The two lateral arches under the dome are filled by clearstory walls pierced by twelve windows, and resting on arcades in two stories carried by magnificent columns taken from ancient ruins. These separate the nave from the side-aisles, which are in two stories forming galleries, and are vaulted with a remarkable variety of groined vaults. All the masses are disposed with studied reference to the resistance required by the many and complex thrusts exerted by the dome and other vaults. That the earthquakes of one thousand three hundred and fifty years have not destroyed the church is the best evidence of the sufficiency of these precautions. Not less remarkable than the noble planning and construction of this church was the treatment of scale and decoration in its interior design. It was as conspicuously the masterpiece of Byzantine architecture as the Parthenon was of the classic Greek. With little external beauty, it is internally one of the most perfectly composed and beautifully decorated halls of worship ever erected. Instead of the simplicity of the Pantheon it displays the complexity of an organism of admirably related parts. The division of the interior height into two stories below the spring of the four arches, reduces the component parts of the design to moderate dimensions, so that the scale of the whole is more easily grasped and its vast size emphasized by the contrast. The walls are incrusted with precious marbles up to the spring of the vaulting; the capitals, spandrils, and soffits are richly and minutely carved with incised ornament, and all the vaults covered with splendid mosaics. Dimmed by the lapse of centuries and disfigured by the vandalism of the Moslems, this noble interior, by the harmony of its coloring and its impressive grandeur, is one of the masterpieces of all time (Fig. 77). +LATER CHURCHES.+ After the sixth century no monuments were built at all rivalling in scale the creations of the former period. The later churches were, with few exceptions, relatively small and trivial. Neither the plan nor the general aspect of Hagia Sophia seems to have been imitated in these later works. The crown of dome-windows was replaced by a cylindrical drum under the dome, which was usually of insignificant size. The exterior was treated more decoratively than before, by means of bands and incrustations of colored marble, or alternations of stone and brick; and internally mosaic continued to be executed with great skill and of great beauty until the tenth century, when the art rapidly declined. These later churches, of which a number were spared by the Turks, are, therefore, generally pleasing and elegant rather than striking or imposing. [Illustration: FIG. 78.--PLAN OF ST. MARK’S, VENICE.] [Illustration: FIG. 79.--INTERIOR OF ST. MARK’S.]