Page:Charles Moore--Development and Character of Gothic Architecture.djvu/96

Rh Without this concentration of thrusts, as far up as they extend, that compactness of the pier, which is so essential to the Gothic system, could not exist. How this form of the clerestory was afterwards taken advantage of for larger openings we shall see when we come to consider modes of enclosure. For the present we must confine our attention to the forms and adjustments of the vaults, the vaulting supports, and the general framework of the buildings of the early thirteenth century in France. Meantime, however, it may be remarked that the ribs of the vaults of these, as of the earlier buildings, consist only of such as have a constructive office—namely, the transverse, the diagonal, and the longitudinal ribs. Ridge ribs and surface ribs, which sometimes appear later, do not occur at this epoch. Of the constructive ribs none are ever wanting, nor are independent supports for them ever wanting in the piers. Throughout the building there is a structural reason for every member that meets the eye, though the degree of perfection with which minor structural exigencies are met continues to vary.

In the nave of St. Leu d'Esserent, whose vaults we have just considered, the lower piers and the vaulting shafts are wrought substantially on the model of those of the westernmost pier of Paris; but they differ in having a complete capital over the engaged column which sustains the vaulting shafts, as well as in having the central portion of the great abacus in the form of a square set diagonally to the axis of the nave, instead of a circle, and also in having the longitudinal rib shaft rest upon the clerestory ledge instead of resting upon the same capital which carries the diagonal rib. This nave is one of the very earliest of the constructions of the thirteenth century, and its design, in many points, resembles rather the work of the latter part of the twelfth century—to which epoch it might be supposed to belong were it not for the forms of the lower piers, the character of its capitals, and the forms of the clerestory openings which shall be noticed farther on.

The nave of the Cathedral of Chartres followed quickly after that of St. Leu, which it closely resembles in main features, though the design is carried out on a much grander scale. Here the vaults, which in St. Leu are constructed