Dictionary of National Biography, 1885-1900/Fergus II
FERGUS II (d. 501), son of Earc, was the first Dalriad king in Scotland. According to the Irish annals, the earliest and best authorities for the Celtic history of Scotland, the Dalriad or Scottish kingdom in Argyle and the Isles, which the mediæval chroniclers and the historians Boece and Buchanan antedated to a fictitious Fergus I, son of Ferchard [q. v.], was really founded by this Fergus, son of Earc. The synchronisms of Flann Mainistreach (i.e. Flann of the monastery of Monasterboice in Louth) state that twenty years after the battle of Ocha the sons of Earc arrived in Britain, and date the battle of Ocha forty-three years after the coming of St. Patrick; 432 being the date of St. Patrick's mission, the migration of the sons of Earc to Scotland would be about 495 or 498 (Skene). The ‘Annals of Tigernach’ substantially agree with this date, having under 501 the entry ‘Fergus Mor, the son of Earc, with the Dalriad race, held a part of Britain and died there.’
The date 501, according to Skene's probable conjecture, refers to the death of Fergus. He and his brothers, Lorn and Angus, came in all likelihood with a small number of followers and took possession of Cantyre and the adjacent isles. The Dalriads were already Christians, having been converted by St. Patrick, and Earc belonged to the royal race of the northern Hy Niall, from which Columba, who followed about half a century later to Scotland, also belonged. The exact cause of the migration from Ulster to Argyle is not recorded, but it was probably due to overpopulation and a desire for more land. Fergus is said to have been succeeded by his son Domangart, and Domangart by his sons Congall I Conall and Gabran Goranus [q. v.]
[Chronicles of Picts and Scots; Skene's Celtic Scotland.]