 The west front has two 13th century <unk> towers 27 @.@ 4 metres ( 90 ft ) high that were originally topped with wooden <unk> covered in protective lead . Although the difference between the construction of the base course and the transepts suggests that the towers were not part of the initial design , it is likely that the building process was not so far advanced that the masons could fully integrate the nave and towers into each other ( Fig . 7 ) . 
