Gildas’ letter was recopied and spread throughout Britain. Initially it was so popular because he had the gall to attack British kings (that was his main point actually), but it had staying power because Gildas’ was the only version of British history for the first century after Rome left. Let’s take a moment to dwell on that, a bishop with an axe to grind against British kings, who manipulated and invented history to follow his themes, was renowned as the great British historian. Hmm. O.K. I’m over it.
In 597, Kent welcomed an envoy of Christian leaders and the king allowed himself to be baptized. Overnight, Kent became a kingdom capable of recording history. More importantly, Kent was the only Germanic kingdom capable of recording history and therefore the only kingdom capable of creating a history that no one else could deny. This was probably the moment when the Kentish Source was created. This history had one objective, to demonstrate that Kent was the most legitimate kingdom in Britain.
Kent only had one written history to contend with, Gildas. But in that was the key to their early history. Gildas had said that one man had united Britain, and a king of the entire island was the only person who could legitimize the Germanic people being there. Gildas said that the British king had been manipulated by the Germanic leaders, which made the Germanic leaders his natural successors. What was missing were names. We know from our historical sources that an Ansehis was a foederati leader who came to Britain during the fourth century. Ansehis/Anschis is linguistically similar to Hengest. If he was still remembered as a great early leader in the seventh century, it would have been natural for Kent to claim him as their ancestor. He worked even better as the man who had manipulated Vortigern.
It was this history that Bede was given when he set to work on his Historia Ecclesiastica in 729. Bede was uncertain of whether or not to trust the source (and his wording makes that clear) but he used it because he didn’t have another option. Even his native Northumbria had no early traditions. That’s a shame, too, because there is a passage in Historia Brittonum (829) that suggests Deira might have been the first independent Germanic kingdom.