Battle of Nesjar

The Battle of Nesjar was a sea battle off the coast of Norway in 1015 or 1016, in Oslofjord. The exact location is unknown, but it is somewhere in today's Langesundfjorden. The fighting parties were the throne claimant Olav Haraldsson (later Saint Olav) on one side, and an alliance backing the Swedish vassal Sveinn Hákonarson on the other.

After the defeat of Olav Tryggvason at the Battle of Svolder, Norway had been divided into a Swedish part governed by Sveinn and a Danish part run by Eiríkr Hákonarson. However, after Eiríkr joined his brother-in-law Canute the Great in his campaign to conquer England, Danish rule folded, and power was assumed by Olav Haraldsson, a throne claimant from the Harald Fairhair family line.

Sveinn, who was based in Trøndelag, learned that Olav was rallying support in Eastern Norway. He set sail along the coast of Norway. Along the way he joined forces with those of several allies among Norway's farmer-chieftains. The most prominent of these was Erling Skjalgsson.

Olav, on the other hand, had finished raising his forces, and had begun his trip northwards to confront Sveinn. The fleets clashed off the coast of today's Telemark. Few accounts of the battle survive; however, it is generally regarded as a fierce battle with heavy casualties. None of the major players were killed, as would be usual in this age of chieftains leading the line. However, Sveinn was chased off and fled to Sweden, thus relinquishing his grip on power.

The road now seemed open for Olav to establish a unified rule of Norway. However, along the way he was later forced to ally with Erling Skjalgsson, an alliance which was always uneasy. It also ended violently when Erling was killed in connection with the battle of Boknafjorden in 1028. His followers got revenge two years later, when Olav Haraldsson himself was killed in the battle of Stiklestad.

Sigvatr Þórðarson composed the poem "Nesjavísur" on the battle.