What was the empire of King Arthur called?

King Arthur is a legendary character, there is little evidence that he ever existed - despite this the Welsh Annals and Welsh Triads are a useful source of information. The legends suggest that if he did exist he was an British king (British in this case referring to the pre-Saxon dwellers of the land). Mythology refers to his castle being Camelot, but this is almost certainly a name given much later. If indeed Camelot did exist Cadbury Castle in Somerset is considered by some to be the most likely site of Arthur's base as excavations in the 60's and 70's showed re-fortification during the 5th/6th century and that it was used as a base by a powerful leader and his men.