He established a monastery and school in the area now known as Rosscarbery towards the end of the sixth century.
Before establishing the monastic school of Ross, he founded the monastery of Molana on an island in the Blackwater, near Youghal.
In Irish records, he is generally referred to as Mac Mongach (Hairy Child), because he was reported to have been born with his head covered with hair.
The interpretation of this phrase by James Ussher and others as meaning Son of Mongach was rejected by Mervyn Archdall.
[3] The description of Saint Fachtna in Cuimin of Connor's poem on the characteristic virtues of the Irish saints is: Mention is made of Fachtna and Conall of Ros Ailithir within the scholia of the Félire Óengusso in connection with Ciarán of Saigir the Elder who was born and raised on Cape Clear Island.