Byzantine Architecture, a mixed style, i.e. a style composed of Graeco-Roman and Oriental elements which, in earlier centuries, cannot be clearly separated. The form of church used most in the west, a nave supported on columns and an atrium (see Basilica), appears in many examples of the fifth century in Byzantium as well as in Rome; the sixth century saw such churches erected in other regions outside of Rome, at Ravenna, in Istria and in Africa. In the West this style of building occasionally presents (in S. Lorenzo and S. Agnese at Rome) peculiarities which are ascribed by some authorities to Oriental origin—galleries over the side aisles, spirally channelled columns, and imposts between capitals and arches. Vaulted basilicas are td be found at an early date in Asia Minor, Syria, Africa, and also at Constantinople. But the early Etruscans and Romans were skillful in the art of constructing vaults, even before that time; for instance, the basilica of Constantine: The domical style, with barrel-vaulted side aisles and transepts is a’ favorite with the Orientals; many of the oldest basilicas of Asia Minor, as well as the Church of St. Irene, Constantinople (eighth century), carried, one or more domes. This type leads naturally to the structure in a centralized—circular, octagonal, cruciform—plan. That the Orient had, and still has, a peculiar preference for such a type is well known; nevertheless, Italy also possessed ecclesiastical buildings so planned, of which the oldest examples belong to the fourth and fifth centuries (Sta. Costanza, a circular building; and the baptistery of the Lateran, an octagonal building). In ancient Roman times tombs and baths had this sort of plan. The essential type of all these buildings cannot, therefore, be regarded as purely Oriental, or even specifically Byzantine. There are similar objections in the case of subordinate architectural details. Thus the apse, sometimes three-sided, sometimes polygonal, the narthex (a narrow antechamber, or vestibule), instead of the large rectangular atrium, the invariable facing of the church to the east, the sharp-cut acanthus leaf of the capitals, and similar characteristics of the Eastern churches cannot be definitely ascribed to the East alone or even to Byzantium, nor do they form a new architectural style. Some authorities, it is true, not only go so far as to characterize the architecture of Ravenna (exemplified in the two churches S. Apollinare and S. Vitale) as Byzantine, but even include, without further consideration, examples which in other respects recall the favorite Eastern style., viz. the central portions of S. Lorenzo at Milan and of the round church of S. Stefano Rotondo at Rome. Only this much is certain: that in those early centuries local diversities are found everywhere; and that, even although Italy may have received the most manifold influences from the East, and particularly from Byzantium, still, on the other hand, the language, laws, and customs of Rome prevailed in Byzantium, or at least were strongly represented there.
In the church, now the mosque, of St. Sophia (Hagia Sophia— “Divine Wisdom”), built by Justinian, all the principal forms of the early Christian churches are represented. A rotunda is enclosed in a square, and covered with a dome which is supported in the direction of the long axis of the building by half-domes over semicircular apses. In this manner a basilica, 236 feet long and 98 feet wide, and provided with domes, is developed out of a great central chamber. This basilica is still more extended by the addition of smaller apses penetrating the larger apses: Then the domical church is developed to the form of a long rectangle by means of two side aisles, which, however, are deprived of their significance by the intrusion of massive piers, In front of all this, on the entrance side, are placed a wide atrium with colonnaded passages and two vestibules (the exonarthex is practically obliterated). The stupendous main dome, which is hemispherical on the interior, flatter, or saucer-shaped, on the exterior, and pierced with forty large windows over the cornice at its spring, has its lateral thrust taken up by these half domes and, north and south, by arched buttresses; the vertical thrust is received by four piers 75 feet high. The ancient system of column and entablature has here only a subordinate significance, supporting the galleries which open upon the nave. Light flows in through the numerous windows of the upper and lower stories and of the domes. But above all, the dome, with its great span carried on piers, arches, and pendentives, constitutes one of the greatest achievements of architecture. (These pendentives are the triangular surfaces by means of which a circular dome can be supported on the summits of four arches arranged on a square plan.) In other respects the baptistery of Sta. Costanza at Rome, for example, with its cylindrical drum under the dome, has the advantage that the windows are placed in the drum instead of the dome.
The architects of St. Sophia were Asiatics: Anthemius of Tralles and Isodorus of Miletus. In other great basilicas, as here, local influences had great power in determining the character of the architecture, e.g. the churches of the Nativity, of the Holy Sepulchre, and of the Ascension, built in Palestine after the time of Constantine. This is still more evident in the costly decorations of these churches. The Oriental love of splendor is shown in the piling up of domes and still more in facing the walls with slabs of marble, in mosaics (either opus sectile, small pieces, or opus Alexandrinum, large slabs cut in suitable shapes), in gold and color decorations, and in the many-colored marbles of the columns and other architectural details. Nothing, however, seems to betray the essentially Oriental character of Byzantine architecture so much as the absence of work in the higher forms of sculpture, and the transformation of high into low decoration by means of interwoven traceries, in which the chiselled ornaments became flatter, more linear, and lacelike. Besides the vestibules which originally surrounded St. Sophia, the columns with their capitals ‘recall the antique. These columns almost invariably supported arches instead of the architrave and were, for that reason, reenforced by a block of stone (impost block) placed on the top and shaped to conform to the arch, as may frequently be seen at Ravenna. Gradually, however, the capital itself was cut to the broader form of a truncated square pyramid, as in St. Sophia. The capital’s are at times quite bare, when they serve at the same time as imposts or intermediate supporting blocks, at other times they are marked with monograms or covered with a network of carving, the latter transforming them into basketlike capitals. Flat ornamentations of flowers and animals are also found, or leaves arbitrarily arranged. Much of this reminds one of the Romanesque style, but the details are done more carefully. The fortress-like character of the church buildings, the sharp expression of the constructive forms, the squatty appearance of the domes, the bare grouping of many parts instead of their organic connection—these are all more in accordance with the coarser work of the later period than with the elegance of the Greek. Two other types of Justinian’s time are presented by the renovated church of the Apostles and the church of Sts. Sergius and Bacchus. Both churches are in the capital. The latter somewhat resembles S. Vitale in Ravenna. It is a dome-crowned “octagon with an exterior aisle. The former church (now destroyed) was built on the plan of a Greek Cross (with four equal arms) with a dome over the crossing and one over each arm.
During the period of the Macedonian emperors, Basil I (867-886) and Leo VI (886-912), an upward trend in politics, literature, and art set in. The Greek basilica, which is a lengthened structure, barrel-vaulted and provided with one or more domes, is also widely represented in this period, while the western form of basilica, with the wooden ceiling, is completely discarded. A type appearing more frequently is the domical church plan or the Greek-cross plan. The Koimesis, or Dormitio, in Nicaea (ninth century) has a clear basilica plan. This is also true of the church of the Holy Mother of God (Hagia Theotokos) at Constantinople, dating from the tenth century, and of the churches of Mt. Athos. The church at Skripu in Boeotia, of the same period, has indeed three naves each ending in an apse, but the dome crowns the middle of the building as in the Greek-cross type. The exteriors of these churches, which are usually rather small, are treated with greater care and are artistically elaborated with alternations of stone and brick, smaller domes over the vestibules, a decidedly richer system of domes, and the elevation of these domes by means of drums. The interiors are decorated most gorgeously. It seems that they could not do enough in this respect. This can still be seen in the church of St. Luke in Phocis, at Daphni, in the Nea Moni at Chio, and others. In this period the perfected art of the capital becomes the model for the empire as well as for regions beyond its borders: Syria, Armenia, Russia, Venice, Middle and Southern Italy, and Sicily. For the West, it is only necessary to mention the church of St. Mark at Venice (978-1096).
After its occupation by the Crusaders (1204)-, Constantinople partly lost its character and at the same time the far-reaching influence of its intercourse with Western nations. There still remained four centers of Byzantine art: the capital itself, Mt. Athos, Hellas, and Trebizond. The architecture of Mt. Athos presents the most faithful reflection of the Byzantine style. The model’ of the church of the monastery of Laura, belonging to the previous period, is more or less faithfully reproduced. A dome, supported on four sides by barrel vaults, stands directly over the middle of the transept, which is terminated at either end by a round apse. A narthex, or rather two lead into the lengthened main hall. The real architectural ornaments are forced into the back-ground by the frescoes which take the place of the costly mosaics and which practically cover all available wall surface. The architecture of this period remained stationary. It continued unchanged in the countries of the Greek Rite after the fall of Constantinople (1453).