Yup. Nothing new. Nothing at
Covert Messiah - 19 October 2013 or at
Joseph Atwill's Blog since that date. What a flop.
I must say that I've come across an even weirder conspiracy theory, that it was Constantine who invented Christianity, complete with inserting references to it in older books (
Mountain Man Dot Com).
It's completely possible that there was a historical Jesus Christ who had little resemblance to what comes down to us in the New Testament and elsewhere. Around half a century ago, the Rastafarians of Jamaica turned Emperor Haile Selassie of Ethiopia into a messiah figure.
Historical basis for King Arthur - Wikipedia goes into gory detail.
Arthur Pendragon supposedly lived around 500 CE, complete with supposedly building a sizable empire. But let's see what we have.
He's not mentioned in The Anglo-Saxon Chronicle (~890) or Bede's Ecclesiastical History of the English People (~731), and his first mention of him is in a work attributed to the Welsh monk Nennius around 820. "Nennius" lists 12 battles that Arthur fought as a "war commander" (dux bellorum), and states that he fought alongside "the kings of the Britons" rather than himself being a king.
Nennius is followed by various other chroniclers who mention Arthur, chroniclers who add bits and pieces as they go. The situation changes dramatically in 1136, when Geoffrey of Monmouth wrote his monumental History of the Kings of Britain (Historia Regum Britanniae). It contains not only a detailed biography of Arthur, but also lots of details of the people he associated with, woven together in a complex story. It is the beginning of the familiar form of Arthurian lore.
There's been a lot of argument about who the historical King Arthur had been, and even speculation that he had been entirely mythical. I've done a Lord Raglan scoring of him, and he scores around 14.