Because of its resemblance to such ribbed domes as those just described it may be well to discuss here what may be called a “Gothic dome” if such a term be permissible. This is, in other words, the familiar chevet vault extended to cover a space of circular or octagonal plan. One of these vaults of circular plan and with eight ribs appears over the crossing of Saint Nicolas at Blois (Fig. 56). Unlike the ribbed dome, its masonry courses are not horizontal and concentric with the impost line, but practically at right angles to it, thus giving wall arches whose crowns are nearly as high as the central keystone itself. Each window cell is thus precisely like one-quarter of a four-part cross-ribbed vault. It was this form of double chevet vault which was frequently used as late as the Renaissance period in Italy, where it appears in such works as the Pazzi chapel at Florence (cir. 1420) (Fig. 57) and elsewhere though without [Illustration: FIG. 56.--BLOIS, SAINT NICHOLAS.] [Illustration: FIG. 57.--FLORENCE, PAZZI CHAPEL.] [Illustration: FIG. 58.--WORMS, CATHEDRAL.] any wall rib. These “Gothic domes” were frequently polygonal as well as circular. Thus in the cathedral of Worms (Fig. 58) there is an octagonal lantern, on squinches, surmounted by a vault with eight cells of decidedly domical type, the whole being only slightly different from a lobed dome. A more developed double chevet, dating from the second half of the fifteenth century, appears over the crossing of the cathedral of Evreux (Eure),[324] where there is also a complete system of ribs.[325] The form of the pendentives is that of flat triangles, and they are decorated with elaborate designs in flamboyant tracery. Similar flat triangles but with a series of mouldings at the top, are used to support the octagonal lantern of Coutances cathedral (Fig. 59), perhaps the most beautiful in France, and apparently dating from the second half of the thirteenth century. Its vault is in sixteen cells, two to each lantern wall, and each containing a lofty window, the whole clerestory rising above a lower stage of coupled arches with a narrow passage behind them. [Illustration: FIG. 59.--COUTANCES, CATHEDRAL.] A crossing vault of similar character, but with a change in the arrangement of the ribs, which form an eight-pointed star around a central octagonal opening, is to be seen in the cathedral of Saragossa in Spain (after 1500),[326] while the final stage in such vaulting, in which the ribs become merely a framework beneath a flat ceiling, but nevertheless a framework of elaborate and beautiful design, may be seen over the crossing of the cathedral of Burgos (finished 1568).[327] SQUARE LANTERNS WITH EIGHT-PART VAULTS