The great window in the central compartment is one of the finest examples of Geometrical tracery, if not one of the largest windows, in England. It is over 50 feet high, is 25 feet wide, and has seven lights. Of these the three at either end are comprised under a sub-arch, in the head of which are three cinquefoiled circles, while the central light of the seven is surmounted by an arch, not so high as its neighbours, but impaling upon its acute point a huge circle which fills the head of the window and contains six trefoils radiating from its centre. The arch of this superb window is rather acutely pointed and richly moulded, and has two very slender shafts worked on the stones of either jamb, with foliage on their capitals. Just above the ground below this window there may be observed in the wall one of the many architectural puzzles in which the Cathedral abounds, a half-arch, rising toward the right and filled in with masonry, except at the right side, where is a narrow opening that runs in for a few feet.[53] A string-course continued from the sides of the aisles passes below the three windows and round the buttresses, which are further relieved at a little height above it by a set-off. The gable has been entirely rebuilt by Sir Gilbert Scott. It is slightly set back, and displays a lofty window of four lights with geometrical tracery not unlike that in the great window below. On either side of this window there is panelling graduated to suit the triangular space, and the gable is crowned by an elaborate cross and flanked by two pinnacles which resemble those of the flying buttresses but are larger and have foliage at the corners instead of heads. The original Decorated gable was probably very much of this pattern. Its height was indicated by the weathering on the tower, and it seems to have had flanking pinnacles and graduated panelling. It had, however, been lowered in pitch and had been altered also by the insertion of a rather debased Perpendicular window.[54] Whatever may be thought, therefore, of Sir Gilbert Scott's action in rebuilding it, he has surely improved the general effect of the front, and it is well that one of the roofs, at any rate, should have been raised to the original pitch. What is most to be regretted, perhaps, is the removal of all traces, if any there were, of the chantry of the Holy Trinity _supra summum altare_, which was situated, as its name implies, in the roof, behind the old gable. In Archbishop Roger's day the choir was probably as long as it is now, and Walbran (followed by Sir Gilbert Scott) believed that the aisles at that period were returned across the east end. If so, the clearstorey must have been a bay shorter than at present, with a pent roof projecting from below it on the east side to cover the returned portion of the aisle. The rebuilding of the east end in the Decorated period was the first operation in which limestone was employed, but much of the old gritstone has been used again.