In my book THE ARTHUR OF HISTORY, I indicated that Arthur's father's name - Arthwys - may, in fact, be a territorial designation for the region of the Irthing River. [Arth = 'bear', while the -wys could be the suffix -wys, which is the Welsh form of Latin -enses.] We find both the Birdoswald Dark Age hall and the Camlann of Arthur along the Irthing. What follows is an article written by place-name expert Dr. Andrew Breeze, who believes that Irthing means "Little Bear".
Breeze, Andrew, Celts, bears, and the River Irthing, Archaeologia Aeliana, Society of Antiquaries Newcastle Upon Tyne, note 5, 34, 2005, 152-153: