How separate was the Celtic church?
It is easy to exaggerate the cohesiveness of the Celtic Christian communities. Their members never saw themselves in opposition to the Catholic establishment based on Rome as did the Arians, Priscillianists or the Donatists in North Africa. Even at the height of the conflict between these communities and other Christian groups, they acknowledged the supremacy of the Pope and acquiesced to his specific commands.
On the other hand, these communities did see themselves as separate from their competitors, the Anglo-Saxons. An early Welsh ecclesiastical rule levied penalties for interacting with the English, and for sharing communion with them. When St Augustine attempted to meet with a delegation of seven British bishops on the borders of the domains of Ethelbert of Kent, these bishops refused to talk or even dine with his party; and when Aethelfrith of Northumbria went to battle with Solomon, son of Cynan, king of Powys, hundreds of British Christian monks are said to have assembled to pray for the Venedotian king. It is noteworthy that the British failed to attempt to convert the Anglo-Saxons, and that the successful Celtic missions had come from further away, from the Dalradian Scots.
Differences from the rest of Catholicism
The exact practices by which the Celtic church varied from the rest of Catholicism differ from source to source. It is clear that two points definitely are included in this list:
The Easter Problem
The Easter Problem -- that is, the proper method to be used to calculate the date Easter will fall on in a given year -- is a long and tedious story that extends beyond the topic of Celtic Christianity. As it applies to this topic, the Celtic peoples had lost contact with Rome when Victorius of Aquitania created the tables that were adopted as approved practice in 457. But as they learned of the current practice, the various communities of the Celtic church gradually returned into harmony with the predominant practice: southern Ireland agreed to this at a Synod in 632; northern Ireland at the Council of Birr around 697; the Northumbrian Church at the Council of Whitby in 664; the island of Iona celebrated Easter on the Roman date in 716; and Wales in 768. Various other churches founded or influenced by clerics trained in Ireland or Wales came to celebrate Easter on the Roman date at later times.
Saints of the Celtic church
Prominent individuals associated with Celtic Christianity include Adamnan, Aidan, Brigit, Columba, Columbanus, David, Gildas, Patrick, Piran, and Samson of Dol.
The end of the Celtic Church
Although its impact continued, Celtic Christianity officially ended in 1172 when the Synod of Cashel ended the Celtic Christian system and brought them under Rome.
Celtic Christianity to-day
The phrase Celtic Christianity has come into current used to describe a modern revival of what is believed to be a more spiritually free form of Christianity abandoned after the Synod of Whitby enforced Roman Catholicism as the standard form of Christianity in the British Isles. Many believe that this older worship more closely resembled Eastern Orthodoxy. It is also considered very close to Anglicanism in many respects. Some wags have joked that the amazing thing about Celtic Christianity is that it always somehow manages to perfectly match the expectations of anyone who investigates it.
Celtic Christianity is at present undergoing something of a revival: in the North of England at the Community of St. Aidan and St. Hilda on Lindisfarne, and in Scotland at the Iona Community. It currently embraces both Charismatic and Evangelical Christians, as well as some pagan elements. Celtic Christianity has become increasingly popular in the United States, and an annual conference on the subject is held every year.
Its main features are claimed to be: