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) Cissa was reported as the viceroy of king Centwine of Wessex (reigned c.676-686). Cissa is sometimes said to have himself been a king of Wessex, but does not feature in the king lists or genealogies. He is said to have constructed Chisbury Camp, and to have founded Abingdon Abbey.
Ambicatus Ambicatus (or Ambigatos in Gaulish) is mentioned in the founding legend of Mediolanum (Milan) by Livy, whose source is Timagenes, as a king of the Bituriges, "kings of the world" as their name suggests, who ruled over the Celts in central Gaul, between Hispania and Germany, in the days of Tarquinius Priscus (the sixth century BCE). Ambicatus sent his sister's sons, Bellovesus and Segovesus, with many followers drawn from numerous tribes, to found new colonies in the Hercynian forest and in northern Italy, in the early sixth century BC. Bellovesus founded Mediolanum. If Ambicatus was an authentic historical figure, rather than a construct to express the linked origins of Celtic tribes in northern Italy and beyond the Alps, most likely he was the leader of the most powerful tribe in a military alliance, from which the Celtic colonizers of Italy were apparently drawn.