l82 COMPARATIVE ARCHITECTURE. for the pouring out of libations, or sacrifices to their gods, was now used for the celebration of Christian rites, and a haldachino, or canopy, supported on marble columns, was erected over it. In later times the altar was frequently placed against the east wall of the apse (No. 72). The interiors of these buildings owe their rich effect to the use of glass mosaic ("opus Grecanicum,") which was placed fre- quently in a broad band (No. 74) above the nave arcading and to the semi-dome of the apse (No. 78 g, k), which is frequently richly treated with a central figure of Christ seated in glory and set in relief against a golden background. " Below was all mosaic choicely planned, With cycles of the human tale."' The ceilings of timber were also formed in compartments and were richly gilded (Nos. 74 and 76). The pavements were formed out of the abundant store of old columns and other marbles existing in Rome, slices of columns being used as centres surrounded by bands of geometric inlay twisted with intricate designs (No. 78 B, l). The old Basilican Church of S. Peter (a.d. 330) was erected near the site of the martyrdom of S. Peter in the circus of Nero. It had a " transept," or " bema," 55 feet wide, and 113 feet high (No. 75 a, b, c). Five arches, the centre called the arch of triumph, gave access from the body of the church, and at the sanctuary end was a semicircular apse on a raised floor, against the centre of the wall of which was the Pope's seat. The priest stood behind the altar, and thus faced east, as the chancel was at the west end of the church. S. John Lateran (a.d. 330) has been altered so much in modern times as to have lost its early character. There were in all thirty-one Basilican churches in Rome, mostly made up of fragments of earlier pagan buildings. The interiors of these basilicas are impressive and severe, the repetition of the long rows of columns being grand in the extreme, as in the interior view of S. Paolo fuori le mura (Nos. 74, 75 e), built A.D. 3S0 by Theodosius but re-erected in a.d. 1821, and S. Maria Maggiore (Nos. 75 d and 76). There are also important examples at Ravenna, a city well situated for receiving the influence of Constantinople, and at one time the seat of an Exarch of the Empire. S. Apollinare Nuovo, a.d. 493-525, built by Theodoric the Goth, and S. Apollinare in Classe, a.d. 538-549, are important three- aisled Basilican churches carried out by Byzantine artists on Roman models, and they are interesting for the impost blocks to the capitals supporting the pier arches, and the fine mosaics. At Torcello, near Venice, the foundations of the original
