Ciarán of Clonmacnoise (c.512–545) was the founder of the greatest monastic establishment of early Christian Ireland after Armagh. The Latin and Irish Lives of Ciarán have been taken to derive from a ninth-century recension kept at Clonmacnoise, their historical value for the life of a sixth-century figure being therefore suspect. They relate that he was born of an ordinary family, the son of a journeyman carpenter or wright named Beodán (Beonáed, Beoán), ‘of the Latharna’, i.e. of Dál nAraide in Ulster – hence Ciarán's epithet mac an t-sáir (son of a wright). His mother is named Darerca, a daughter of Ercán, of the Ciarraige of Irluachair. He was baptised and fostered by the deacon Diarmait.
Ciarán is said to have begun his studies under Finnian (qv) of Clonard; he took along a cow to supply himself with milk – the famous ‘dun cow’, the skin of which was supposedly devoted to Lebor na hUidre, one of the relics of Clonmacnoise. Afterwards he went to Énnae (qv) of Aran to continue his monastic training and was ordained a priest. He later spent some time with Senán (qv) of Inis Cathaig (Scattery Island, Co Clare). His first foundation was Inis Aingin in Lough Ree (near Athlone, Co. Westmeath). He surrendered the foundation, however, and in January 545 he founded Cluain moccu Nóis (‘the meadow of the sons of Nós’: Clonmacnoise), on the east bank of the Shannon below Athlone. This was to be his last and greatest foundation, the ‘place of his resurrection’. Ciarán lived but a short time after: he died on 9 September of that year.
Clonmacnoise went on to become one of the wealthiest and most important of Irish monasteries, to which its impressive ruins now bear witness. It became one of the chief centres of learning in the country, noted especially for its cultivation of vernacular Irish literature. The Annals of Clonmacnoise, the Annals of Tígernach (Tigernach Ua Bráein (qv)), Lebor na hUidre, and the first twelve folios of Rawlinson B. 502 were all compiled there. The enshrined crosier believed to be that of Ciarán and that known as the crosier of the abbots of Clonmacnoise are preserved in the National Museum of Ireland. Because of its wealth and importance Clonmacnoise was raided several times by the vikings and the Irish. There is a complete list of the abbots of Clonmacnoise, which is of considerable historical value.
The prologue to the Martyrology of Óengus (qv) (fl. c.830) describes this monastic city thus: ‘Choirs lasting, melodious, around Ciarán . . . with the victorious tumult of great Clonmacnoise’. His feast-day on 9 September is found in the ninth-century Martyrology of Usuard and in the Reichenau manuscript of the Martyrologium Hieronymianum. His various Latin Lives have some historical value. A monastic rule of some severity, a penitential litany, and two spiritual poems are ascribed to Ciarán, but it is unlikely that he was the author of any of these works.