"Old Cornwall" included Devon, Arthurian Cornwall would have consisted of present-day Devon and Cornwall, and the sunken land of Lyonesse [Liones] to the west, of which the Scilly Islands are the touted remains.

Subkingdoms include Lyonesse, the South Marches, and Tintagil.

Chrétien tells us that Arthur regularly reinforced his army with men drawn from Cornwall.