208 COMPARATIVE ARCHITECTURE. large mosaic decorations, hence it is now known as the "mosaic mosque." It is supposed by some that the facade of this church served as a model for that of S. Mark, 'enice (No. 85). The Church of the Holy Apostles, Constantinople, founded by Constantine the Great, but rebuilt by Justinian, and destroyed in a.d. 1463, to make way for the Mosque of Sultan Mahomet II., was the second type of Byzantine plan, and is interesting as being the prototype of S. Mark, Venice (Nos. 84, 85, 86) (see below). S. Vitale, Ravenna (a.d. 526-547) (No. 83 c, d), whose prototype was the Temple of Minerva Medica at Rome (No. 83 A, b), is octagonal on plan, an inner octagon of 50 feet being inclosed by an outer one of no feet. The apsidal chancel opens from the inner octagon, by a square bay cutting through the outer aisle. The relation of the chancel to the octagon is successfully designed. It is to be noted that the other seven arches of the inner octagon have columns placed on a half circle, carrying round the gallery usual in Eastern churches. In many particulars Byzan- tine influences are seen. The dome is composed of earthen pots, and protected by a wooden roof, thus difTering in construction from Roman examples. The church built by Charlemagne, and containing his tomb, at Aix-la-Chapelle (No. 83 e, f), is derived from this church (see page 261). S. Mark, Venice (Nos. 84, 85 and 86), was erected, for the most part, between ad. 1063-1071, the columns and marble mosaics to the exterior being added between 1 100-1350. Venice was by situation one of the connecting links between the Byzantine and Franconian Empires, and a great depot of the traffic between the East and West, which is evident in Venetian architecture. The plan of S. Mark (No. 84 c) is in the form of a Greek cross, of equal arms, covered by a dome in the centre (42 feet in diameter), and one over each arm of the cross, and is derived from the Church of the Holy Apostles at Constantinople. It is worthy of note that the square piers, which carry the dome, are pierced on the ground floor and gallery levels : the gallery arcade connects the piers on either side, the depth of the gallery being that of the pier. The vestibules fill out the western arm of the cross to a scjuare on plan. The interior (Nos. 84 a and 86) is richly veneered with colored marbles casing the lower part of the walls ; above, and extending in one great surface over vault and dome, is a lining of richly colored glass mosaic, in which are worked figures of saints mingled with scenes from their lives, set off by a broad background of gold. Mosaic, in fact, is the real and essential decoration of the church, to which all architectural detail is subordinated.
