In all probability there was, according to the usual plan of Norman churches, a tower at the junction of the nave and transepts, and beyond this an apsidal choir. But there is no documentary record of such a tower ever having been built or fallen, although its existence is rendered probable by a carving of a church with tower and spire on Draper's chantry, and by a similar representation on a seal, and in two other parts of the building. It is probable that the original choir extended westward beyond the transept, as at Westminster to the present day. As has been stated above, the Norman church was commenced by Flambard towards the end of the eleventh century; and of the work so begun, the earliest existing remains are the arcading of the nave, the triforium, and the transepts with the eastern apsidal chapel attached to the south transept. Next to this in order came the walls of the aisles of the nave, and the cloisters and chapter-house, which, however, have disappeared; cloisters would come to be considered a necessity as soon as the secular canons were superseded by regulars. The early English clerestory of the nave seems to have been built in the time of the third prior, Peter, about the beginning of the thirteenth century. To the end of same century may be approximately assigned the vaulting of the nave aisles, the north porch, and a chapel attached to the north transept. Alterations of an extensive nature seem to have been begun in the fourteenth century; for to this date belong the rood screen, placed farther to the east than the old division between the ritual choir of the canons and the western part of the nave, which was probably given up to the lay dwellers in the parish,--and the splendid reredos. The Lady Chapel also was completed certainly before 1406, probably eleven years earlier. The fifteenth century saw the western tower built and the choir commenced and a great part of it finished, though the vaulting seems not to have been completed until the early part of the sixteenth century, as W. E. the initials of William Eyre, who was prior from 1502 to 1520, are to be seen on the bosses and the arch of the south choir aisle. Somewhat later still is the chantry at the east end of the south choir aisle, built by the last prior and dated 1529, and the chantry built by the last of the Plantagenets, Margaret, Countess of Salisbury, daughter of the Earl of Clarence and mother of Cardinal Pole, who at the age of seventy was executed by Henry VIII. in 1541.