Mac-Caírthinn (d. 506), bishop and disciple of St Patrick (qv) and founder of the church of Clochar (Clogher, Co. Tyrone). Nothing is known of his ancestry other than that the Uí Maicc Caírthinn were one of the septs of the Airgíalla (in Co. Londonderry), which suggests that he was of northern origin. One genealogy states that he was the son of Cainnech, a descendant of Bresal son of Brión. Another claims that he was a son of Darerca, sister of St Patrick, and was baptised by Patrick at Druim Lias – Darerca is credited with being the mother of a number of other early ecclesiastics including Lommán of Trim, Mac-Caille (qv) and Mel (qv). In some sources Mac-Caírthinn is called the ‘champion’ of Patrick, whom he accompanied and assisted in old age; he is also listed among the ‘four-and-twenty persons who were in orders’ with Patrick. According to tradition, Patrick entrusted him with the gospel manuscript known as the Domnach Airgit (Royal Irish Academy MS 24 Q 23; probably eighth century). The manuscript was later preserved in a silver and gilt shrine, now in the National Museum of Ireland.
The ‘Collectanea’ (§16.1) of Tírechán (qv) mentions one filius Cairtin, who was supposed to be a maternal uncle of St Brigit (qv) and was in charge of the church of Ráith Dallbrónig (in the barony of Dunboyne, Co. Meath). In the ‘Additamenta’ in the Book of Armagh the same filius Cairtin is credited with making a grant of land to Patrick somewhere in the present Co. Leitrim or Co. Sligo (§8). It is likely that these references are to Bishop Mac-Caírthinn. The tract in the Book of Leinster on the alternative names of Irish saints says that Mac-Caírthinn was also known as ‘Fer-dá-Chrích’. This name which means ‘man of two districts’ was accorded to a number of distinguished ecclesiastics. In Mac-Caírthinn's case, it became a source of confusion. Both the Martyrology of Óengus (qv) (fl. c.830) (15 August) and the Martyrology of Donegal (6 October) mistook him for Fer-dá-Chrich (qv) (d. 748), abbot of Dairinis in west Co. Waterford.