Everyone knows that St. Patrick converted Ireland to Christianity in the late 5th and early 6th century. What most people do not know is the church he left in Ireland was different than the rest of the church in Europe. The differences are explainable as Ireland was very far from Rome, and travel was not easy. Ireland had never been part of the Roman Empire, and many of the Roman church’s traditions and hierarchies were based on the bureaucracy of Roman government. Where the Roman church was more of a retreat from the sins of the world, the Celtic church was more concerned with living in the world and dealing with local concerns.
Later missionaries from Ireland, such as St. Columba, would travel to Scotland to spread the gospel there. St. Columba set up his base on the island of Iona, which became known as the Holy Island. For over thirty years, St. Columba traveled the wilderness of Scotland founding fifty religious communities and preaching and converting the Scots. Another missionary, Columbanus, took the word of the Celtic church to the pagan tribes in eastern France. He traveled Burgundy founding religious communities and preaching like St. Columba and St. Patrick before him. It was here that the Celtic church first came into conflict with the Roman one. Columbanus refused to submit to the Roman bishops who were already there. They also held the to the traditions of the Celtic church and even rebuked the roman clergy in the area for laxness. No one liked that. This did not stop Columbanus, who in his sixties traveled to the Alps to spread the doctrine of the Celtic church.
So what exactly were the differences between the Roman church and the Celtic church? As previously mentioned, the Roman church placed more emphasis on bishops, whereas the Celtic church managed more at a local level depending mainly on abbots. The two churches also celebrated Easter at different times. The Celtic church called was Paschal, which is closer to the Passover feast Christ was celebrating at the time of the crucifixion, where the Roman church co-opted the name of a pagan feast- Ostare or Easter. The Council of Nice changed the way the date was calculated, but no one bothered to communicate this to the Celtic Church. Ooops. There was also a difference between the way the two churches tonsured, or cut the hair, of the monks. The Roman church used the corona spina tonsure, the shaved circle of hair at the top of the head. The Celtic church used the tonsure of St. John, which was a shaved triangle consisting of a straight line across the back of the head from ear to ear. This doesn’t seem like a big deal to modern readers, but this was quite the fight. The Roman church claimed the circle represented the crown of the thorns and the tonsure of St. John really that of Simon Magnus, a magician Peter bested as a false prophet. The main difference was the Celtic church came from the traditions of Ireland, which was a surprisingly feminist place to live. Brehon law protected women and gave them rights which were unheard of in other parts of Europe. This was not the case in the Roman church.
Roman Christianity was sweeping up through England from Canterbury and Celtic Christianity was moving through England from Ireland and Scotland. They were coming in conflict. Finally, Oswy of Northumbria request a synod to determine once and for all the flavor of Christianity which would dominate the British Isles. The synod was held at Whitby abbey, where his sister Hilda was abbess. Representatives from the Celtic church and the Roman church debated and presented their cases as to why their church was the true one. Oswy was educated in Ireland, but ruled for the Roman church to gain solidarity with the southern kingdoms of Mercia, Wessex, Essex and Kent. After this decision, most of the churches converted to Roman rule, however, there were pockets of resistance up until the ninth century.
England remained staunchly Roman Catholic through the Middle Ages until the Dissolution of the Monasteries under Henry VIII. Even so, Celtic Christianity still survives and is practiced today.
Sources available on request