Carthach (Lat. Carthagius) is the name of two early Christian saints.
1. The Elder, commemorated March 5, is entered in the Marst. Talclight as "Carthach mac-Aeingusa Droma Ferdaim," and in Mart. Doneg. as bishop, alumnus of Ciaran of Saighir. Colgan (Acta Sanctorum, p. 473- 476) gives a memoir from what little is known of him. He was of royal descent in Mullnter, being son or grandson of Aengus, king of Cashel. He was sent by St. Ciaran upon a penitential pilgrimage, when he spent seven years abroad, visiting Gaul and Rome. On his return he taught, and founded churches and monasteries, St. Ciaran choosing him, it is said, to be his successor. The scene of his labors was Kerry, where he was bishop; he had a church called Druim-Fertain, in Carberry; another on Inis-Uachtair, in Loch Sileann, now Sheelin; and a third, Cill-Carthach, in Tir-Boghaine, in Tirconnel, County Donegal. In Kerry, on the banks of the Mang, he trained his pupil and namesake, St. Carthage the younger. The year of neither his birth nor his death is known, but he flourished about A.D. 540, and probably did not die before 580. His two chief designations are "alumnus S. Kierani Sagirensis," and "institutor S. Carthacii Junioris sen Mochudse" (see Lanigan, Eccl. Hist. 2, 2, 98 sq.; Kelly, Cal Ir. Sanctorum, p. 83). The Bollandists (Aeta Sanctorum, Mart. 1, 389-399) have a combined account of St. Kieran and St. Carthach.
2. The Younger, commemorated May 14, is one of the most noted saints in the beginning of the 7th century. Two lives are given by the Bollandists (Actas Sanctorums, May 14, tom. 3), the second life being the most historical There is also a Life of St. Carthage in the so-called Book of Kilkenny, in Primate Marsh's Library, Dublin. He was a native of Kerry, and for forty years ruled his community of monks in Rahen of Ballycowlan, King's County, where scholars flocked to him from all parts of Ireland and Britain, so that he is said to have had eight hundred and sixty-seven under him. He had been ordained priest by the elder St. Carthach, perhaps about 580, and at Iahen, which was probably founded in 591, and was consecrated bishop. For his monks he drew up a rule, but, notwithstanding his sanctity and zeal, he was driven from Rahen by Blathmac, king of the country. His expulsion from Rahen, "in diebus pasche" is usually set down at 630; the Four Masters give 631, and the other Irish annals place it later. After wandering about for some time he was at last presented with land for a monastery, by Metris, which was the origin of the present church and town of Lismore. St. Carthach had only been a short time at Lismore when he died, May 14, 637, and was buried in the monastery.