IV. In 1179 the cathedral was greatly damaged by fire. Either because of this, or because the eastern half of the cathedral had been planned so inconveniently, or because the plan was not the fashionable one of Norman times, the monks set to work to rebuild the whole cathedral. As usual, they arranged their building operations so as to avoid interfering with the services in the choir as long as possible. First, they rebuilt the north aisle of the choir, but not so high as it is at present. The aisle remained narrow, because Gundulph’s tower was in the way. But the south aisle of the choir they doubled in width. Next, they set to work at the east end, planning it, as at Hereford, as an eastern transept with an eastern aisle, and projecting eastward an oblong sanctuary (cf. Southwell). The new transept was lofty and broad; and it is quite possible that it was built over the top of Gundulph’s east end without disturbing daily services within it. Then, when all was finished, Gundulph’s east end was pulled down. Unlike the Worcester monks they preserved the level of the eleventh-century choir, and consequently had to continue Gundulph’s crypt eastward. In the new presbytery is seen the same curious mixture of quadripartite and sexpartite vaulting as in St. Hugh’s eastern transept at Lincoln. All this work was finished in 1227. Next they pulled down Gundulph’s narrow north transept and rebuilt it as broad as the central aisle of the nave. The new transept has a sexpartite vault with a longitudinal ridge rib, as in the great transept of Lincoln (_c._ 1245). Then came the rebuilding of the south transept (_c._ 1280). They resolved also to have a central tower and to rebuild the nave. Of the nave they rebuilt the two easternmost bays, and then completed the piers and arches of the crossing; but not yet the tower.