202 COMPARATIVE ARCHITECTURE. The two semi-domes, east and west, abut against the great arches which support the central dome and act as buttresses to it on the east and west sides. The smaller exedrx^ are also covered with semi-domes, as has been stated. The pendentives carrying the central dome have a projection of 25 feet and a height of over 60 feet. The great piers supporting the dome are of stones, the rest of the building being of brickwork. The construction of the dome is explained on No. 80. Internally, the actual effect of the whole is one of extreme intricacy, although the general scheme is very simple, while scale is obtained by the careful gradation of the various parts from the two-storied arcades to the aisles and lofty dome, which rests, with little apparent support, like a canopy over the centre, or, as Procopius, an eye-witness, described it, " as if suspended by a chain from heaven." The impression is that of one great central domed space with semicircular domed ends, the height gradually decreasing from 179 feet at the centre. The walls and piers are lined with beautifully-colored marbles (Phrygian white, Laconian green, Lybian blue, Celtic black, white marble with black veins from the Bosphorus, and Thessalian marble), in varied patterns, fixed by means of metal cramps ; the floors are laid with colored mosaics of various patterns, and the vaults and domes are enriched with glass mosaics of the apostles, angels, and saints on a glittering golden ground. Although many of these are now concealed by matting covered with plaster, or are replaced by quotations from the Koran, yet the four pendentives still exhibit the six-winged seraphim, whom Mahometans acknow- ledge under the names of the four Archangels, Gabriel, Michael, Raphael, and Israfil, and when the light is favourable the figure of Christ can still be seen in the vaults of the apse. The columns of many-colored marbles are used constructively to support the galleries which rest on a variety of groined vaults. Moulded bronze rings encircle the column shafts at their junction with the capitals and bases, and elsewhere. The lower stories of the aisles (north and south of the central space) are supported by four columns of dark green marble from the Temple of Artemis (Diana) at Ephesus, the upper stories having six columns of the same material. Each of the four small exedrae has two large columns of dark red porphyry below, brought from the Temple of the Sun at Baalbec, and six smaller columns on the upper story. The total number of columns in the church is 107 (the same number as the diameter of the church in feet), of which forty are below and sixty-seven above. The capitals are mostly of the pyramidal or cubiform type, Vf'ith small Ionic angle volutes and delicately incised carving.
