IV. GEOMETRICAL (1245-1315).—In this period the bell tower was carried up; and a magnificent Lady chapel was built (_c._ 1290), like that at Bristol, to the north of the choir, but detached from it. It could not be built east of the choir, as a high road passed close to the apse. This Lady chapel was pulled down in the seventeenth century for the sake of its materials. [Illustration: FROM SOUTH-EAST.] V. CURVILINEAR.—In this period the weight of the Norman tower, which had of course very thick walls, and was three or four stories high, was found to be too much for the exceptionally weak piers on which it stood. Warned, perhaps, by the fate of the central towers of Ely and Wells, both of which collapsed about this time, they took down the Norman tower, and built a new one (which has recently been rebuilt), much lighter and much lower. And they strengthened its eastern and western semicircular arches by inserting pointed arches beneath them. The south-west spire was also built—a design of exquisite beauty. VI. PERPENDICULAR.—The monks wanted to have a Galilee porch, and they inserted one between the piers of the west front, where it was constructionally useful by keeping the piers from bulging in. The wooden screens were now inserted in the central transept. Peterborough, after 1116, seems to have had a singular immunity from fire; so, very unlike Norwich, the monks did not take the slightest trouble to make their church fireproof. The whole of the high roofs are of wood. That of the nave may possibly be the original twelfth-century ceiling. A twelfth-century wooden roof still covers the Bishop’s Palace at Hereford. The choir has a wooden vault of the fifteenth century. VIII. In another respect the history of the church is uneventful. The eastern limb must have been exceedingly inconvenient, for there was no processional aisle or ambulatory round the apse. Every other large church pulled down or altered its eastern limb to suit the ritual: the Peterborough monks, always conservative and always behind the times, did not provide a processional aisle till the latter days of Gothic. And even then they took a very long time about it. The works seems to have been suspended in 1471, and not resumed till 1496. Even then, good conservatives that they were, they did not pull down the apse, but erected the New Building round it. It is a rich specimen of TUDOR work, with a fan vault. IX. In the matter, too, of the roof-drainage the Peterborough monks were slow to move. Instead of dripping eaves they constructed gutters and parapets to the aisles in the early years of the thirteenth century, and to the apse a little later. It was not till _c._ 1330 that they provided the high roofs of nave and choir with gutters and parapets; and, with their wonted conservatism, they retained the Norman corbel-table. [Illustration: RETRO-CHOIR]