Examples of isolated towers are hardly to be found of later date than the thirteenth century. Bordeaux perhaps offers an exception. But the general usage after this period was to include the towers in the composition of the façade; their actual functions as belfries became apparent only above the level of the vaults. A beautiful example of this treatment may be studied in the noble composition of Notre Dame de Paris. Its contemporary, the Cathedral of Laon, has four towers, terminating in octagonal belfries, the angles of which are flanked by two-storied openwork pinnacles; on the second of these stories are placed colossal bulls, the effect of which is very striking. The towers of Rheims, which date from the second half of the thirteenth century, are of secondary importance in the splendid façade; but they are marked by a feature which was a novelty at the time. The interior of the belfry is built with a cage to allow free play to the bells, and space for the timbers by which they are supported, while the exterior forms an octagonal tower flanked by important pinnacles. Rheims may be said to mark in Gothic architecture the boundary which separated its period of perfection from that of exaggeration and mannerism. The mania for lightness and the desire to dazzle and astound soon seduced its artists into a dangerous path which led inevitably to decadence. Such effects first manifested themselves more especially in the provinces of the German frontier, and the spire of Strasburg, built in the fourteenth century, is a famous example of these mistaken tendencies. Throughout the fourteenth and fifteenth centuries towers adhered to the plan and general arrangement adopted by the later architects of the thirteenth century, diverging chiefly in the marvellous profusion of detail and of sculpture, and in the excessive lightness of design. The points of support were attenuated, and the mass of ornament seemed designed to conceal them as far as possible. In France the misfortunes of the times tended largely to perpetuate these dangerous foibles; for a number of churches which were founded at the close of the thirteenth century remained unfinished till the fifteenth and sixteenth, when Gothic art was in full decadence. [Illustration: 90. CHURCH OF ST. PIERRE AT CAEN. TOWER]