Dictionary of National Biography, 1885-1900/Congallus II
CONGALLUS II, CONALL, son of Congallus I, king of the Scots of Dalriada (557–574), according to the chronology of Innes and Skene, is redeemed from the obscurity of the early kings and brought within the pale of history by the brief notice of Tighernach, the Irish annalist, who states the year of his death, and adds that he gave the island of Iona to Columkille (St. Columba). Bede attributes the grant to Brude, the Pictish king, whom Columba visited and converted at his fort on Loch Ness, but the discrepancy is ingeniously, if not certainly, reconciled by the hypothesis of Dr. Reeves, that Conall gave and Brude confirmed the grant as a superior king, or perhaps because Iona lay on the confines of the Pictish territory. On the death of Conall, Columba ordained Aidan, the son of Gabran (the king who preceded Conall), as his successor, apparently in conformity with the law of tanistry. In the year of Conall's death a battle, recorded by Tighemach, had been fought at Delgin in Kintyre, in which Duncan, son of Conall, and many of the kin of Gabran were killed, probably by the Picts, who were endeavouring to crush the rise of the Dalriad kingdom.
[Reeves; Adamnan's Life of Columba; Robertson and Skene.]