Cellach (Celsus) (d. 1129), bishop and abbot of Armagh, was one of the first of the reforming clerics of the Irish church in the eleventh century. He was a member of the Clann Sínaig family, which had held the abbacy of Armagh since c.965. He was son of Áed, grandson of Máel-Ísu, and a brother of Niall (qv) (d. 1139), who held the position of lay-abbot of Armagh for some years in the 1130s. Cellach had succeeded his granduncle Domnall (qv) (d. 1105), who had in turn succeeded his elder brother Máel-Ísu (d. 1091). The Annals of Ulster record that ‘Cellach . . . was appointed in his [Domnall's] place to the successorship of Patrick [St Patrick (qv)] by the choice of the men of Ireland and he received orders on the feast-day [23 September] of Adomnán [qv]’.
In the following year, 1106, Cellach was consecrated as ‘noble bishop’ (uasal epscop) in Munster ‘by command of the men of Ireland’, following formal circuits of Cenél nÉogain and Munster as coarb (successor) of Patrick and receiving his ‘full due’ of tribute. He subsequently revisited Munster in 1120. He also visited Connacht (1108, 1116) and Meath (1110). The implication is that his appointment as bishop of Armagh gave him a position of pre-eminence in the Irish church, before the actual establishment of a diocesan hierarchy in 1111. It is probable that his consecration was assisted by Máel-Muire Ua Dúnáin (qv), first papal legate to Ireland and ‘chief bishop of Munster’, and that it took place at Cashel.
His consecration as bishop ended a tradition of lay-abbots at Armagh and would, with the election of Malachy (qv) to the see in 1134, also end the lay-governance of the Clann Sínaig family, which Cellach himself, as a reforming bishop, had wanted to abolish. It was but part of Cellach's plan for reform of the Irish church which was then gaining momentum – for example, the newly-created Norse-Irish bishopric of Limerick chose and consecrated its own candidate, Gilbert (qv), in 1106/7, rather than, as hitherto, sending the chosen candidate to Canterbury. Again, after the death of Bishop Samuel Ua hAingliú (qv) Cellach temporarily occupied the Norse-Irish see of Dublin (c. 1121–2), despite the fact that the dissenting party had dispatched Gregory (qv) to Canterbury for consecration. The Annals of Ulster (1121) describe the episode thus: ‘Cellach took the bishopric of Áth Cliath by choice of the foreigners and of the Gaedhil.’
Apart from his normal administrative duties, Cellach, as coarb of Patrick, played a peace-keeping role on a number of occasions (1107, 1109, and 1113) in the incessant dynastic wars between the southern claimant to the high-kingship, Muirchertach Ua Briain (qv), and his northern opponent, Domnall Ua Lochlainn (qv), and between other warring kings on subsequent occasions. His predecessor Domnall had performed the same function. An annal for the year 1126 (‘There was a storm of great war in Ireland, so that it was necessary for the coarb of Patrick to be a month above a year abroad from Armagh making peace among the men of Ireland . . .’) indicates that one of Cellach's last departures from Armagh was for the purpose of acting as peace-maker.
In 1111 Cellach was present at the general synod of Ráith Bressail, near Cashel, which was presided over by Gilbert the papal legate and held under the protection of Muirchertach Ua Briain. The main outcome of the synod was that Ireland was divided into twenty-four diocesan sees north and south, Armagh and Cashel being confirmed as the primatial sees. Cellach's exact function at this reforming synod is not known, but the annals suggest that he played a key role in convening and organising it. In 1119 he ordained Malachy as priest, having ordained him deacon the previous year; he almost immediately made him his vicar, as Bernard of Clairvaux relates. Finally, in 1124, he consecrated Malachy as bishop and appointed him to the see of Connor. Clearly, Cellach believed that Malachy would continue the reform movement after his death. The record suggests that Cellach did not abuse the wealth and privileges of his office; the tribute which he collected on his cuarta (visitations) through the provinces seems to have been devoted to the re-roofing of the great church of Armagh (AU 1125), to the building of the new church of Saints Peter and Paul (1126), and to gifts to other churches.
The somewhat grandiloquent entry in the Annals of Ulster for the death of Cellach on 1 April 1129 states that he died at Ardpatrick in Munster and that he was buried ‘with honour in the tomb of the bishops’ in Lismore on 4 April. The reason for his absence from Armagh may have been that he was visiting his chosen successor Malachy, who in 1127 had taken refuge in Munster with some of his disciples after the destruction of his new monastery at Bangor in a local war. Cellach's wish to be buried at Lismore reflects his kinship with Máel-Ísu Ua hAinmire (qv) (d. 1135), bishop of Lismore, and his desire to rest in the place where the reform of the Irish church may truly be said to have begun. Bernard of Clairvaux describes Cellach as ‘a good and devout man’ (cap. 4, §20); it is regrettable, however, that there is no contemporary biography of him, as there is of Malachy. The chief sources for Cellach's life are the annals, especially the Annals of Ulster, and Bernard of Clairvaux's Life of Malachy, which contains numerous references to his spiritual nurturing and sponsorship of Malachy.