The cathedral was badly damaged during Danish raids on Canterbury in 1011. The Archbishop, Alphege, was taken hostage by the raiders and eventually killed at Greenwich on 19 April 1012, the first of Canterbury's five martyred archbishops. After this a western apse was added as an oratory of St. Mary, probably during the archbishopric of Lyfing (1013–1020) or Aethelnoth (1020–1038).
The 1993 excavations revealed that the new western apse was polygonal, and flanked by hexagonal towers, forming a westwork. It housed the archbishop's throne, with the altar of St Mary just to the east. At about the same time that the westwork was built, the arcade walls were strengthened and towers added to the eastern corners of the church