St. Ninian

From Bede's History of the English Church and People, Bk. III, ch. 4:

IN the year of our Lord 565, when Justin, the younger, the successor of Justinian, had the government of the Roman empire, there came into Britain a famous priest and abbot, a monk by habit and life, whose name was Columba, to preach the word of God to the provinces of the northern Picts, who are separated from the southern parts by steep and rugged mountains; for the southern Picts, who dwell on this side of those mountains, had long before, as is reported, forsaken the errors of idolatry, and embraced the truth, by the preaching of Ninias, a most reverend bishop and holy man of the British nation, who had been regularly instructed at Rome, in the faith and mysteries of the truth; whose episcopal see, named after St. Martin the bishop, and famous for a stately church (wherein he and many other saints rest in the body), is still in existence among the English nation. The place belongs to the province of the Bernicians, and is generally called the White House, because he there built a church of stone, which was not usual among the Britons.

Bede's History of the English Church and People