After this time, and towards the end of the fifth century, we find the characteristic features of Christian art more insisted in: such as the colossal portraits and figures of Christ, the isolation of single figures, the symmetrical grouping of crowds of smaller figures, and of the representatives of the angel, bull, eagle, and lion, as winged symbols of the Evangelists, all rendered the more impressive by the architectural spacing, and the plain blue ground which surrounded most of the figures. Two churches may be mentioned that contained fine examples of the above type of early Christian mosaics; one is the great basilica of St. Paul, without the walls at Rome, built under Theodosius and Honorius about A.D. 386, and the other that of St. Cosmo e Damiano in Rome. The great mosaics in the apse of the latter church were executed between A.D. 526 and 530 by Pope Felix IV. The floors of these churches are made of what is known as “Opus Alexandrinum,” the finest and grandest floor decoration that exists (Fig. 334). Circular slabs of porphyry and serpentine marble sawn in disks from antique columns are laid down, and twisted interlacings and rings surround them as bands composed of triangular bits of white, black, or coloured marble, forming simple and effective patterns in a quiet harmony of colour. Some of this work may be seen in Westminster Abbey. [Illustration: Fig. 334.—Opus Alexandrinum Pavement, San Marco, Rome.] In the early part of the sixth century Christian art in Italy was at a low ebb, as by this time nearly all the antique remains and culture had been used up; but fortunately, the Eastern and Western Churches were not as yet divided in doctrine, and a fresh life had been imparted to Italian art from the Byzantine culture of the Eastern Empire. Besides the basilica form of building, another antique form of early Christian architecture was developed, called a “baptistery,” which generally took the form of a detached building, with a circular or polygonal plan. In some cases the baptistery adjoins the atrium of the basilica, but often is a detached building of considerable importance. The structure is supposed to have been suggested by the circular portion of the Roman baths, and consists of a circular row of columns supporting the upper structure; the central portion is surrounded by a low cloister-like aisle, and the fountain is in the middle of the building. The circular building known as the Church of Santa Costanza in Rome—the funeral chapel before mentioned—the octagonal baptistery of Constantine, and the fine baptistery at Ravenna, are examples of this kind of building. Another beautiful example is the octagonal baptistery of the Lateran, belonging to the fifth century; it has eight large antique columns, which support an architrave, upon which rest another series of eight smaller columns, carrying another architrave and the domed roof. The whole building has a pleasant and agreeable effect of extreme airiness.