At some time, but we do not know exactly when, the Church or Chapel of St. Andrew adjoining the north nave aisle of the monks' church, extending as far east as the sixth bay, was built for the use of the parishioners, who had no right to enter the monastic church. This Church of St. Andrew opened into the north aisle of the Abbey Church, being separated from it by an arcade of four arches. It had a nave with aisle and chancel. Its total length was about 140 feet, its width about 61 feet. It is conjectured that the north-western tower was converted into a kind of antechapel or entrance porch for the Church of St. Andrew. There was a door leading from the aisle of the Abbey Church into the chancel of St. Andrew's; this door, walled up, may still be seen in the fifth bay from the west end. In order to avoid the necessity of returning again to the history of this church, it may here be stated that it was rebuilt by John Wheathampstead after he had been re-elected to the office of Abbot in 1451; and that it was destroyed after the dissolution of the monastery, when there was no longer any need for it, as the parishioners bought the Abbey Church for parochial use. The place of the old arcading was then taken by a blank wall without any windows; this was pulled down and the present wall built by Lord Grimthorpe. In the latter half of the thirteenth century the reconstruction of the eastern end was begun by Abbot John of Hertford. Here, as in many other churches, the Norman choir was too short for thirteenth-century requirements. The walls of the presbytery were raised and its high-pitched roof converted into a flat one. The church was gradually extended eastward by Abbots Roger of Norton and John of Berkhampstead; first the Saint's Chapel was built, then the retro-choir, and finally the Lady Chapel, which was finished by Abbot Hugh of Eversden in 1326.