I was recently invited on an internet radio show, The Black Fridays, to talk about Christianity as it existed in the Pre-Norman period of British history. The title links to the Fridays' webpage, where you can listen to yours truly expound on the topic for a bit. While the information I gave out was sound, I fear I was a little scatter-shot in the approach. It was much more conversational, and less informational, than I might have preferred. So, I thought that I'd give a little outline, more or less, to make things make more sense (if people bother to read this at all).
Despite all the craziness and weirdness that has been published about the Celts in the last few decades, the truth is we really do not know all that much about their indigenous religion. There is a good reason for this; they didn't write things down. It was only after the Christian era that Celtic myths, legends, and stories were compiled by Christian monks, for the reason of preserving them. The Celts are a curious people, though, because of their seeming uniqueness in Christian history. With few exceptions, the Celts converted to Christianity without suffering martyrdoms or conquests. They simply embraced the religion--and it flowered in the British Isles in beautiful ways for centuries.
The indigenous Celtic Church seems to have been, from its beginning, eastern in orientation. Legend has it that St. Joseph of Arimathea brought the Christian faith to Brittania near the time of the destruction of the Jewish temple in Jerusalem in AD 70. These early Christians, many of whom knew Christ and the Apostles, brought with them the Johannine traditions (liturgical and calendrical) that marked them as having continuity with the other communities founded by the beloved disciple. The Celtic Christians also kept to some of the same customs as the Jewish Christians, even into late period, such as the matrilineal descent of kings, and the vocation of priesthood passed down through families.
It is into this world that one of the most famous of the Celtic Christians was born--St. David, who became the Patron of Wales. His mother, St. Nona, was a nun who had been raped by sea-raiding pirates, probably from Ireland. She gave birth to him at the spot known now as St. Non's Well, in modern Pembrokeshire, and a stream of water sprang up from the earth. St. David is connected, also, to the legends of King Arthur; while the sources do not agree on their exact relationship, they all agree that he was a relative of the historical Arthur. Indeed, at least one of the legendary accounts say that he presided at the Mass at Arthur's coronation as King of the Britons. St. David was renown for the strictness of his asceticism, and for his love for his flock. He lived a life of astounding holiness, and was known to have been responsible for the rebuilding of the chapel at Glastonbury--where St. Joseph had first brought the Christian Faith to the Isle centuries before. So strong was the connection between St. David and these early Jewish Christians who came to Brittania seeking refuge from persecution at the fringes of the Roman Empire, that he went on pilgrimage to Jerusalem, where he was consecrated as a bishop. Thus it is that, alone of episcopal sees in the West, the bishops of St. David's could trace their apostolic succession, not to Rome, but to the mother church in Jerusalem at St. James the Just, the brother of the Lord.
The next century and a half following the repose of St. David saw much trouble in the Isles. The Western Empire had fallen; the Legions, that for so long had protected the British Celts, had been recalled to the continent, never to return. Raiders, first from the pagan Irish, then from the Angles, Saxons, Jutes, and Frisians began to pillage the Isle of the Mighty. Then, as the European continent became embroiled in warfare through the migrations of the Goths and the Vandals, these Germanic invaders came to Britain to stay. Eventually, over the next century or so, there were established the Heptarchy--the seven kingdoms of Old England: Wessex, East Anglia, Mercia, Northumbria, Kent, Sussex, and Essex.
After years of struggle with the indigenous Celtic Britons, the Anglo-Saxons kingdoms were, one by one, brought into the Christian fold...mostly through the missionary activities of their Celtic neighbors. Christianity flourished under the Christianized Anglo-Saxon kingdoms until the year 1066.
It was then that William the Bastard (whose good press would later label as "the Conqueror") landed in England, with the backing of the Roman Pope, launching a proto-crusade to bring the local church in Britain firmly under Roman domination, where it was to stay until the English Reformation, which established the English Church as its own entity apart from both the Orthodox and Roman Catholic communions. The systematic repression of the indigenous church in Britain was carried out with exceptional thoroughness; Celtic and Anglo-Saxon churches were demolished, and new, Norman-styled churches were constructed over their ruins. The local clergy were cast from office, and new bishops from Normandy were brought in to replace them. In fact, the last Anglo-Saxon bishop died in 1069, anathematizing the Pope of Rome.
Of the curious links to the Orthodox east, aside from the foundations of the Church in Britainnia with St. Joseph, and the introduction of monasticism from the Egyptian desert fathers, the links to Constantinople, curiously, come precisely through the Scandinavians who caused so much grief during the period of the Heptarchy. The viking trade routes through what is now Russia, with their major center of power being in Kiev, provided a vehicle for Eastern Roman trade and contact to Britain. This is proved by the fact that, in so many of the Anglo-Saxon archaeological finds, the golden byzant, the official coin of the Byzantine Empire, is found more than any other foreign coinage. Indeed, when the last Saxon king of England, Harold Godwinson, was defeated at the Battle of Hastings, his wife and son fled to, of all places, Kiev Rus to live out their days in exile.
Hopefully, this will help you make some sense of the podcast. I hope you enjoy! If you do, please be sure to leave some comments on The Black Fridays' message board.