Dictionary of National Biography, 1885-1900/Constantine Mac Fergus
CONSTANTINE MAC FERGUS (d. 820), king of the Picts, acquired the monarchy by the defeat of Conall Mac Taidg (Teige), who was assassinated in 807 by another Conall, son of Aidan, a Dalriad king in Kintyre. After this date there is a blank in the Irish annals of the names of any separate kings of the Dalriad Scots, and Mr. Skene conjectures that Constantine ruled over them for some years (Celtic Scotland, i. 302). The reign of this monarch was the era of the first advent of the Norsemen, who in 793 attacked Lindisfarne, the holy island on the east coast of Northumbria, and almost simultaneously the Hebrides, in 794 according to the ‘Annals of Ulster.’ In 801, and again in 806, Iona was ravaged by them, their object at this period of their raids being to spoil the monasteries. The plunder of Iona and the slaughter of the monks led to the removal of some of the relics to Kells in Meath, and of others to Dunkeld, where Constantine founded a monastic church. He died in 820, and was succeeded by his brother Angus. Constantine has usually been deemed the last of the Pictish kings, but the recurrence of his name in three monarchs of the united kingdom of the Picts and Scots, the fact that Donald, son of the first of these Constantines, is the first king called ‘Ri (king of) Alban’ in the Irish annals, while his predecessors are called kings of the Picts (with the exception of Kenneth Macalpine, who is denominated the first of the Scots who ruled in Pictavia), appear to justify Mr. Skene's hypothesis that Pictish blood still continued to flow in the veins of the sovereigns of the united monarchy, probably through their mothers. If so, it appears to follow that the statement that the Picts were almost exterminated by Kenneth is an exaggeration, and the union may have been of a more pacific character than is often supposed. But all this belongs to the dark period of hypothesis and conjecture in Scottish history. The name of Constantine, of which Constantine Mac Fergus is the first bearer, is remarkable, and, being equivalent to no known Celtic word, it would seem to have been adopted, perhaps at baptism, in imitation of the great emperor, as that of Gregory may have been taken from the great pope.
[Robertson's Scotland under her Early Kings; Skene's Celtic Scotland.]