As long as we all remember that the history of this period is 99% guesswork from very limited and contradicory sources, we'll all have a lot of fun. It's when people start connecting it with who invented jigs and reels, or who has a right where and how to live in 2002, that it gets a bit heated. I love the many and varied fanciful reasons people have come up with for Gildas never mentioning Arthur. I like the theory that Arthur was actually one of the Old People who tried to keep the Celts out, and was subsequently absorbed into Celtic mytholgy as one of their heroes, and subsequently again by the English. We all need heroes! I would recommend "Facing the Ocean: the Atlantic and its peoples" by Barry Cunliffe for an overview of the last 10,000 years. He carefully avoids any serious discussion of Arthur. Quite a dry historical tome really, but very sound on the North Channel shortbread trade in 500AD.