1.The Church didn’t fully apostatize till 570 AD
2.The last vestige of priesthood authority was in Brittan in the Celtic Church.
3.There was a war of ideas between the Roman and Celtic Church.
4.The Legendary Arthur was alive at this time and may have tried to save Brittan and the Church.
Since there is a lot of information here I will post it in chapters.

The loss of the true faith in Britain- an abomination that led to desolation
Celtic Christianity: part 1 of 3
Introduction
After the deaths of the apostles the Church of Jesus Christ drifted into apostasy. Churches had been set up throughout the empire, but one by one they all fell under the power of the "little horn". Some parts came under the control of the horn sooner than others. The church in Britain was perhaps the last to be defeated.
The horn probably represented Europe. Its power was both political (the "fierce appearance" of the invading barbarian kingdoms) and religious (the "mouth speaking great things" - apostate Christianity). When we look at how these forces affected the British church, we can see more clearly how the apostasy happened.
The Ancient Apostles in Britain
The first missionaries
The sixth century British historian Gildas said the gospel came to Britain at a very early stage - in the last year of Tiberias, AD 37 (perhaps as a result of the scattering described in Acts 8:1-4). For this and other references in this section, see "Saint Joseph of Arimathea at Glastonbury" by Lionel Smithett (London: Mowbray & co., 1922).
The Seventy
Aristobulus (according to Strong's Concordance) was one of the Seventy. He may have been Peter's father-in-law. Several sources (Hippolytus writing in AD 160, the Martyrologies of the Greek Church, and others) state that he preached the gospel in Britain. He is only mentioned in the Bible in passing, in Romans 16:10)
The Apostles
Latter-day Saints will be familiar with Joseph Smith's claim that ancient prophets walked the British Isles. This may be confirmed by the great church father Eusebius, who stated that Apostles did come to Britain. According to Doretheus (bishop of Tyre, writing in AD 303), the apostle Simon Zelotes was crucified in Britain.
It may be interesting to note that Bruce R. McConkie, following the writings of Edersheim (1:521-22) indicates that Simon Zealots may have been a cousin of Christ through on Joseph's side. (The Mortal Messiah, Vol.2, footnotes, p.113)
Aristobulus, mentioned above, traditionally worked under Paul. Clement of Rome (AD 30 to 100) states that, before his martyrdom, Paul went "to the extremity of the west". Theodoret (writing in AD 435) and others say that Paul came to Britain.
Joseph of Arimathea - and the Lord himself?
Some people make great claims for the importance of Britain in early Christianity. These are discussed elsewhere.
Whatever the truth, there is plenty of evidence that the church in Britain, these "Isles of the sea", could trace its authority to Christ, through the apostles, without going through Rome.
AD 166-380: The Influence of the church of Rome
When the apostles died, the churches began to be tossed
Since Rome had more political power, weaker churches tended to look to her for support. Even Britain may not have been immune. As early as the year 166, the British king Lucius allegedly asked the Roman bishop Lucius to send missionaries to baptize him. However, other scholars reject this, and say that Lucius simply asked for one of the British saints at Rome to do the job.
Later history indicates that there must have been increasing tension between the British church and what Rome was becoming. But just as the second century in the empire is suspiciously lacking in records (Nibley refers to it as "when he lights went out"), so the period from the late second century to 380 is a blind spot in British church history. Commenting on the alleged discovery of a fragment of the cross, recorded in the Anglo-Saxon Chronicle for the year 199, a later footnote to the Chronicle adds:
"This and other notices of Ecclesiastical matters, whether Latin or Saxon, from the year 190 to the year 380 . . . may be safely considered as interpolations, probably posterior to the Norman Conquest [1066]".
So the victors were re-writing church history.
The Year 381: the Great Battle Against the Little Horn
The Anglo-Saxon Chronicle was a history of Britain written before by the Angles and Saxons, the Germanic tribes who conquered Britain in the period in fifth and sixth centuries. It says the following about the year 381:
"This year Maximus the emperor obtained the empire; he was born in the land of Britain . . . [there follows a few words about how he replaced Gratian]. In these days the heresy of Pelagius arose throughout the world."
That was the Saxon (German) view. But who were Maximus and Pelagius, what exactly did they do, and why did they do it?
The Britons in 381
The Britons could no doubt see how the church was declining throughout the empire. They could see the invading barbarians (from firsthand experience of the Scots and the Picts). They could see the church subtly changing and distorting the doctrines of Christ. In the 380s they launched an audacious double attack on the European monster. Two powerful men arose from Britain who may had the strength to turn the tide. The first, Maximus, might have stopped the advance of the Germanic tribes. The second, Pelagius, might have stopped the decay in Christianity.
Maximus - battling to save civilization
The late fourth century was disastrous for the Roman Empire. In 376, the emperor Valens allowed the Visigoths to settle inside the empire. Valens was soon replaced by an even weaker emperor - an eight year old boy called Gratian. Gratian then chose an assistant emperor - the four year child Valentinian!
They could not halt the Visigoth advance. (The Visigoths eventually sacked Rome in 410). The British knew that their culture (and with it their already weak church) could not survive if the barbarians won. Even apart from his military losses, Gratian was heavily influenced by St Ambrose, and was giving more and more concessions to the Roman church. The British knew they had to do something.
At that time, Magnus Maximus commanded the Roman troops in Britain. He was (according to Bede) capable and courageous. He was British (or possibly Spanish), of humble origins, and thus not infected by the madness of Rome. The British troops saw their chance. Maximus was declared emperor. He soon gained the support of Gratian's advancing troops, but unfortunately Gratian turned and ran, and was killed by Andragathius. Maximus then made a truce with Valentinian. In 384 Theodosius agreed to allow Maximus to rule the western part of the empire. But sadly we will never know what Maximus might have achieved. Theodosius did not like sharing power. He eventually defeated Maximus in 388, and the empire continued to decline. Rome was sacked 22 years later, and 66 years after that the last western emperor was deposed by the Ostrogoths.
A note about Gildas' history.
Some readers may notice that later historians, including Gildas, looked on Maximus as a villain. This is all part of Gildas' fatal flaw - taking the Roman view of history as the truth. Modern historians agree that, when writing about events before his birth (or the birth of his father's generation), Gildas was extremely unreliable. It is my belief that, in rejecting the Celtic view in favor of the Roman view, Gildas himself may have lost the last thread of early Christianity. Hence the early church died when Gildas died, in 570.
Pelagius - battling to save the truth
Pelagius came from Britain to Rome in 380. He was an extremely able preacher and was greatly respected because of his high standards. He saw that the doctrine of being saved purely by grace was leading to the church becoming lazy and corrupt. He dedicated his life to showing by word and example that good works were needed. He attacked false teachings like "original sin".
"The rigorous asceticism of his adherents acted as a reproach to the spiritual sloth of many Roman Christians, whose moral standards greatly distressed him. He blamed Rome's moral laxity on the doctrine of divine grace. . . Pelagius attacked the teaching on the grounds that it imperiled the entire mortal law and soon gained a considerable following in Rome." (-Britannica).
Pelagius was strongly opposed by Augustine, the architect of medieval "Christian" doctrine. This was the great battle of the late fourth and early fifth century: Augustine (infant baptism, predestination, good works are not essential) versus Pelagius (baptism of believers, we are free to choose, good works are essential). Despite the fact that a synod in Jerusalem could not find anything in the scriptures to censure him, Pelagius was finally silenced. Augustine won.
AD 429-447: The Counter-Attack
The church of Rome was very concerned about these "Pelagian" beliefs in Britain. It sent the very capable Germanus (an appropriate name given that the other great threat came from the Germanic invaders) to sort things out. Germanus arrived in 429 (according to Bede), and was a powerful preacher of the Roman version of Christianity.
The same year he arrived (429) he had many great successes. He managed to suppress or change much of the British "Pelagian" faith. He set up schools to ensure that new priests were taught in the Roman way. He left and only returned in 447 when he heard reports that some people were returning to their previous Christianity. But when he arrived he found that actually "but few had gone astray".
But why had any gone "astray"? Why had some of the Britons rejected the new Roman Christianity? Because, quite simply, accepting the Roman ways was causing the British nation to slip into sin. This was exactly what Pelagius had been trying to prevent.
An Abomination that led to Desolation
Several times in the Bible we read of abominations that lead to desolation. The phrase refers to times when the church commits abominations (usually involving false gods) and consequently the land is left desolate. The first and biggest example is the fall of Israel to the Assyrians (discussed here). Another example was the fall of Jerusalem to the Roman armies (foretold in Matthew 24 and elsewhere). Daniel uses the phrase more than once in his prophecies. And British history gives us another example.
The abomination
Pelagius (from the British faith) was closer to the truth that Germanus (of the Roman tradition). Pelagius reacted against the sinfulness of Rome, and taught the need for good works, and other issues such as saying that infant baptism was wrong. But the British people rejected Pelagius in favour of Germanus. They were giving in to the false teachings of Roman Christianity.
Britain before Germanus: repentance and prosperity.
Readers of the Book of Mormon will be familiar with the classic cycle of national decline, where hardship is followed by humility and repentance. This righteousness is followed by prosperity. This leads to pride, then destruction. Fourth century Britain illustrates this quite neatly.
Describing the period 400-414, Bede records how the invading Picts and Scots had reduced Britain to a sorry state of war and famine. The chronologically next chapter covers 426 to 447, when the Britons drove out the invaders:
"When, however, the ravages of the enemy at length ceased, the island began to abound with such plenty of grain as had never been known in any age before"
He does not make the link explicit, but a later chapter indicates that this was exactly the time when the faith taught by Pelagius had taken hold. (Chapter XVII records how Germanus was sent in 429, because "some few years before their arrival, the Pelagian heresy... had sadly corrupted the faith of the Britons").
The influence of Germanus
Germanus arrived in 429 and had almost immediate success:
"The apostolic [i.e. Roman] priests filled the island of Britain with the fame of their preaching and virtue; and the word of God was by them daily administered, not only in the churches, but even in the streets and the fields, so that the Catholics were everywhere affirmed, and those who had gone astray, corrected."
Chapters XVII to XX of Bede (book 1) record the great success of Germanus. When Germanus returned to Britain in 447, "They found the people constant in the faith as they had left them, and ...but few had gone astray". So what was the result of the Roman faith having such great success between 429 and 447?
Britain after Germanus: pride and wickedness.
The following is Bede's description of the period 426 to 447, when the teachings of Germanus are taking hold. It follows on from the famine in 414, the increasing influence of Pelagius' call to repentance, and the national prosperity.
"with plenty luxury increased, and this was immediately [during the teachings of Germanus, though Bede will not make the connection] attended with all sorts of crimes; in particular, cruelty, hatred of truth, and love of falsehood; insomuch, if any one among them happened to be milder than the rest, and inclined to truth, all the rest abhorred and persecuted him, as if he had been the enemy of the country [exactly the treatment Germanus' followers gave to the Pelagians].
"Nor were the laity only guilty of these things, but even our Lord's own flock, and his pastors also, addicted themselves to drunkenness, animosity, litigiousness, contention, envy, and other such like crimes, and casting off the light yoke of Christ."
Remember that Pelagius' teachings had been motivated by the shocking wickedness of Rome, which he directly linked to their belief that good works were not essential. Now Pelagius had been defeated and Rome had won. And sure enough, the British became like Rome.
The desolation that followed these abominations
To quote Bede (Ecclesiastical History, book I chapter XV):
"In the meantime, on a sudden, a severe plague fell upon that corrupt generation, which soon destroyed such numbers of them, that the living were scarcely sufficient to bury the dead ... not long after, a more severe vengeance, for their horrid wickedness, fell upon the sinful nation ..."
Vortigern, chief of the Britons, did just what the Roman emperor Valens had done a generation before. He invited in the Germanic tribes (in this case the Angles) to defend the country. Instead, the Saxons, with their allies the Angles, were far worse than the Scot and Picts had been.
"having on a sudden entered into league with the Picts, ...they began to turn their weapons against their confederates. ... the barbarous conquerors ... spread the conflagration from the eastern to the western sea, without any opposition, and covered almost every part of the devoted island. Public as well as private structures were overturned; the priests were everywhere slain before the altars; the prelates and the people, without any respect of person, were destroyed with fire and sword ...
"Some of the miserable remainder, being taken in the mountains, were butchered in heaps. Others, spent with hunger, came forth and submitted themselves to the enemy for food, being destined to undergo perpetual servitude, if they were not killed even upon the spot. .. Others, continuing in their own country, led a miserable life among the woods, rocks, and mountains, with scarcely enough food to support life, and expecting every moment to be their last."
So it was that the land of the Britons was laid desolate. The land was given a new name. England - the land of the Angles.
"In short, the fire kindled by the hands of these pagans, proved God's just revenge for the crimes of the people; not unlike that which, being once lighted by the Chaldeans, consumed the walls and city of Jerusalem." - Bede, book 1, chapter XV.
Very little of the "Christian fabric" survived
This not only destroyed the land, but the church as well. According to the history of the church at http://abbey.apana.org.au/history/" onclick="window.open(this.href);return false; :
"The material achievement of the Roman rule [in Britain] was largely destroyed, and with it a great part of the Christian fabric too. St. Gildas, writing a century and more after the events he describes, hands on a tradition of churches destroyed, of priests massacred, of loot and sacrilege, and of a wholesale flight of the survivors."
Thus, only a handful of the original Christians survived in Britain into the sixth century. The next page looks at how every last remnant was wiped out by the year 570.
the bottom line
Long ago Britain had true Christianity. How it was lost is a story of heroism and tragedy.
http://mormonprophets.org/prophecies/ce ... nt-britain
The reason I started this thread is I just began reading Jack Whyte’s “The Camuloud Chronicles” who put historical research into the legend of King Arthur without the magic. I enjoy historical fiction and so far Whyte’s is the closest to what I have imagined as what may have given birth of the Arthurian legends.