BYZANTINE ARCHITECTURE The decline of Roman imperialism was automatically accom panied by that of Roman architecture and its influence. To govern the empire from a more central location, Constantine, in A.D. 324, moved his capital from Rome to Byzantium, an ancient Greek city, to be known thenceforth as Constantinople. The same emperor had already established Christianity as the State religion, and when Byzantium was rebuilt on Roman lines the new form of worship made itself felt architecturally. As the power of Rome decreased, that of Christianity, which was destined to be come the new unifying world force on which later civilizations would be built and later architecture developed, grew steadily.
Byzantine is the term applied to the style of architecture evolved in the new capital of the Roman empire. Constantine erected many churches, law courts and other buildings, practically all of which contained columns and slabs taken bodily from Roman buildings. These structures were neither indigenous to the country nor of durable form, and little or nothing of them remains. The architecture of the period had scant significance until Rome's influence diminished and what was built became more expressive of the new country, the new government and the new faith.
Passing to Justinian's time (A.D. 527-565) we find St. Sophia built between A.D. 532 and A.D. 537. It marks the highest develop ment of the Byzantine style. In it the arch and vault, which, as explained in the section on Western Asia, probably originated in the East, were extensively developed. Christianity appealed to the mass of the population and required buildings that could accommodate congregations; it was devoted to one God instead of many; consequently it produced large churches rather than num erous small temples for various deities as earlier religions had.
St. Sophia affords one of the most perfect examples of high development of vault and dome. The great central space was acquired by means of the vast central dome which rests on pendentives (q.v.) leading down to four massive piers. The lat eral thrust is cared for by secondary and much lower arches equally reinforced; the longitudinal thrust by two half domes each divided again into three semi-domes. The architects, An themius of Tralles and Isodorus of Miletus showed extraordinary skill in solving their problem. It is doubtful if modern engineers would attempt to reproduce such construction without employing the principle of the steel skeleton. In fact, the dome fell in A.D. 555, and when rebuilt it was raised higher and pierced round its lower part with 4o circular-headed windows, which give an effect of extraordinary lightness to the structure. When considered in terms of its great span and comparatively great height, the main dome is a mere shell of unbelievable thinness.
The structure is of brick, and its being built of small elements bound together by a strong lime cement—an art developed highly by the Romans—explains the seeming mystery of its stability.
The binding nature of the cement actually absorbs the tensile strains to which it is subjected. The building measures 26oft. from entrance door to eastern apse ; in width, including the aisles, 23 8f t. ; and I 7 5 f t. from floor to the apex of the central dome. The Roman idea of surface decoration is carried to extremes; the Greek idea of structural expression in architecture disappears totally. The walls and vault above were covered with mosaics on a gold ground. The columns of the whole church on the ground floor are of porphyry, and on the upper storey of verd antique. The columns and arches give scale to the small apses, the small apses to the larger ones, and the latter to the dome, so that its immense size is grasped from the first. The lighting is admirably distributed, and the rich decoration of the marble slabs, the mono lith columns, the elaborate carving of the capitals, the beautiful marble inlays of the spandrils above the arches, and the glimpses here and there of some of the mosaic showing through the stucco, all give a magnificent effect to the interior. Although often de based into a purely decorative feature, the column was used with real structural significance throughout the Roman work, in which it retained sufficient size to be an impressive element in the com position. But in St. Sophia the structural importance of the col umn is small, and in contrast with the enormous dome, Io7ft. in diameter, it is a secondary factor, more decorative than otherwise.
The exterior of St. Sophia has little of architectural interest except its size. Here again is a marked change from the Roman point of view, which made the superficial appearance of a building the most important element in its composition. To impress the passing throng must have been as important to Roman builders as the ceremonies carried on within their buildings. At the advent of Christianity the congregation and the ceremonies within an enclosed space became the means of impressing people. Byzan tine architecture, which gave such predominant importance to the interior, has had its influence on subsequent buildings up to the present day. Its best examples, however, have appeared in south-eastern Europe. In the course of time the exteriors of buildings were embellished also, the most notable example of such treatment being St. Mark, Venice. (See also BYZANTINE and