Hi Joe,
You are too quick to dismiss Gildas as a source of serious history. He is obviously completely ignorant of the history of the various Roman provinces in Britain - however, as an historical source for how quickly this ignorance decended following the abandonment of Britain it's invaluable - Gildas was born within a century of the collapse of the Empire and was extremely well educated.
His historical value lies in the fifty year period from his birth (concurrent with the Seige of Badon) and the writing of the Excido. Critically the contemporary references to British tyrants - even if politically biased (which they are) - must have an element of truth as his readers will have known, or known of, these men. The description of Ambrosius Aurelianus' campaign is significant because it was written within living memory of the events it describes.
It was not written as history but to dismiss the Excido as a source isn't supportable.
Pete
God is our guide! from field, from wave, From plough, from anvil, and from loom; We come, our country's rights to save, And speak a tyrant faction's doom: We raise the watch-word liberty; We will, we will,we will be free!