Entasis

In architecture, entasis is the application of a convex curve to a surface for aesthetic purposes. Its best-known use is in certain orders of Classical columns that bulge slightly in the middle.

Examples

Probably the first use of entasis was in the construction of the Egyptian pyramids, but it can also be observed in Classical period Greek column designs, for example in the Doric-order temples in Segesta, Selinus, Agrigento and Paestum. It was only very rarely used in Hellenistic and Roman period architecture. The temples built during these periods were higher than those of the Greeks, with longer and thinner columns. Noted architects such as the Renaissance master Andrea Palladio also used it in their buildings.

More recently, Rolls-Royce cars all made use of it in their radiator grills to give an illusion of greater solidity.

Purpose

The early Classical builders did not leave an explanation of their reasons for using entasis, and there are several differing opinions as to its purpose. Some descriptions of entasis ["entasis", article by Anthony Rich, Jun. B.A. of Caius College, Cambridge, on p461 of William Smith, D.C.L., LL.D.:"A Dictionary of Greek and Roman Antiquities", John Murray, London, 1875. [http://penelope.uchicago.edu/Thayer/E/Roman/Texts/secondary/SMIGRA*/Entasis.html] ] state simply that the technique was an enhancement applied to the more primitive conical columns to make them appear more substantial. Trevelyan believed that the effect represented strength by imitating the swelling of a strained muscle. [George Trevelyan, "The Active Eye in Architecture", The Wrekin Trust, 1977 [http://www.sirgeorgetrevelyan.org.uk/books/thtbk-arch03.html (online version)] ] This accords well with the etymology of the word, from the Greek meaning 'to strain'. ["entasis", Oxford English Dictionary, Second Edition 1989]

Another popular view is that entasis was intended to correct an optical illusion that makes cylindrical columns appear pinched and flat surfaces appear convex. This explanation was given by Hero of Alexandria, for example. [
Hero of Alexandria, "Horoi ton geometrias onomaton", 135, 14: "Thus, since a cylindrical column would, when looked at, seem irregularly narrower in the middle, he makes this part of it wider" (translation given by Ralph Hancock, The Department of Greek and Latin at The Ohio State University) [http://omega.cohums.ohio-state.edu/mailing_lists/CLA-L/2000/11/0299.php] ] However, it does not explain the case of one well-known example, Paestum, where the entasis is so pronounced that it creates an obvious curvature, not an illusion of straightness. Conversely, in the Parthenon, the entasis is so subtle that it has almost no effect on the apparent shape of the columns, so is insufficient to correct any supposed illusion of curvature.

An earlier and also lesser-known architectural practice was the application of a concave curve to the interior surface, symmetric to Entasis, and known as 'Ekstasis'. Dating to at least Mycenean time but perhaps before, an 'ekstatic' curve was believed to have a virtually magnetic power, quickly drawing those nearby into close proximity. Travellers have reported being subjected to Ekstatic effects in Hephaestus' temple in Aegina, in ancient Mystra north of Sparta, in the old temples atop Monemvasia, in the holy site now known as the church of St. Stephen near the tomb of Ptolemy II on Santorini (Thira) and in what is now known as Agamemnon's Tomb close by the ancient city of Mycenae.

It has also been argued that a 'stunted cycloid' column that bulges in the middle is stronger than a column with straight sides. [Peter Thompson et al., "Entasis: architectural illusion compensation, aesthetic preference or engineering necessity?", Journal of Vision, Volume 7, Number 9, ISSN 1534-7362 [http://www.journalofvision.org/7/9/355/(abstract)] - abstract argues against traditional explanations for entasis and mentions possible engineering reason]

Literature

* Thomä, Walter: "Die Schwellung der Säule (Entasis) bei den Architekturtheoretikern bis in das XVIII. Jahrhundert." Dresden 1915.

References