by the Italian aristocracy, from all senior military commands and all top administrative posts except in Italy. [Jones (1964) 50]

Ironically, Diocletian's administrative reforms may have worked against the army's best interests by entrenching a largely conscript army. The reforms led to explosive growth in the size of the imperial bureaucracy. The Principate had been a remarkably slimline administration, with just 250 senior officials running the vast empire, relying on local government and private contractors to deliver the necessary taxes and services. By the time of the "Notitia", comparable positions had grown to "ca." 6,000, a 24-fold increase. [Heather (2005) 228] Admittedly, late high officials were paid far less than in the Principate, perhaps an average of a tenth as much. [Jones (1964) 31] Nevertheless, the late bureaucracy would still have been around two and a half times as expensive overall, swallowing resources which would probably have been sufficient to bring soldiers' pay back to 2nd-century levels. [cf. Duncan-Jones (1994) ] The lower pay of the 4th century obliged the army to rely on often reluctant or poor-quality conscripts rather than attracting better-grade volunteers as in the Principate.


Constantine I probably completed the replacement of provincial governors as commanders of military units in their provinces by "duces". The "praefecti praetorio" lost their military command and became purely administrative officials, whose central and vital role was to ensure that the armies in their circumscription were properly supplied. [Jones (1964) 606, 627]

After defeating Maxentius in 312, Constantine disbanded the Praetorian Guard, ending the latter's 300-year existence. [Jones (1964) 100] Although the instant reason was the Guard's support for his rival Maxentius, a force based in Rome had also become obsolete since emperors now rarely resided there. The imperial escort role of the Guard's cavalry, the "equites singulares Augusti", was now fulfilled by the "scholae". These elite cavalry regiments existed by the time of Constantine and may have been founded by Diocletian. [Jones (1964) 613]

Constantine expanded his "comitatus" into a major and permanent force. This was achieved by the addition of units withdrawn from the frontier provinces and by creating new units: more cavalry "vexillationes" and new-style infantry units called "auxilia". The expanded "comitatus" was now placed under the command of two new officers, a "magister peditum" to command the infantry and "magister equitum" for cavalry (after Constantine's death, these titles became interchangeable, with both officers commanding mixed infantry/cavalry forces). "Comitatus" troops were now formally denoted "comitatenses" to distinguish them from the frontier forces ("limitanei"). [Jones (1964) 608] The size of the Constantinian "comitatus" is uncertain. But Constantine mobilised 98,000 troops for his war against Maxentius, according to Zosimus. [Zosimus II.43] It is likely that most of these were retained for his "comitatus". [Jones (1964) 97] This represented about a quarter of the total regular forces, if one accepts that the Constantinian army numbered around 400,000. [Elton (1996) 120] The rationale for such a large "comitatus" has been debated among scholars. A traditional view sees the "comitatus" as a strategic reserve which could be deployed against major barbarian invasions that succeeded in penetrating deep into the empire or as the core of large expeditionary forces sent across the borders. But more recent scholarship has viewed its primary function as insurance against potential usurpers. [Goldsworthy (2000) 170] (See Strategy below).

In addition, Constantine appears to have reorganised the border forces along the Danube, replacing the old-style "alae" and "cohortes" with new units of "cunei" (cavalry) and "auxilia" (infantry) respectively. [Jones (1964) 608] It is unclear how the new-style units differed from the old-style ones, but those stationed on the border (as opposed to those in the "comitatus") may have been smaller, perhaps half the size. [Mattingly (2006) 239] In sectors other than the Danube, old-style auxiliary regiments survived. [Jones (1964) 58]

The 5th-century historian Zosimus strongly criticised the establishment of the large "comitatus", accusing Constantine of wrecking his predecessor Diocletian's work of strengthening the border defences: "By the foresight of Diocletian, the frontiers of the Roman empire were everywhere studded with cities and forts and towers... and the whole army was stationed along them, so it was impossible for the barbarians to break through... But Constantine ruined this defensive system by withdrawing the majority of the troops from the frontiers and stationing them in cities which did not require protection." [Zosimus II.54–5 (Translation in Jones (1964) 52)]

Zosimus' critique is probably excessive, both because the "comitatus" already existed in Diocletian's time and because some new regiments were raised by Constantine for his expanded "comitatus", as well as incorporating existing units. [Jones (1964) 52] Nevertheless, the majority of his "comitatus" was drawn from existing frontier units. [Tomlin (1988) 111] This drawdown of large numbers of the best units inevitably increased the risk of successful large-scale barbarian breaches of the frontier defences. [Luttwak (1976) 179]

It was probably this factor that led to the emergence of "comitatus" based in frontier regions (the regional "comitatus"), distinct from the "comitatus praesentales" escorting the emperor(s). From the defeat of the usurper Magnentius in 353, there appears to have always been a "comitatus" in Gaul and one in the East, each under a "magister equitum", and one in Illyricum under a senior "comes (rei militaris)" (plural form: "comites", literally "companion (for military affairs)", the origin of the medieval noble rank of "count"), irrespective of where the emperor(s) were. [Jones (1964) 125] These regional armies became steadily more numerous until, by the time of the "Notitia", there were three in the East and six in the West. [Jones (1964) 608] Their evolution was a partial reversal of Constantine's policy and, in effect, a vindication of Zosimus' critique that the "limitanei" forces had been left with insufficient support. [Lee (1997) 216] But the imperial escort armies remained in existence, and in "ca." 420 the three "comitatus praesentales" listed in the "Notitia", each 20–30,000 strong, still contained a total of "ca." 75,000 men. [Treadgold (1995) 45] If one accepts that the army at the time numbered about 350,000 men, the escort armies still contained 20–25% of the total effectives.

Regiments which remained with the escort armies were, not later than 365, denoted "palatini" (lit. "of the palace", from "palatium"), a higher grade of "comitatenses". [Jones (1964) 125] Regiments were now classified in four grades, which denoted quality, prestige and probably pay. These were, in descending order, "scholares", "palatini", "comitatenses" and "limitanei". [Elton (1996) 94-5]

Army size

The traditional view of scholars is that the 4th century army was much larger than the 2nd century army, in the region of double the size. The late 6th century writer Agathias, gives a global total of 645,000 effectives for the army "in the old days", presumed to mean at its peak under Constantine I. [Agathias "History" V.13.7–8; Jones (1964) 680] This figure probably includes fleets, giving a total of ca. 600,000 for the army alone. A.H.M. Jones' "Later Roman Empire" (1964), which contains the fundamental study of the late Roman army, calculated a similar total of 600,000 (exc. fleets) by applying his own estimates of unit strength to the units listed in the "Notitia Dignitatum". [Jones (1964) 683]

But the Agathias-Jones view has fallen out of favour with some historians in more recent times. Agathias' figure, if it has any validity at all, probably represents the official, as opposed to actual strength of the Constantinian army. In reality, the slim evidence is that late units were often severely under-strength, perhaps only about two-thirds of official. [Elton (1996) 89] Thus Agathias' 600,000 on paper may not have been more than ca. 400,000 in reality. The latter figure accords well with the other global figure from ancient sources, that of the 6th century writer John Lydus of 389,704 (excluding fleets) for the army of Diocletian. Lydus' figure is accorded greater credibility than Agathias' by scholars because of its precision (implying that it was found in an official document) and the fact that it is ascribed to a specific time period. [Heather (1995) 63]

Jones' figure of 600,000 is based on assumptions about unit strengths which may be too high. This especially concerns "limitanei" units (there is less dispute about the size of "comitatus" units, for which there is more available evidence). Jones calculated unit strengths in Egypt under Diocletian using papyrus evidence of unit payrolls. But a rigorous reassessment of the evidence by R. Duncan-Jones concluded that Jones had overestimated unit sizes by 2–6 times. [Duncan-Jones (1990) 105–17] For example, Jones estimated legions on the frontiers at ca. 3,000 men. [Jones (1964) 681-2] But Duncan-Jones' revisions found frontier legions of around 500 men, an "ala" of just 160 and an "equites" unit of 80. Even allowing for the possibility that some of these units were simply detachments from larger units, it is likely that Diocletianic unit strengths were far lower than earlier. [Duncan-Jones (1990) 117]

Duncan-Jones' figures receive support from a substantial corpus of excavation evidence from all the imperial borders which suggests that late forts were designed to accomodate much smaller garrisons than their Principate predecessors. Where such sites can be identified with forts listed in the "Notitia", the implication is that the resident units were also smaller. Examples include the "Legio II Herculia", created by Diocletian, which occupied a fort just one-seventh the size of a typical Principate legionary base, implying a strength of ca. 750 men. At "Abusina" on the Rhine, the "Cohors III Brittonum" was housed in a fort only 10% the size of its old Trajanic fort, suggesting that it numbered only around 50 men. The evidence must be treated with caution as identification with "Notitia" sites is often tentative and again, the units in question may be detachments (the "Notitia" frequently shows the same unit in two or three different locations simultaneously). Nevertheless, the weight of the evidence favours small sizes for frontier units. [Coello (1996) 51]

At the same time, more recent work has suggested that the regular army of the 2nd century was considerably larger than the ca. 300,000 traditionally assumed. This is because the 2nd century auxilia were not just equal in numbers to the legions as in the early 1st century, but some 50% larger. [Holder (2003) 120] The Principate army probably reached a peak of nearly 450,000 (excluding fleets and "foederati") at the end of the 2nd century. [MacMullen (1979) 454] Furthermore, the evidence is that the actual strength of 2nd century units was typically much closer to official (ca. 85%). [Goldsworthy (2003) 144–5] In any case, estimates of army strength for the Principate are based on much firmer evidence than those for the later period, which are highly speculative, as the table below shows.

NOTE: Ranks correspond only in pay scale, not necessarily in function

Senior officers

A significant innovation of the 4th century was the corps of "protectores", which contained cadet senior officers. Although "protectores" were supposed to be soldiers who had risen through the ranks by meritorious service, it became a widespread practice to admit to the corps young men from outside the army (often the sons of senior officers). The "protectores" formed a corps that was both an officer training school and pool of staff officers available to carry out special tasks for the "magistri militum" or the emperor. Those attached to the emperor were known as "protectores domestici" and organised in four "scholae" under a "comes domesticorum". After a few years' service in the corps, a "protector" would normally be granted a commission ("sacra epistula") by the emperor and placed in command of a military regiment. [Jones (1964) 636–40]

Regimental commanders were known by one of three possible titles: "tribunus" (for "comitatus" regiments plus border "cohortes"), "praefectus" (most other "limitanei" regiments) or "praepositus" (for "milites" and some ethnic units). [Jones (1964) 640] [Elton (1996) 101] Although most "tribuni" were appointed from the corps of "protectores", a minority were directly commissioned outsiders. [Jones (1964) 642] The status of regimental commanders varied enormously depending on the grade of their unit. At the top end, the commanders of "scholae" were, by the early 5th century granted the higher rank of "comes".

Between regimental and corps command were a group of senior staff officers who carried the title of "comes", but were junior to the "comites rei militaris" who commanded the regional "comitatus". They included the commanders of "scholae" who had been granted this title, as well as "pure" staff officers (i.e. without a command) who accompanied the emperor or a "magister militum". [Jones (1964) 641] In addition, it appears that the commander of a brigade of two twinned "comitatus" regiments was called a "comes". (Such twinned regiments would always operate and transfer together e.g. the legions "Ioviani" and "Herculiani"). [Elton (1996) 91]

It is unknown what proportion of the corps commanders ("duces", "comites" and "magistri militum") had risen from the ranks, but it is likely to have been small as progress through the junior ranks to "protector" was often by seniority and very slow. Most rankers would therefore be nearing retirement age by the time they were given command of a regiment and would go no further. [Tomlin (1988) 115] Ammianus names four rankers who reached above "tribunus". [Jones (1964) 643] One, the "comes" Flavius Memorius, served 28 years (i.e. was probably nearly 50) before joining the "protectores". In contrast, directly commissioned "protectores" and "tribuni" dominated the higher echelons, as they were usually young men when they started. For such men, promotion to corps command could be swift e.g. Theodosius I was a "dux" at age 28. [Jones (1964) 639] It was also possible for rungs on the rank ladder to be skipped. Commanders of "scholae", who enjoyed direct access to the emperor, often reached the highest rank of "magister militum". The barbarian-born Agilo was promoted direct to "magister militum" from "tribunus" of a "schola" in 360. [Jones (1964) 641]


The basic equipment of a 4th century foot soldier was essentially the same as in the 2nd century: metal armour cuirass, metal helmet, shield and sword. Some evolution took place during the 3rd century. Trends included the adoption of warmer clothing; the disappearance of distinctive legionary armour and weapons; the adoption by the infantry of equipment used by the cavalry in the earlier period; and the greater use of heavily armoured cavalry called cataphracts. [Elton (1996) ]


In the 1st and 2nd centuries, a Roman soldier's clothes consisted of a single-piece, short-sleeved tunic whose hem reached the knees and special hobnailed sandals ("caligae"). This attire, which left the arms and legs bare, had evolved in a Mediterranean climate and was not suitable for northern Europe in cold weather. In northern Europe, long-sleeved tunics, trousers ("bracae"), socks (worn inside the "caligae") and laced boots were commonly worn in winter from the 1st century. During the 3rd century, these items of clothing became much more widespread, apparently common in Mediterranean provinces also. [Goldsworthy (2003) 120, 127] However, it is likely that in warmer weather, trousers were dispensed with and "caligae" worn instead of socks and boots. [Mosaic from Piazza Armerina]


Legionary soldiers of the 1st and 2nd centuries had exclusive use of the "lorica segmentata" or laminated-strip cuirass which was a complex piece of armour which provided superior protection to the other types of Roman armour, chain mail ("lorica hamata") and scale armour ("lorica squamata"). Testing of modern replicas have demonstrated that this kind of armour was impenetrable to most direct and missile strikes. It was, however, uncomfortable: reenactors have discovered that chafing renders it painful to wear for longer than a few hours at a time. It was also expensive to produce and difficult to maintain. [Goldsworthy (2003) 129] In the 3rd century, the "segmentata" appears to have been dropped and troops are depicted wearing chain mail (mainly) or scales, the standard armour of the 2nd century auxilia. The artistic record shows that most late soldiers wore metal armour, despite Vegetius' statement to the contrary. For example, illustrations in the "Notitia" show that the army's "fabricae" (arms factories) were producing mail armour at the end of the 4th century. ["Notitia" Oriens.XI] Actual examples of both scale armour and quite large sections of mail have been recovered, at Trier and Weiler-La-Tour respectively, within fourth century contexts. [Bishop and Coulston (2006) 208] Officers generally seem to have worn bronze or iron cuirasses, as in the days of the Principate, together with traditional "pteruges". [Elton (1996) 111] The cataphract and "clibanarii" cavalry, from limited pictorial evidence and especially from the description of these troops by Ammianus, seem to have worn specialist forms of armour. In particular their limbs were protected by laminated defences, made up of curved and overlapping metal segments. [Ammianus, XVI 10]


In general, Roman cavalry helmets had enhanced protection, in the form of wider cheek-guards and deeper neck-guards, for the sides and back of the head than infantry helmets. Infantry were less vulnerable in those parts due to their tighter formation when fighting. [Goldsworthy (2003) 137] During the 3rd century, infantry helmets tended to adopt the more protective features of Principate cavalry helmets. Cheek-guards could often be fastened together over the chin to protect the face, and covered the ears save for a slit to permit hearing e.g. the "Auxiliary E" type or its Niederbieber variant. Cavalry helmets became even more enclosed e.g. the "Heddernheim" type, which is close to the medieval great helm, but at the cost much reduced vision and hearing. [Goldsworthy (2003) 126]

In contrast, some infantry helmets in the 4th century reverted to the more open features of the main Principate type, the "Imperial Gallic". The "Intercisa" design left the face unobstructed and had ear-holes in the join between cheek-guards and bowl to allow good hearing. In a radical change from the earlier single-bowl design, the Intercisa bowl was made of two separate pieces joined by a riveted ridge in the middle (hence the term "ridge helmet"). It was simpler and cheaper to manufacture, and therefore probably by far the most common type, but structurally weaker and therefore offered less effective protection. [Goldsworthy (2003) 123, 126] A more protective ridge helmet, with nose-guard and ear-holes, was the "Burgh Castle" type (with ear-holes) and its Conceşti variant, which is probably the cavalry version, as it lacks ear-holes. Reenactors are fond of portraying late soldiers wearing helmets with nose-guards, but it is unclear how common these were, as they are never depicted in images and bas-reliefs such as those on the Arch of Constantine. Face-guards of mail or in the form of metal 'anthropomorphic masks,' with eye-holes, were often added to the helmets of the heaviest forms of cavalry, especially "cataphracti". [Goldsworthy (2003) 123, 205]

Despite the apparent cheapness of manufacture of their basic components, many surviving examples of Late Roman helmets, including the Intercisa type, show evidence of expensive decoration in the form of silver or silver-gilt sheathing. [Southern & Dixon (1996) 92-93] [ Bishop & Coulston (2006) 210-213] A possible explanation is that most of the surviving exemplars may have belonged to officers and that silver- or gold-plating denoted rank; and, in the case of mounted gemstones, high rank e.g. the ornate Deurne helmet, believed by some historians to have belonged to a senior officer. [Goldsworthy (2003) 202] Other academics, in contrast, consider that silver-sheathed helmets may have been widely worn by "comitatus" soldiers, given as a form of pay or reward. [ Bishop and Coulston, (2006) 214-215.]


The legionary "scutum", a convex rectangular shield also disappeared during the 3rd century. All troops adopted the auxiliary oval (or sometimes round) shield ("clipeus"). [Elton (1996) ] Shields, from examples found at Dura and Nydam, were of vertical plank construction, the planks glued, and faced inside and out with painted leather. The edges of the shield were bound with stitched rawhide, which shrank as it dried improving structural cohesion. It was also lighter than the edging of copper alloy used in earlier Roman shields. [Bishop and Coulston (2006) 217]

Hand weapons

The "gladius", a short (median length: 460 mm) stabbing-sword that was designed for close-quarters fighting, and was standard for the Principate infantry (both legionary and auxiliary), also was phased out during the 3rd century. The infantry adopted the "spatha", a longer (median length: 760mm) sword that during the earlier centuries was used by the cavalry only. [Goldsworthy (2003) 205] However, alongside the "spatha" Vegetius mentions the use of shorter-bladed swords termed "semispathae." [Bishop and Couslton (2006) 202] At the same time, infantry acquired a heavy thrusting-spear ("hasta") which became the main close order combat weapon to replace the "gladius", as the "spatha" was too long to be swung comfortably in tight formation (although it could be used to stab). These trends imply a greater emphasis on fighting the enemy "at arm's length". [Elton (1996) 110] In the 4th century, there is no archaeological or artistic evidence of the "pugio" (Roman military dagger), which is attested until the 3rd century. 4th century graves have yielded short, single-edged knives in conjunction with military belt fittings. [Bishop and Coulston (2006) 205]


In addition to his thrusting-spear, a late foot soldier might also carry a throwing-spear ("verrutum") or a "spiculum", a kind of heavy, long "pilum", similar to an angon. Alternatively, a couple of short javelins ("lanceae"). Late infantrymen often carried half a dozen lead-weighted throwing-darts called "plumbatae" (from "plumbum" = "lead"), with an effective range of ca. 30 m, well beyond that of a javelin. The darts were carried clipped to the back of the shield. [Goldsworthy (2000) 167; (2003) 205] The late foot soldier thus had greater missile capability than his Principate predecessor, who was usually limited to just one "pilum". [Goldsworthy (2000) 168] Late archers continued to use the recurved composite bow as their standard. This was a sophisticated, compact and powerful weapon, suitable for mounted and foot archers alike (the cavalry version being more compact than the infantry's). A small number of archers may have been armed with crossbows ("manuballistae"). [Elton (1996) 108]

Supply infrastructure

A critical advantage enjoyed by the late army over all its foreign enemies except the Persians was a highly sophisticated organisation to ensure that the army was properly equipped and supplied on campaign.In the 4th century, the production of weapons and equipment was highly centralised (and presumably standardised) in a number of major state-run arms factories ("fabricae") documented in the "Notitia". It is unknown when these were first established, but they certainly existed by the time of Diocletian. [Jones (1964) ] In the 2nd century, there is evidence of "fabricae" inside legionary bases and even in the much smaller auxiliary forts, staffed by the soldiers themselves. [Goldsworthy (2003) 88, 149] But there is no evidence, literary or archaeological, of "fabricae" outside military bases and staffed by civilians during the Principate (although their existence cannot be excluded, as no archaeological evidence has been found for the late "fabricae" either). Late "fabricae" were located in border provinces and dioceses. [Elton (1996) 116] Some were general manufacturers producing both armour and weapons ("fabrica scutaria et armorum") or just one of the two. Others were specialised in one or more of the following: "fabrica spatharia" (sword manufacture), "lanciaria" (spears), "arcuaria" (bows), "sagittaria" (arrows), "loricaria" (body armour), "clibanaria" (cataphract armour), and "ballistaria" (catapults). ["Notitia" Titles Oriens XI, Occidens IX]

Like their enemies, the late army could rely on foraging for supplies when campaigning on enemy soil. But this was obviously undesirable on Roman territory and impractical in winter. The empire's complex supply organisation enabled the army to campaign in all seasons and in areas where the enemy employed a "scorched earth" policy. The responsibility for supplying the army rested with the "praefectus praetorio" of the operational sector. He in turn controlled a hierarchy of civilian authorities (diocesan "vicarii" and provincial governors), whose agents collected, stored and delivered supplies to the troops direct or to predetermined fortified points. [Elton (1996) 236] The quantities involved were enormous and would require lengthy and elaborate advance planning for major campaigns. A late legion of 1,000 men would require a minimum of 2.3 tonnes of grain-equivalent "every day". [Elton (1996) 237] An imperial escort army of 25,000 men would thus require around two million tonnes of grain-equivalent for a month's campaign (plus fodder for the horses).

Such vast cargoes would be carried by boat as far as possible, by sea and/or river, and only the shortest possible distance overland. That is because transport on water was far more economical than on land (as it remains today, although the differential is smaller). Land transport of military supplies on the "cursus publicus" (imperial transport service) was typically by wagons ("angariae"), with a maximum legal load of 1,500 lbs (680 kg), drawn by two pairs of oxen. [Jones (1964) 831] A standard Roman freighter-ship of the period had a capacity of ca. 100 tonnes. [Jones (1964) 843] Thus, such a vessel, with a 30-man crew, could carry the same load as ca. 150 wagons (which required 150 drivers and 600 oxen, plus pay for the former and food for all). It could also, with a favourable wind, travel much faster than the typical 3 km/h achieved by the wagons. [Jones (1964) 842] According to the available shipping-rates, it was cheaper to transport a cargo by sea from Syria to Lusitania (i.e. the entire length of the Mediterranean, ca. 5,000 km) than just 110 km overland. [Jones (1964) 841] Against this must be set the fact that freighters, which carried square sails only, could only progress if there was favourable wind. Maritime transport was completely suspended for at least four months in the winter (as stormy weather made it too hazardous) and even during the rest of the year, shipwrecks were common. [Jones (1964) ]

It is thus likely that the establishment of the empire's frontier on the Rhine-Danube line was dictated by the logistical need for large rivers to accomodate supply ships more than by defensibility. These rivers were dotted with dedicated military supply docks ("portus exceptionales"). [Jones (1964) 844] The protection of supply convoys on the rivers was the responsibility of the fluvial flotillas ("classes") under the command of the riverine "duces". The "Notitia" gives no information about the Rhine flotillas (as the Rhine frontier had collapsed by the time the Western section was compiled), but mentions four "classes Histricae" (Danube flotillas) and eight other "classes" in tributaries of the Danube. Each flotilla was commanded by a "praefectus classis" who reported to the local "dux". It appears that each "dux" on the Danube disposed of at least one flotilla (one, the "dux Pannoniae", had three). ["Notitia" "Oriens" Titles XXXIX to XLII and "Occidens" Titles XXXII to XXXIV]


Compared to the 1st and 2nd centuries, the 3rd and 4th centuries saw much greater fortification activity, with many new forts built. [Goldsworthy (2003) 206] Later Roman fortifications, both new and upgraded old ones, contained much stronger defensive features than their earlier counterparts. In addition, the late 3rd/4th centuries saw the fortification of many towns and cities including the City of Rome itself and its eastern sister, Constantinople. [Elton (1996) 161–71]

According to Luttwak, Roman forts of the 1st/2nd centuries, whether "castra legionaria" (inaccurately translated as legionary "fortresses") or auxiliary forts, were clearly residential bases that were not designed to withstand assault. The typical rectangular "playing-card" shape, the long, thin and low walls and shallow ditch and the unfortified gates were not defensible features and their purpose was delimitation and keeping out individual intruders. [Luttwak (1976) 134–5] This view is too extreme, as all the evidence suggests that such forts afforded a significant level of protection, even the more rudimentary early type based on the design of marching-camps (ditch, earth rampart and wooden palisade). The latter is exemplified by the siege of the legionary camp at "Castra Vetera" (Xanten) during the revolt of the Batavi in 69-70 AD. 5,000 legionaries succeeded in holding out for several months against vastly superior numbers of rebel Batavi and their allies under the renegade auxiliary officer Civilis, despite the latter disposing of ca. 8,000 Roman-trained and equipped auxiliary troops and deploying Roman-style siege engines. (The Romans were eventually forced to surrender the fort by starvation). [Tacitus "Historiae" IV.22, 23, 29, 30, 60]

Nevertheless, later forts were built to much higher defensive specifications than their 2nd century predecessors, including the following features:
# Deeper (average: 3 m) and much wider (av. 10 m) perimeter ditches ("fossae"). These would have flat floors rather than the traditional V-shape. [Goldsworthy (2003) 206] Such ditches would make it difficult to bring siege equipment (ladders, rams, and other engines) to the walls. It would also concentrate attackers in an enclosed area where they would be exposed to missile fire from the walls. [Elton (1996) 161]
# Higher (av. 9 m) and thicker (av. 3 m) walls. Walls were made of stone or stone facing with rubble core. The greater thickness would protect the wall from enemy mining. The height of the walls would force attackers to use scaling-ladders. The parapet of the rampart would have crenellations to provide protection from missiles for defenders. [Elton (1996) 163]
# Higher (av. 17.5 m) and projecting corner and interval towers. These would enable enfilading fire on attackers. Towers were normally round or half-round, and only rarely square as the latter were less defensible. Towers would be normally be spaced at 30 m intervals on circuit walls. [Elton (1996) 162–3]
# Gate towers, one on each side of the gate and projecting out from the gate to allow defenders to shoot into the area in front of the entrance. The gates themselves were normally wooden with metal covering plates to prevent destruction by fire. Some gates had portcullises. Postern gates were built into towers or near them to allow sorties. [Elton (1996) 164]

More numerous than new-build forts were old forts upgraded to higher defensive specifications. Thus the two parallel ditches common around earlier forts could be joined by excavating the ground between them. Projecting towers were added. Gates were either rebuilt with projecting towers or sealed off by constructing a large rectangular bastion. The walls were strengthened by doubling the old thickness. Upgraded forts were generally much larger than new-build. New forts were rarely over one hectare in size and were normally placed to fill gaps between old forts and towns. [Elton (1996) 165–7] However, not all of the old forts that continued to be used in the 4th century were upgraded e.g. the forts on Hadrian's Wall and some other forts in Britannia were not significantly modified. [Elton (1996) 167]

The main features of late Roman fortification clearly presage those of medieval castles. But the defensibility of late Roman forts must not be exaggerated. Late Roman forts were not always located on defensible sites, such as hilltops and they were not designed as independent logistic facilities where the garrison could survive on internal supplies (water in cisterns or from wells and stored food) for months or even years. They remained bases for troops that would sally out and engage the enemy in the field. [Isaac (1992) 198]

Nevertheless, the benefits of more defensible forts are evident: they could act as temporary refuges for overwhelmed local troops during barbarian incursions, while they waited for reinforcements. The forts were difficult for the barbarians to take by assault, as they generally lacked the necessary equipment. The forts could store sufficient supplies to enable the defenders to hold out for a few weeks, and to supply relieving troops. They could also act as bases from which defenders could make sorties against isolated groups of barbarians and to cooperate with relieving forces. [Luttwak (1976) 132–4]

The question arises as to why the 4th century army needed forts with enhanced defensive features whereas the 2nd century army apparently did not. Luttwak argues that defensible forts were an integral feature of a 4th century defence-in-depth "grand strategy", while in the 2nd century "preclusive defence" rendered such forts unnecessary . But the existence of such a "strategy" is strongly disputed by several scholars, as many elements of the late Roman army's posture were consistent with continued forward defence. [Mann (1979) 175–83] An alternative explanation is that preclusive defence was still in effect but was not working as well as previously and barbarian raids were penetrating the empire more frequently.(see Strategy, below)

Strategy and tactics


Edward Luttwak's "Grand Strategy of the Roman Empire" (1976) launched the thesis that in the 3rd and early 4th centuries, the empire's defence strategy mutated from "forward defence" (or "preclusive defence") in the Principate to "defence-in-depth" in the 4th century. According to Luttwak, the Principate army had relied on neutralising imminent barbarian incursions before they reached the imperial borders. This was achieved by stationing units (both legions and auxiliary regiments) right on the border and establishing and garrisoning strategic salients beyond the borders. The response to any threat would thus be a pincer movement into barbarian territory: large infantry and cavalry forces from the border bases would immediately cross the border to intercept the coalescing enemy army. [Luttwak (1976) Fig.3.3]

According to Luttwak, the forward defence system was always vulnerable to unusually large barbarian concentrations of forces, as the Roman army was too thinly spread along the enormous borders to deal with such threats. In addition, the lack of any reserves to the rear of the border entailed that a barbarian force that successfully penetrated the perimeter defences would have unchallenged ability to rampage deep into the empire before Roman reinforcements from other border garrisons could arrive to intercept them. [Luttwak (1976) 136]

The essential feature of defence-in-depth, according to Luttwak, was an acceptance that the Roman frontier provinces themselves would become the main combat zone in operations against barbarian threats, rather than the barbarian lands across the border. Under this strategy, border forces would not attempt to repel a large incursion. Instead, they would retreat into fortified strongholds and wait for mobile forces ("comitatenses") to arrive and intercept the invaders. Border forces would be substantially weaker than under forward defence, but their reduction in numbers (and quality) would be compensated by the establishment of much stronger fortifications to protect themselves. [Luttwak (1976) 132]

But the validity of Luttwak's thesis has been strongly disputed by a number of scholars, especially in a powerful critique by B. Isaac, the author of a leading study of the Roman army in the East (1992). [J. C. Mann in "Journal of Roman Studies" 69 (1979)] [F. Miller in "Britannia" 13 (1982)] [Isaac (1992) 372–418] Isaac claims that the empire did not have the intelligence capacity or centralised military planning to sustain a grand strategy e.g. there was no equivalent to a modern army's general staff. [Isaac (1992) 378, 383, 401–6] In any case, claims Isaac, the empire was not interested in "defence" at all: it was fundamentally aggressive both in ideology and military posture, up to and including the 4th century. [Isaac (1992) 387–93]

Furthermore, there is a lack of substantial archaeological or literary evidence to support the defence-in-depth theory. [Mann (1979) 180–1] (a) J.C. Mann points out that there is no evidence, either in the "Notitia Dignitatum" or in the archaeological record, that units along the Rhine or Danube were stationed in the border hinterlands. [Mann (1979) 180] On the contrary, virtually all forts identified as built or occupied in the 4th century on the Danube lay on, very near or even beyond the river, strikingly similar to the 2nd century distribution. [C. Scarre "Penguin Historical Atlas of Ancient Rome" (1995) 87 (map)] [Elton (1996) 157, 159 (Fig 13)]

Another supposed element of "defence-in-depth" were the "comitatus praesentales" (imperial escort armies) stationed in the interior of the empire. But Luttwak himself admits that these were too distant from the frontier to be of much value in intercepting barbarian incursions. [Luttwak (1976) 190] Their arrival in theatre could take weeks, if not months. [Elton (1996) 215] Although they are often described as "mobile field armies", in this context "immobile" would be a more accurate description. A traditional view is that the escort armies' role was precisely as a strategic reserve of last resort that could intercept really large barbarian invasions that succeeded in penetrating deep into the empire (such as the invasions of the late 3rd century). But this theory conflicts with the fact the large "comitatus" was not established before 312, by which time there had not been a successful barbarian invasion for ca. 40 years. Hence the mainstream modern view that the "praesentales" armies central role was as insurance against usurpers. [Goldsworthy (2000) 170]

Luttwak terminates his analysis at the end of Constantine's reign, before the establishment of the regional "comitatus". Unlike the imperial escort armies, these were close enough to the theatre of operations to succour the border troops. But their stationing may have differed little from the location of legions in the 2nd century, even though they apparently wintered inside cities, rather than in purpose-built legionary bases. [Mann (1979) 181] For example, the two "comitatus" of Illyricum (East and West) are documented as wintering in Sirmium, which was the site of a major legionary base in the Principate. [Elton (1996) 209]

Furthermore, the late empire maintained a central feature of Principate forward defence: a system of treaties of mutual assistance with tribes living on the imperial frontiers. The Romans would promise to defend the ally from attack by its neighbours. In return, the ally would promise to refrain from raiding imperial territory, and prevent neighbouring tribes from doing the same. Although the allies would officially be denoted "tributarii" (i.e. subject to paying tribute to Rome, in cash or in kind), in practice the loyalty of the ally was often secured by gifts or regular subsidies from Rome. This practice was applied on all the frontiers. [Jones (1964) 611] The Romans continued to assist the client tribes to defend themselves in the 4th century. For example, Constantine I's army constructed two massive lines of defensive earthworks, 100–250 km beyond the Danube, totalling ca. 1,500 km in length, the Devil's Dykes in Hungary/Romania and the Brazda lui Novac de Nord in Romania. Garrisoned by a mix of Roman and native troops, their purpose was to protect Dacian and Sarmatian tributary tribes of the Tisza and Wallachian plains against Gothic incursions. This created a Transdanubian buffer zone, extending from "Aquincum" (Budapest) all the way to the Danube delta, obviously contradicting the proposition that the empire's Danubian border provinces were themselves envisaged as buffer zones. [Scarre "Atlas" 87] (This was especially unlikely in the case of these regions, as the Illyrian emperors and officer class that dominated the late army would hardly relish seeing their native provinces reduced to combat zones).

Late Roman emperors continued major and frequent offensive operations beyond the imperial borders throughout the 4th century. These were strikingly similar to the pincer movements described by Luttwak as being characteristic of forward defence in the early Principate. For example, Valentinian I's campaign against the Quadi in 375. [Ammianus XVI.11] Julian in 356–60 and Valentinian I in 364–9 carried out annual operations across the Rhine designed to force the submission of local tribes and their acceptance of "tributarii" status. [Ammianus books ]

The late army's "defence" posture thus contains many elements that are similar to the Principate army's, raising the question of whether defence-in-depth was ever in reality contemplated (or implemented) as a strategy. But the debate about defence-in-depth is still very much alive in academic circles.

Role of cavalry

A traditional thesis is that cavalry assumed a much greater importance in the 4th century army than it enjoyed in the 2nd century. According to this view, cavalry increased significantly as a proportion of the total forces and took over the leading tactical role from the infantry. It also enjoyed much higher status than in the 2nd century. At the same time, the infantry declined in efficiency and value in operations, leaving the cavalry as the effective arm. In fact, there is no good evidence to support this view, and plenty of evidence against it. [Goldsworthy (2000) 169]

As regards numbers, the mid-2nd century army contained ca. 80,000 cavalry out of ca. 385,000 total effectives i.e. cavalry constituted ca. 21% of the total forces. [Holder (2003) 120] For the late army, about one third of the army units in the "Notitia" are cavalry, but in numbers cavalry were a smaller proportion of the total because cavalry units were on average smaller than infantry units. [Elton (1996) 106] For example, in the "comitatus", cavalry "vexillationes" were probably half the size of infantry "legiones". Overall, the available evidence suggests that the proportion of cavalry was much the same as in the 2nd century. Examples: in 478, a "comitatus" of 38,000 men contained 8,000 cavalry (21%). [Elton (1996) 105–6] In 357, the "comitatus" of Gaul, 13-15,000 strong, contained an estimated 3,000 cavalry (20-23%). [Elton (1996) ]

As a consequence, most battles in the 4th century were, as in previous centuries, primarily infantry encounters, with cavalry playing a supporting role. The main qualification is that on the Eastern frontier, cavalry played a more prominent role, due to the Persian reliance on cavalry as their main arm. This obliged the Romans to strengthen their own cavalry element, in particular by increasing the number of "cataphracti". [Goldsworthy (2003) 205]

The supposedly higher status of cavalry in the 4th century is also open to doubt. This view is largely based on underestimating the importance of cavalry in the 2nd century. [Goldsworthy (2000) 169] Cavalry always had higher status than infantry in the Principate: in the time of Domitian (r. 81–96), auxiliary cavalry was paid 20-40% more than auxiliary infantry. [Hassall (2000) 336]

The view of some modern scholars that the 4th century cavalry was a more efficient service than the infantry was certainly not shared by Ammianus and his contemporaries. Ammianus describes three major battles which were actually or nearly lost due to the incompetence or cowardice of the Roman cavalry. [Tomlin (1998) 117–8] (1) The Battle of Strasbourg (357), where the cavalry, including cataphracts, were routed by their German counterparts at an early stage, leaving the Roman infantry right wing dangerously exposed. After fleeing behind the infantry lines, it took the personal intervention of Julian to rally them and persuade them to return to the fight. (The cataphracts were later ordered to wear female clothes by Julian as punishment). [Ammianus XVI.12] (2) During his Persian campaign (363), Julian was obliged to sanction two cavalry units for fleeing when caught by surprise attacks (one unit was decimated, the other dismounted). Later, the "Tertiaci" cavalry regiment was ordered to march with the camp followers for deserting the field just as the infantry was on the point of breaking the Persian line. (3) At the Battle of Adrianople (378), the Roman cavalry was largely responsible for the catastrophic defeat. "Scholae" units started the battle by an unauthorised attack on the enemy wagon circle, at a moment when their emperor Valens was still trying to negotiate a truce with the Goths. The attack failed, and when the Gothic cavalry appeared, the Roman cavalry fled, leaving the Roman infantry left wing exposed. The Gothic cavalry then routed the Roman left wing, and the battle was as good as lost. [Ammianus XXXI]

In contrast, the excellent performance of the infantry, both "comitatenses" and "limitanei", is a recurrent feature of Ammianus' history. At the Persian siege of Amida, Ammianus' eye-witness account describes the city's defence by "limitanei" units as skilful and tenacious, if ultimately unsuccessful. [Ammianus XIX.1–8] At Strasbourg (357), the infantry showed remarkable skill, discipline and resilience throughout, saving the day at two critical moments.(see Battle of Strasbourg for a detailed account). [Goldsworthy (2000) 176–7] Even at the disaster of Adrianople, the Roman infantry fought on, despite being abandoned by their cavalry and surrounded on three sides by overwhelmingly superior numbers of Goths. [Ammianus XXXI.13]


Just as the armour and weapons of the late army were fundamentally similar to those of earlier eras, so the army's tactics were based on traditional principles. The key elements of systematic scouting, marching formation, battle array, fortified camping, and siegecraft were all followed intact in the late period. [Elton (1996) 243-63] This section examines aspects of late tactics that differed significantly from Principate tactics.

One striking difference was that late army doctrine (and practice) aimed at avoiding open battle with the enemy if possible, unlike the early Principate doctrine of seeking to bring the enemy to battle as often and as quickly as possible. [Goldsworthy (2000) 182] [Elton (1996) 216] The main motivation was likely not a reduced ability to win such encounters. The late army continued to win the great majority of its battles with barbarians. [Elton (1996) 218] Rather, the primary concern seemed to be the need to minimise casualties. [Goldsworthy (2000) 182] Pitched battles generally resulted in heavy losses of high-grade "comitatenses" troops, which could not be easily replaced. This in turn supports the hypothesis that the late army had greater difficulty than the Principate in finding sufficient recruits, and especially high-quality recruits. The late army preferred to attack the enemy by stealth or stratagem: ambushes, surprise attacks, harassment and manoeuvres to corner the enemy in zones where they could not access supplies and from which they could not escape (e.g. by blocking mountain passes or river crossings). [Elton (1996) 216, 218-9]

Where battle could not be avoided, the late army broadly followed traditional practice as regards array. Heavy infantry would be drawn up in a main line, normally straight and several ranks deep. Mounted archers were stationed, together with light-armed slingers, in front of the main infantry line. Cavalry would be posted on the wings (light cavalry on the outside). Foot archers would form the rear rank(s) of the main infantry line. [Arrian "Acies contra Alanos"] There would be a reserve infantry and cavalry line of variable size to the rear of the main line, in order to deal with breaches in the main line and to exploit opportunities. At a distance of a mile or so to the rear of the army, its fortified camp of the previous night would contain its assistants and baggage, guarded by a small garrison. The camp could act as a refuge if the army was put to flight. Roman armies in the field never camped overnight without constructing defences. A ditch would be dug around the perimeter of the camp, and the spoil used to erect a rampart, which would then be topped with a palisade of sharpened wooden stakes arranged cross-hatched to form an impenetrable screen. Such defences, systematically patrolled, effectively precluded surprise attacks and enabled the troops to get a good night's sleep. [Elton (1996) 251-2]

Where the late army appears to have evolved to some extent is in battle tactics. The early Principate army had relied on a barrage of heavy javelins ("pila") followed by a shock infantry charge, which was often sufficient to shatter, or at least disorganise, the barbarian line. After that, legionaries were trained to engage in aggressive "mano-a-mano" combat, striking the enemy in the face with the boss of their heavy shields ("scuta") and stabbing them viciously with short swords ("gladii"). Such tactics very often resulted in the rout of the less well-equipped and trained barbarian foe. [Goldsworthy (2000) 169] The mounted archers and slingers in front of the main infantry line would loose their missiles on the enemy before the infantry lines engaged and would then hastily retreat to the rear of their own infantry line, whence, in conjunction with the foot archers already there, they would loose a continuous rain of missiles on the enemy foot by shooting over the heads of their own infantry. [Goldsworthy (2000) 137] The cavalry's task on each wing was to scatter the enemy cavalry facing them and then, if possible, to encircle the main body of enemy infantry and attack them from the flanks and rear.

In the late army, while the role of archers and cavalry remained similar, the infantry relied less on the charge and more on steady pressure in close formation. The thrusting-spear (2-2.5m long) had replaced the "gladius" (just 0.5m long) as the primary mêlée weapon. [Elton (1996) 109] The extended reach of the thrusting-spear, combined with the adoption of oval or round shields, permitted a battle array where shields were interlocked to form a "shield wall". [Ammianus XVI.12 (para. 44)] [Lendon (2005) 261-268] Spears would protrude through the 'V' shaped gaps formed between overlapping shields. The late army also relied more heavily on missiles.

This kind of combat was consistent with the aim of minimising casualties and its efficacy is illustrated by the Battle of Strasbourg. The battle was primarily a struggle of attrition where steady pressure on the barbarians resulted in their eventual rout. Despite a long and hard-fought struggle, Roman casualties were negligible. [Goldsworthy (2000) ]

The "barbarisation" theory

thumb|right|200px|Drawing_of_Flavius Stilicho, the barbarian-born general who was "magister peditum" (commander-in-chief) of West Roman forces 395–408. The general is depicted in the standard attire of a common foot soldier of the time when not in combat, wearing a "chlamys" (military cloak) over his tunic and carrying a heavy thrusting-spear and oval shield (in combat most late soldiers wore mail shirts and helmets). He was made a scapegoat for the barbarian invasions of 405–6, although in reality his military skill may have saved the West from early collapse. Derived (1848) from an ivory diptych at Monza, Italy] The barbarisation theory, ultimately derived from Edward Gibbon's 18th-century "magnum opus", "The Decline and Fall of the Roman Empire", contains two propositions. (1) That the late army recruited much greater numbers of barbarian-born troops than the Principate army; and (2) that the greater number of barbarian recruits resulted in a major decline of the army's effectiveness and was a major factor in the collapse of the Western Roman empire. As discussed above, proposition (1) is probably correct, although it should be borne in mind that probably ca. 75% of the late army's recruits remained Roman-born. This section discusses proposition (2).

According to this view, the barbarian officers and men recruited by the late army, coming from tribes that were traditional enemies of Rome, had no real loyalty to Rome and often betrayed her interests, colluding with invading barbarian tribes, especially if those tribes were their own. At the same time, the spread of barbarian customs and culture led to a decline in traditional military discipline, and internal army disunity due to friction between Romans and barbarians. Ultimately, the army degenerated into just a collection of foreign mercenary bands that were incapable of defending the empire effectively. [Goldsworthy (2003) 208]

According to the historian A.D. Lee, there is little evidence to support this view and compelling reasons to reject it. Firstly, the late army clearly was not, and did not become, ineffective. The regular army in the West remained a formidable force until the political disintegration of the West in the period after 406. It continued to win most of its major encounters with barbarian forces e.g. the defeat of Radagaisus in 405. [Lee (1997) 233] Even after 406, the "comitatus" of the West rarely suffered defeats at the hands of barbarians, but progressively shrank in numbers to almost nothing over the period 395-476 as the Western government could no longer raise the necessary recruits and funds to replace losses incurred in civil wars and campaigns against barbarians. For example, it appears the Western "comitatus" contained 25% fewer first-grade regiments in 420 compared to 395. [Heather (2005) 248] In any case, the Eastern empire did not collapse, even though its army contained at least the same proportion of barbarians as the West, if not greater. An analysis of the ethnicity of Roman army officers named in the sources shows that in the period 350–99, 23% were probably barbarian-born. The same figure for period 449–76 officers, virtually all Easterners (as the Western army had largely dissolved) was 31%. [Elton (1996) 148] In the "Notitia", 55 Eastern regiments carry barbarian names, compared with 25 in the Western army. ["Notitia Dignitatum" passim]

Recorded incidents of alleged barbarian treachery in the regular army are very few and isolated. There is a tendency by some modern scholars to ascribe to ancient barbarians a degree of ethnic solidarity that did not exist, according to A.H.M. Jones. For example, Germanic tribes were constantly fighting each other and even within such tribal confederations as the Franks or Alamanni there were bitter feuds between the constituent tribes and clans. The few known conflicts of loyalty only arose when the Roman army was campaigning against a barbarian-born soldier's own specific clan. [Jones (1964) 622] Ammianus himself never characterises barbarian-born troops as unreliable. [Jones (1964) 621–2] On the contrary, his evidence is that barbarian soldiers were as loyal, and fought as hard, as Roman ones. [Elton (1996) 138]

Most damningly for the theory, barbarian-born troops appear to have been especially concentrated in the elite units of the imperial escort armies. In the crack "auxilia palatina" infantry regiments, the proportion of barbarians in the ranks appears to have numbered anywhere between a third and a half of effectives. [Elton (1996) 151] This implies that they were considered highly reliable, as well as of first-rate combat capability. [Lee (1997) 224]

In conclusion, the barbarisation theory is rejected by many scholars as regards the regular Roman army of the 4th century. On the contrary, it is likely that barbarian recruitment was crucial to the army's continued existence, by providing a badly-needed source of first-rate recruits. [Jones (1964) 621] [Elton (1996) 152] [Lee (1997) 223–4] [Goldsworthy (2003) 209]




* Ammianus Marcellinus, " [ Roman History] " (late 4th c.)
* Zosimus, " [ Historia Nova] " (5th century)
* "Notitia Dignitatum", " [ Augustana] " (late 4th/early 5th c.)


*cite book |last=Barlow and Brennan |first=J. & P. |title=Tribuni Scholarum Palatinarum c. A.D. 353-64: Ammianus Marcellinus and the Notitia Dignitatum in The Classical Quarterly, New Series, Vol. 51, No. 1, pp. 237-254 |year=2001
* cite book |last=Woods |first=David |title="Subarmachius, Bacurius, and the Schola Scutariorum Sagittariorum" in Classical Philology, Vol. 91, No. 4 (Oct.), pp. 365-371, The University of Chicago Press

See also

* Roman auxiliaries
* East Roman army
* Structural history of the Roman military
* Battle of Strasbourg

External links

* [ Late Roman army reenactors]
* [ Comitatus] Historical reenactment and Living history group portraying the Late Roman army in northern England.

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