This date is also supported by his position in the Irish genealogies and by the Life of Saint Mogue (born c.560), who was taught by Caillín.
[1] Caillin's mother's name was Dediva (also called Editua or Dedi or Deidi or Deighe or Deidiu or Deaga), daughter of Tren, son of Dubhthach moccu Lughair, who was Chief Ollam of Ireland and royal poet of King Lóegaire mac Néill.
At the end of a long period of study in Rome he returned, bringing with him relics of the apostles and a cloth made by the Virgin Mary and used when she fed the infant Jesus.
According to the Book of Fernagh, Caillin returned to Ireland twelve years after the arrival of Patrick, who later consecrated him bishop.
[2] He founded a monastic site at Fenagh, County Leitrim, which was then the territory of the Conmhaícne Magh Rein, part of the overkingdom of Breifne.
Fenagh was celebrated for its school which students from all over Ireland and Europe came to study, among whom was Saint Mogue of the neighbouring parish of Templeport.
Its importance we may judge from the story that claims many of Irelands Kings are buried in the ancient graveyards adjoining the Abbey.
Caillin is said to have helped his brother Senchán Torpéist to recover the lost tale called Táin Bó Cúailnge.
[3] His pedigree is given as follows: The family name Mac Giolla Chaillín means (son of) devotee of St. Caillin.