 Following his injury in a fall from the scaffolding in 1179 he was replaced by one of his former assistants, known as "William the Englishman".In 1180–4, in place of the old, square-ended, eastern chapel, the present Trinity Chapel was constructed, a broad extension with an ambulatory, designed to house the shrine of St Thomas Becket.A further chapel, circular in plan, was added beyond that, which housed further relics of Becket, widely believed to have included the top of his skull, struck off in the course of his assassination.