The explanation for the foundation of a monastery in the centre of the Plains of Mayo in 668 AD. by St. Colman is not to be found locally, but in the ancient English Kingdom of Northumbria. Ancient Northumbria ("North of the river Humber") stretched from southern Scotland to the northern borders of Yorkshire. In the sixth century it was over-run and settled by pagan tribes of Saxons and Angles originating in present-day Saxony in north Germany.
Columba (Columcille in Gaelic) established the Celtic Church in Iona in 563 AD., which quickly spread its influence into Mainland Scotland. In 635 AD., King Oswald of Northumbria sent to Iona for a missionary to convert his people to Christianity. Aidan was chosen for the task and established a monastery at Lindisfarne, near the King's castle at Bamburgh. His mission was successful and the monastery at Lindisfarne flourished. In 660 AD., Colman was appointed Bishop - Abbot of Lindisfarne, following the death of Finian, Aidan's successor. Colman was a native of the west of Ireland and had recieved his education on Iona.
While the Iona "Celtic Church" evangelised Scotland and Northumbria, St. Augustine had established Roman practices in southern England. Both groups were very successful, so much so that the whole of Northumbria became known as the "Cradle of Christianity" throughout Britain.