Who was perhaps not the only king of the West Saxons at the time, whos viceroy is said to have constructed Chisbury Camp, and to have founded Abingdon Abbey?
Cissa (West Saxon):  He is said to have constructed Chisbury Camp, and to have founded Abingdon Abbey. Centwine of Wessex: Centwine (died after 685) was King of Wessex from c. 676 to 685 or 686, although he was perhaps not the only king of the West Saxons at the time.
Centwine