 The historic Bishop of Dorchester was a prelate who administered the Diocese of Dorchester in the Anglo-Saxon period.The bishop's seat, or cathedra, was at the cathedral in Dorchester-on-Thames in Oxfordshire.In the 660s the seat at Dorchester-on-Thames was abandoned, but briefly in the late 670s it was once more a bishop's seat under Ætla, under Mercian control.