There is a lot of change to political boundaries in Britain in the The Arthurian Age. This page shows a variety of maps showing what we know, but more often our bests guesses. Below you will find sections devoted to time periods relevant to the Arthurian Age, which is roughly the fifth century, with some overlap into the fourth and sixth centuries. Feel free to contact me with questions, comments, etc. It will take some time to complete this page.
“Celtic” Britain prior to Roman Invasion of 43 AD
The British Isles were inhabited by Celtic speaking people who identified with their tribes and did not see themselves as “British”, “Irish”, “Picts”, or “Celts”. The tribes of Ireland spoke a different Celtic language than those of Britain. The Picts spoke a language that was very similar to the Britons, and the Celtic language of the Britons seems to have been very similar to that of the Celts of Gaul (France).
Roman Britain by 390 AD
Britain about 410 AD