2500 men lost their lives.
It was a naval battle that was fought between King Sverre Sigurdsson, leader of the Birkebeiner party, and Sigurd Magnusson, the Øyskjegg party pretender.
Although there had been previous revolts during Sverre's reign following his usurpation of the throne in 1184, the revolt in support of Sigurd Magnusson (son of former king Magnus Erlingsson) became far more threatening than the attempts of previous pretenders.
As Sigurd was a minor, the actual leaders behind the revolt were Hallkjell Jonsson and Olav Jarlsmåg. The Øyskjeggs recruited their initial army in Orkney and Shetland. The army sailed to the south-eastern part of Norway in 1193 with 23 ships and 2,000 men, and had Sigurd proclaimed king at the Haugating.
This force was commonly called the Øyskjeggs, meaning the "island-men", although they themselves preferred to be called the Gullbeiner ("gold-legs"), as opposed to their opponents, the Birkebeiner ("birch-legs").
The Øyskjeggs sailed for a brief raid for booty in Denmark, and after returning to Norway, they took control over the Western, Southern, and Eastern part of the country. Sigurd and the Øyskjeggs took base in Bergen for the winter, although they failed to take the castle Sverresborg which was defended by 300 loyal Birkebeiners.
After hearing news of the Øyskjegg offence, Sverre gathered his troops and sailed south from his base in Nidaros (Trondheim) with 20 ships. When Sverre was closing in on Bergen on 2 April, the Øyskjeggs went to their ships and sailed across Byfjorden to the bay of Florvåg, off the southeastern side of the island Askøy.
After gaining intelligence of Øyskjegg plans of a counter-attack, Sverre set out to surprise the Øyskjeggs with an attack before dawn. The Birkebeiner fleet approached the bay of Florvåg early 3rd of April, Palm Sunday, while it was still dark.
The Øyskjeggs did not know of the attack until they heard the noise from the Birkebeiner ships crushing into their own ships. breaking many of the oars.
As the Birkebeiner warriors guarded themselves with their shields, the Øyskjeggs found no targets to shoot at until the Birkebeiner finally charged at the Øyskjeggs.
The Øyskjeggs had an advantage since their ships were taller than those of the Birkebeiner, and they managed to pull Sverre's own royal ship towards them, killing all the archers and capturing the royal banner Sigerflua.
After heavy losses on both sides, the Birkebeiner managed to shake off the Øyskjegg fleet and started a retreat. The Øyskjeggs began chasing the Birkebeiner, but since their oars had been broken, the Øyskjegg ships were suddenly dragged into a strong current, and the Birkebeiner fleet returned to attack the ships of the Øyskjeggs.
The Birkebeiner also gained reinforcements of a fresh ship with 100 men from Sverresborg, and easily defeated the Øyskjeggs, one ship at a time.
Only two Øyskjegg ships managed to get away, and except for some men who requested pardoning, the majority of the Øyskjegg forces were killed, including Sigurd Magnusson, Hallkjell Jonsson and Olav Jarlsmåg.