For the Cornish king of the same name see King Cadoc
Saint Cadoc or Cadog, Abbot of Llancarfan, was one of the 6th century Welsh saints whose life touched King Arthur. The Abbey of Llancarfan, near Cowbridge in Glamorganshire, which he founded circa 518, became famous as a centre of learning. The prefix of his name means 'battle'.
Cadoc's story appears in the Buchedd Cadog (or 'Life of Cadoc') written by Lifris of Llancarfan in circa 1100. It is of limited historical merit, but some details are of interest. He was a son of Gwynllyw (Latinized Gundleus), King of Gwynllwg in South Wales, a brother of Saint Petroc, but a robber chieftain who led a band of 300. His mother, Gwladys (Gladys) was the daughter of King Brychan of Brycheiniog who had been abducted in a raid, during which King Arthur acted as peacemaker. Cadoc's father later stole the cow of the Irish monk, St. Tathyw, and, when the monk came courageously to demand its return, the King decided in return to surrender his son to his care. Cadoc was raised at Caerwent in Monmouthshire by Tathyw, who later became a hermit.
In adulthood, Cadoc refused to take charge of his father's army, preferring to fight for Christ instead. He proselytized over a large area of Wales and Brittany. He built himself a hermitage at Llancarfan (now in the south of Glamorgan) that soon grew into a monastery, one of the most important in Wales where many holymen were trained. There was another foundation at Llanspyddid (3km W of Brecon), and he is credited with the establishment of churches in Dyfed, Cornwall and Brittany. About 528, after his father's death, he is said to have built a stone monastery in Scotland below 'Mount Bannauc' (generally taken to be the hill SW of Stirling down which the Bannockburn flows). It has been suggested that the monastery was where the town of St Ninians now stands, 2 kilometers south of Stirling. Cadoc went on pilgrimages to both Jerusalem and Rome and was distressed that the Synod of Llanddewi Brefi was held during one of these absences. He came into conflicts with kings Arthur, Maelgwn of Gwynedd and Rhain Dremrudd of Brycheiniog. At one time, he apparently lived as a hermit with Saint Gildas on an island in the Bay of Morbihan, off Vannes in Brittany. There are chapels dedicated to him at Belz and Locoal-Mendon in Morbihan and at Gouesnac'h in Finistère, where he is called upon to cure the deaf. His name is also the basis of some thirty Breton place-names.
Cadoc later moved on to 'Beneventum'. Beneventum is not firmly identified. It is variously suggested as Benevento in Italy or, perhaps more likely, the Roman town of Bannaventa (5 kilometers east of Daventry in Northamptonshire) on the edge of Saxon territory in Britain. This latter hypothesis proposes that it was overrun by Saxons at this time, thus explaining both the killing of Cadoc and the prohibition on Britons entering the town to recover his body.
Cadoc, with Illtud, is one of the three knights said to have become keepers of the Holy Grail. At Caerleon, a Roman centre of Monmouthshire, the much-rebuilt church dedicated to St Cadoc, though of Norman origin, stands on the foundations of the Roman legion headquarters, a sign of the Christianization of Roman sites after the legions departed Britannia. It may memorialize an early cell of Cadoc's, although an old tradition suggests that, in this case, Cadoc is a corruption of Cadfrod.
See also:

Cambuslang