The monastery was founded in about 520 by Saint Finnian, who initially constructed a single cell at the site. The original site may have been at nearby Ard Relec. According to medieval chronicles, Finnian was led to the site by an angel who told him that it would be the place of his resurrection. Finnian was buried on the site after his death in about 549. During the sixth century, some of the most significant names in the history of Irish Christianity (who would go on to be known as the Twelve Apostles of Ireland) studied at the monastery.