pointed arched opening above the level of the springing of the vaults, and although larger than such openings had been in Romanesque design, it nevertheless is simply an opening in a wall, the area of the solid still 
FIG. 46. bis.being greater than that of the void. Beneath the clerestory is a circular opening, filled with a peculiar and beautiful form of tracery, occupying the space between the vaults of the triforium gallery and the timber roof which covers them. The whole design is one that exhibits a good deal of massive wall space, and an eye not quick to recognise leading structural features might not readily perceive that this is really a building whose stability resides not in its walls, but in its framework.
Early in the thirteenth century the original vaults of this nave, which had been completed in the preceding century, were damaged by fire and had to be repaired. [1] It would appear, indeed, that their lateral cells were wholly reconstructed and somewhat changed in form; for the longitudinal arches of the original cells which remain in place fall considerably below the present vault surfaces, [2] as may be seen in Fig. 46. Contemporaneously with this repairing and remodelling of these nave vaults great changes were making in other parts of the building—chiefly in the clerestory—in conformity with developments that had elsewhere taken place. These developments consisted chiefly in the enlargement of apertures, and in the dividing of them by mullions and simple forms of tracery. The apertures of the
- ↑ Viollet-le-Duc, s.v. Cathédrale, p. 292.
- ↑ They do so in some, though not in all, of the bays. Indeed, great and very puzzling variations are exhibited in the different bays of this clerestory. For instance, in the first five bays on the north side of the nave, counting from the choir, the original longitudinal ribs are surmounted by other arches, in each of which the extrados is more acutely pointed than the intrados, which follows the form of the old arch, thus giving a more pointed form to the vault cell than it had originally. But the sixth, seventh, and eighth bays have their old arches raised by stilting to the new level, and thus these cells have the same form that they had originally. In the sixth and seventh bays the outline of the window head is not concentric with the archivolt, but is rendered more pointed by a singular filling-in, as shown in Fig. 46 bis.
