The term Byzantine has been given to the style of architecture which was the outcome of the fusion of the best building traditions of the East and of the West, the former contributing the distinctive structural feature of the dome, with the minor details of richness of colouring and lavishness of decoration, the latter dignified symmetry of proportion and scientific solidity of construction.
It was in Byzantium, when in 330 the first Christian Emperor chose it as his headquarters, and its name was changed in his honour to Constantinople, that the union which was to be so prolific of results took place. Unfortunately however none of the churches erected under the auspices of Constantine in the new capital have been preserved, the sole relic of his reign, so far as architecture is concerned, being the foundations of the apse of a church, now replaced by a considerably later building, in which he had the Holy Sepulchre at Jerusalem enclosed. The oldest existing church in Constantinople is a basilica of the Roman type dating from 463, with nothing distinctive of the new style about it, but there is historical evidence that the noble S. Sophia, in which that style reached its fullest development, was preceded in Constantinople by other grand buildings of a similar type, including one dedicated to the Holy Apostles which was cruciform in plan and had five domes.
The most distinctive peculiarity of Byzantine architecture is the roofing over of square spaces with the aid of the pendentive, a clever expedient already explained, that was carried to great perfection by the builders of Constantinople and those who elsewhere followed their example. Previously employed in comparatively small structures, it now became the fundamental principle for the roofing over of spaces of a great variety of extent, groups of domes and semi-domes, in many cases supplemented by tapering towers rising with imposing effect from massive outer walls. The long aisles and nave of the Roman and early Christian basilicas were replaced by a more or less square plan, lofty piers spanned by arches upholding the central cupola, whilst the galleries above the aisles rested on slender columns such as were also employed to rail off the sanctuary and narthex from the main body of the building. The whole of the interior, which was lighted from windows in the dome, was most profusely decorated, the walls having dados or slabs of different coloured marbles supplemented by mosaics, with which every portion of the domes, semi-domes, and pendentives were also covered, whilst the columns, in many cases of variegated marble, had beautifully carved capitals of an infinite variety of design.
It is customary to divide the history of the development of Byzantine architecture into two distinct periods, the first extending from the 4th to the close of the 6th century, the second from the 8th to the 13th century, there having been a pause between them during which no buildings of any importance were erected owing to the wars which convulsed alike the East and the West. As already stated, no actual buildings belonging to the earlier portion of the first period remain, but there exist in S. Vitale at Ravenna and still more in S. Sophia at Constantinople unique examples of the golden age of Byzantine architecture, the inspiring influence of which was felt throughout the whole of Europe and the greater part of Asia. The former church, begun about 526, is of octagonal plan, each division, except that containing the choir, with an apse of its own, and though the interior has been greatly spoiled by restoration, the general effect of the vaulted roofing, marble casing of the walls, and mosaics of the eastern end is extremely fine. San Vitale is, however, altogether excelled by the world-famous S. Sophia, now the chief mosque of Constantinople, which occupies the site of a basilica built under Constantine, that was burnt down early in the reign of Justinian. The latter emperor at once ordered the erection of its successor, appointing as architects Anthemios of Thralles and Isodoros of Miletus.
Begun in 532 and completed in 537, S. Sophia is of very simple yet most dignified external appearance, so symmetrical is the grouping of its many domes and semi-domes, whilst the interior, though it has none of the rich colouring usual in oriental buildings, is unsurpassed in the harmony of its structural details, all of which lead up, as it were, to the huge central dome, the lower portion of which is pierced with a series of small windows throwing a flood of light upon the vast circular space below. The general plan is square, but a fine narthex consisting of two spacious halls one above the other projects slightly beyond the actual church at the western end. The nave, which is 106 feet wide by 225 long, has a semicircular apse with small recesses opening out of it at either end, and is separated from the aisles by rows of closely set columns with ornate capitals, spanned by arches upholding two-storied arcaded galleries, roofed in by semi-domes, except at the northern and southern ends, which have walls with numerous small windows. One large western window illuminates the nave, and there is also a double circle of lights round the apse, the galleries, and the narthex.
Other interesting early Byzantine buildings are the Baptistery at Kalat-Seman and the church of S. George at Ezra, both in Syria, each of which is of square plan with an octagonal central space, the latter having the comparatively unusual feature of a dome upheld by what is known as a drum, that is to say a low vertical wall instead of pendentives. The church of S. Sergius at Constantinople, contemporaneous with S. Sophia, is specially noteworthy on account of the introduction in it of a classic entablature, combined with distinctive Byzantine features, with which may be named the much-restored S. Lorenzo at Milan and the church of the Virgin at Misitra, the ancient Sparta.
To the second period of Byzantine Architecture belong not only several fine buildings in Constantinople, but others in Greece, Asia Minor, the North of Italy, and elsewhere, all of which, though they have the leading structural features of the style, are distinguished by certain minor local characteristics. The most noteworthy in the capital are the now secularised church of S. Irene, founded by Constantine and rebuilt considerably later, and the church of the Chora monastery, specially remarkable for its beautiful mosaics, whilst in Greece the Churches of S. Nicodemus at Athens and that of Daphni not far from it, with the two monastic churches at Stiris and the churches of S. Sophia and S. Elias, at Salonika, are all thoroughly Byzantine, bearing a close resemblance to each other. They are all, however, excelled by the great Cathedral of S. Marco at Venice, which rivals even S. Sophia in the exquisite beauty of the interior and excels it in the ornate richness of the exterior.
Founded early in the 9th century, S. Marco was partially destroyed in 978 and rebuilt soon afterwards in the original style, that of a basilica without transepts, but in the second half of the 11th century it was completely transformed by additions converting it into a cruciform building, roofed over by five domes of the same size, and with five arcaded porches at the western end that form one of the grandest façades in the world. Numerous columns of many covered marbles uphold graceful arches, the spandrels, or triangular spaces between them filled in with gleaming mosaics, and above them rise other arches that contrast well with tapering towers supported on slender pilasters to which the domes beyond form an admirable background. Within the church to which this magnificent narthex gives entrance, an infinite variety of harmonious details combine to produce an entrancing effect: one charming vista succeeding another, the whole flooded with light from a vast number of windows, there being no less than eighty in the domes alone. Mosaics of different dates and greatly varying æsthetic merit completely clothe the surfaces of the vaulting, the capitals of the columns—many of which, by the way, are purely decorative, upholding no arches—are elaborately carved, and the flooring is of marble, slabs of considerable size being set in patterns of tesseræ.
In the various countries which fell under the influence of the followers of Mahommed a style of architecture was evolved that had marked affinities with the Byzantine, the first mosques having been designed, it is supposed, by Christian architects of Oriental origin, who retained the square or circular ground-plan of early churches, though they modified the interior to suit the requirements of the new religion, introducing, for instance, a central tank for ablutions. Mosques intended for worship only, generally had flat roofs, the use of the dome being at first distinctive of a burial place, but as it very soon became usual to inter in mosques, the dome came to be quoted as a distinctive feature of them. By degrees simple unadorned mosques were replaced by vast buildings with many arcaded courts entered from ornate lateral doorways, whilst certain characteristic features were introduced, of which the chief were the stalactite vaulting, the name of which explains itself, the horse-shoe arch, and the minaret, the last named a turret of several stories gradually decreasing in circumference, each with a balcony of its own from which the mueddin calls the faithful to prayer. Pointed arches were also constantly employed as well as the form known as cusped, that is to say one with a triangular projection springing from the inner curve. A minor but most significant characteristic of Saracenic architecture is the elaborate surface decoration in which geometrical designs, letters, &c., are interwoven with consummate skill, but in which no figures of animals are ever introduced, the representation of life being strictly forbidden by the Koran.