One magnificent specimen of Byzantine architecture, more within the reach of ordinary travellers, and consequently better known than San Vitale or Santa Sophia, must not be omitted, and can be studied easily by means of numberless photographic illustrations--St. Mark's at Venice. This cathedral was built between the years 977-1071, and, it is said, according to a design obtained from Constantinople. It has since been altered in external appearance by the erection of bulbous domical roofs over its domes, and by additions of florid Gothic character; but, disregarding these, we have alike in plan, structure, and ornament, a Byzantine church of the first class. [Illustration: FIG. 162.--PLAN OF ST. MARK'S AT VENICE.] The ground-plan of St. Mark's (Fig. 162) presents a Greek cross, _i.e._ one in which all the arms are equal, and it is roofed by five principal domes, one at the crossing and one over each of the four limbs of the cross. Aisles at a low level, and covered by a series of small flat domes, in lieu of vaulting, fill up the angles between the arms of the cross, so as to make the outline of the plan nearly square. The rich colouring of St. Mark's, due to a profuse employment of mosaics and of the most costly marbles, and the splendid effects produced by the mode of introducing light, which is admitted much as at Santa Sophia, are perhaps its greatest charm; but there is beauty in every aspect of its interior which has furnished a fit theme for the pen of the most eloquent writer on art and architecture of the present or perhaps of any day.