 The first church was markedly cruciform in shape and smaller than the present floor plan . This early structure had a choir without aisles and more truncated , and a nave with only a single aisle on its north and south sides ( Fig . 4 ) . The central tower rose above the crossing between the north and south transepts and may have held bells in its upper storey . The north wall of the choir is the earliest extant structure , dating to the years immediately after the church 's 1224 foundation ; the clerestory windows on top of it are from the later post @-@ 1270 reconstruction . This wall has blocked up windows extending to a low level above ground , indicating that it was an external wall and proving that the eastern limb then had no aisle ( Fig . 5 ) . 
