Geoffrey of Monmouth was born Geoffrey ap Arthur was born around 1100AD. He was the nephew of the Bishop of Llandaff a position he later held himself. He lived in Oxford from 1129 - 1151, after which he moved to London, becoming Bishop of St. Asaph in Wales, which he never visited. He died in 1155. Geoffrey wrote his 'History' while he was at Oxford finishing it around 1136. Geoffrey of Monmouth's 'History of the Kings of Britain' was a medieval bestseller. There are around 215 surviving manuscript copies from before 1155.

The History of the kings of Britain

"The much-maligned Geoffrey of Monmouth, Archdeacon of Monmouth and later Bishop of St.Asaph's, first popularized King Arthur's story, around 1139, in his "History of the Kings of Britain". Though he was writing some six hundred years after Arthur's death, there is no reason to suppose that Geoffrey's history was "made up...from an inordinate love of lying" as both contemporary and modern historians almost universally insist. Geoffrey claimed he had taken most of his information from an earlier British source, unknown to us today: and why not? The early portion of his history clearly relates the mythology of the Celtic peoples and the stories of their Gods, whom his source had turned into early Kings: Bladud, Leir, Belenus, Brennius and so on. Later, however, he turns to real history. From the time of Julius Caesar's invasion of Britain in 55 BC, which both Geoffrey and the great man himself relate at great length, we can no longer be sure that the Archdeacon is reciting mere legend. Much of his information has corroborative historical sources like this. Who is to say that everything he tells us, from then on, is not pure fact? "

"Furthermore, Geoffrey was the only source to hail the existence of King Tenvantius of Britain, until modern archaeologists began finding Iron Age coins bearing his name: "Tasciovantus". What other gems of the Archdeacon's history have been dismissed by today's historians?"