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 the 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 Rome, at Ravenna, in Istria, and in Africa. In the West this style of building occasionally presents (in S. Lorenzo and S. Agnes 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 to be found at an early date in Asia Minor, Syria, Africa and also at Constantinople. But the early Etruscans and Romans were skilful 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 favourite with the Orientals; many of the oldest basilicas in 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 favourite 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