Fachtna was born at a place called Tulachteann, and died at the early age of forty-six, probably late in the sixth century, and is buried in his own cathedral church in Rosscarbery, a tuath of which the O'Leary were hereditary lords.
The Annals of Innisfallen (Dublin copy) mark 600 as the year of his death: "Died Fachtna first Bishop of Ross-Ailithre in Corca-Laidhe which goes by the additional name of O'Laeghaire of Ross i.e. Corca Laidhe-I-Laeghaire Ruis".
Returning to his native territory, he set about a more important foundation on a rocky promontory situated in the midst of woods and green fields between two bays.
This was the monastic School of Ross, called in the Life of St. Mochoemoc "magnum studium scholarium", for it quickly became famous for its study of Scripture, and the attention given to all the branches of a liberal education.
More evidence of the extent and variety of the literary work done at Ross is furnished by the geographical poem in the Irish language still extant, composed by MacCosse or Ferlegind, a lecturer at this school.
Joyce said of it: Ross Carbery in Cork, was formerly a place of great ecclesiastical eminence; and it was "so famous for the crowds of students and monks flocking to it, that it was distinguished by the name of Ros-ailithir" [allihir : Four Masters], the wood of the pilgrims.