The Church of St. Ouen at Rouen, except for the west front and its towers, which are modern, is a typical example of the rare religious buildings constructed in the north of France during the fourteenth century. The arrangement of these churches varies, inasmuch as, while in general they follow the methods of construction adopted by the Northern architects of the thirteenth century, their special characteristic is a refinement or rather an attenuation of the piers, less by actual reduction of their section than by a diminution of their apparent bulk. This was effected by multiplying the clustered shafts, the slenderness of which was still further exaggerated by the prodigality of the mouldings, and the over-hollowness of their profiles. These profiles and mouldings rise from the base to the summit, and in the fourteenth century mark the spring of the arches by rings of sculpture, crowned with rudimentary abaci. These latter details were the last traces of a tradition which was to finally disappear in the fifteenth century. Thenceforward the lines of the intersecting arches of the vault, as of the longitudinal and transverse arches, run down without interruption to the base of the piers, where we find a complex faggot of mouldings crossing and recrossing, and showing little beyond the technical dexterity of the carver. The main preoccupation of the architects of this period seems to have been the reduction of solid surfaces so as to give full play to the soaring effect of their airy shafts and vaults. The walls disappear, save below the windows, which now occupy the entire space of each bay. The triangular divisions of the vault are concealed by a serried network of supplementary ribs, for the most part useless save as decorations. But it must in justice be remembered that to this exaggeration of the window spaces we owe the growth of the beautiful art of painting on glass. This art, the admirable fitness of which for decorative purposes can hardly be over-estimated, had already manifested itself in the twelfth and thirteenth centuries. In the interval from that period to the Renascence it produced its grandest masterpieces.[19] [19] See chap. xii. "Decorative Painting on Walls and Glass."