Sec. 44. There is one obvious consequence of the setting out of aisles on either side of an existing building which, although an imperfection in itself, contributes greatly to the variety of the parish church plan. The builders cannot see both their aisles at one and the same time: the older church comes in between. In fact, until the nave and aisles are actually joined, at the close of the work, by the breaking down of the walls beneath the arches, there can be no opportunity of appreciating the full effect of the work. There is a famous instance at Beverley minster of the mistakes to which the presence of the older building may lead. The aisles of the nave were set out in the fourteenth century on either side of an older and shorter nave. The south aisle was set out first, the width of the eastern bay being measured from a new buttress in the angle of nave and transept. On the north side there was a thirteenth century buttress in this position: the builders, in setting out their north aisle, overlooked the fact that this buttress was of less projection than the newly built one on the other side, with the result that their buttress measurements throughout varied on both sides, while the standard of width between the buttresses, which had been employed on the south side, was retained. Consequently, as the columns, in a vaulted church, have to be built in line with the buttresses of the corresponding aisle walls, the columns were not opposite one another, and the discrepancy increased as the church advanced westward. When the builders got clear of the intervening building, in the western bays of the nave, they were able to rectify their mistake slightly; but the effect is unpleasantly noticeable in the obliquity of the transverse arches of the vaulting.