Our holy Father Constantine was, according to one tradition, the nephew of the famous King Arthur, to whom the latter bequeathed his crown when he was mortally wounded.
According to another, he was a king of Cornwall who abandoned his kingdom and became a monk in St. David's cell. Then, leaving for another land, he built a monastery there.
The fullest traditions concerning him come from Scotland. They state that he was the son of Paternus, king of Cornwall, and married the daughter of the king of Brittany. But she died, and he, grieving over her death and refusing to be comforted, delivered his kingdom to his son, and bidding farewell to all, left his kingdom and crossed over to Ireland.
Coming to a certain monastery, for seven years he worked humbly carrying grain to and from the monastery mill. One day he was sitting in the mill and said to himself; "Am I Constantine, king of Cornwall, whose head has so often worn the helmet and his body the breastplate? No, I am not." A man who was hiding in the mill overheard this and reported it to the abbot.
He then took him away from the mill, educated him, and raised him to the priesthood. Soon after this, he left the monastery and went to St. Columba; and afterwards he was sent by St. Kentigern, the bishop of Glasgow, to preach the word of God in Galloway, in South-West Scotland. There he was elected abbot of a monastery, where he lived a holy life until old age. According to another tradition, he founded a monastery at Govan on the Clyde. In his extreme old age, St. Constantine prayed God to give him a martyr's death, and he heard a voice from heaven saying that it should be as he had asked. Then he went preaching the word of God throughout the land, and came eventually to the island of Kintyre. There some evil men followed him, and, coming up to his attendant, they cut off his hand. The saint immediately healed him with a touch.
Then the evil men showered blows upon the saint, cut off his arm, and left him for dead. Calling the brethren to him, the saint comforted them with spiritual words. Then he fell asleep in their presence.
St. Constantine was martyred, according to the Scottish tradition, in 576, and according to the Irish tradition in 588.
His feast day is March 9 in Wales and Cornwall, March 11 in Scotland and March 18 in Ireland.
Source: http://en.wikipedia.org/wiki/Saint_Donnan
