BYZANTINE ARCHITECTURE. I95 80, 82, 83 B, 84, 86, III c) ; whereas in Roman architecture these features were as a rule placed over a circular apartment. Windows were now formed in the lower portion of the dome, which in the later period was hoisted upon a high circular drum, a feature which was still further embellished in the Renaissance Period by the employment of a circular peristyle or colonnade. In vaulting, porous stones, especially pumice, were used ; some- times the domes were constructed of pottery, as at S. Vitale, Ravenna (No. 83 d), where it is formed with urns and amphorae placed side by side and grouted with mortar. The architecture of the Byzantines was thus developed by the use of brick in the fullest manner, especially in domical vaulting, and there is an absence of preparatory and auxiliary work, M. Choisy remarking that the "greater number of their vaults rose into space without any kind of support " {i.e., without centering), by the use of large flat bricks, which is quite a distinct system, not derived from a Roman but from an Asiatic source. Byzantine art is the Greek spirit working on Asiatic lines, for the dome on pendentives was invented and perfected entirely in the East. In the Byzan- tine system of vaulting the vault surfaces gave the conditions of the problem, and the groins or angles of intersections were of secondary importance, presenting a direct contrast to the mediaeval buildings of Europe. The grouping of the smaller domes round the larger central one was very effective externally (No. 79), and one of the most remarkable peculiarities of Byzantine churches was that the tunnel vault and the dome had no additional outer covering, but were visible externally (No. 80 a); thus in no style does the elevation so closely correspond with the section as in the Byzantine. From the time when the architect permitted the forms of the vaults and arches to appear as architectural features in the faqades, the regular entablatures of the Romans were abandoned, and in the church of S. Sophia is seen the fully-developed Byzan- tine style : for whereas in the older buildings of Rome the columns and entablatures could be and were removed with- out causing the ruin of the building, in S. Sophia the true Greek expression of truth in construction was reverted to, its columns and capitals being not merely ornamental, but really supporting the galleries. The Classic orders were dispensed with, and the semicircular arches made to rest directly on columns designed for the purpose. The capitals, of which there are seven distinct types, four being in S. Sophia, assume a novel form (Nos. 88 and 89), appropriate to their new purpose of receiving the springers of arches, the voussoirs of which were always square, and not set in receding planes, as in so-called Gothic architecture. As Freeman says : " The problem was to bring the arch and column into union — in other words, to teach the column to o 2
