CONSTANTINE THE GREAT, who by establishing the Christian religion had encouraged the erection of basilicas for Christian worship in Rome and Italy, effected a great political change, and one destined to exert a marked influence upon Christian architecture, when he removed the seat of empire from Rome to Byzantium, and called the new capital Constantinople, after his own name. Byzantium had been an ancient place, but was almost in ruins when Constantine, probably attracted by the unrivalled advantages of its site, rebuilt it, or at least re-established it as a city. The solemn inauguration of Constantinople as the new capital took place A.D. 330; and when, under Theodosius, the empire was divided, this city became the capital of the East.
With a new point of departure among a people largely  of Greek race, we might expect that a new development of the church from some other type than the basilica might be likely to show itself. This, in fact, is what occurred; for while the most ancient churches of Rome all present, as we have seen, an almost slavish copy of an existing type of building, and do not attempt the use of vaulted roofs, in Byzantium buildings of most original design sprang up, founded, it is true, on Roman originals, but by no means exact copies of them. In the erection of these churches the most difficult problems of construction were successfully encountered and solved. What may have been the course which architecture ran during the two centuries between the refounding of Byzantium and the building of Santa Sophia under Justinian, we can, however, only infer from its outcome. It is doubtful if any church older than the sixth century now remains in Constantinople; but it is certain that, to attain the power of designing and erecting so great a work as Santa Sophia, the architects of Constantinople must have continued and largely modified the Roman practice of building vaults and domes. There is every probability that if some of the early churches in Byzantium were domed structures others may have been vaulted basilicas; the more so as the very ancient churches in Syria, which owed their origin to Byzantium rather than to Rome, are most of them of the basilica type.
A church which had been erected by Constantine, dedicated to Santa Sophia (holy wisdom), was burnt early in the reign of Justinian (A.D. 527 to 565); and in rebuilding it his architects, Anthemios of Thralles, and Isidoros of Miletus, succeeded in erecting one of the most famous buildings of the world, and one which is the typical and central embodiment of a distinct and very strongly marked  well-defined style. The basis of this style may be said to be the adoption of the dome, in preference to the vault or the timber roof, as the covering of the space enclosed within the walls; with the result that the general disposition of the plan is circular or square, rather than oblong, and that the structure recalls the Pantheon more than the great Hall of the Thermæ of Diocletian, or the Basilica of St. Paul. In Santa Sophia one vast flattish dome dominates the central space. This dome is circular in plan, and the space over which it is placed is a square, the sides of which are occupied by four massive semicircular arches of 100 ft. span each, springing from four vast piers, one at each of the four corners. The four triangular spaces between the corners of the square so enclosed and the circle or ring resting upon it are filled by what are termed “pendentives”—features which may, perhaps, be best described as portions of a dome, each just sufficient to fit into one corner of the square, and the four uniting at their upper margin to form a ring. From this ring springs the main dome. It rises to a height of 46 ft., and is 107 ft. in clear diameter. East and west of the main dome are two half-domes, each springing from a wall apsidal (i.e. semicircular) in plan. Smaller apses again, domed over at a lower level, are introduced, and vaulted aisles two stories in height occupy the sides of the space within the outer walls till the outline of the building is brought to very nearly an exact square. Externally this church is uninteresting, but its interior is of surpassing beauty, and can be better described in the eloquent language of Gilbert Scott than in any other: “Simple as  is the primary ideal, the actual effect is one of great intricacy, and of continuous gradation of parts, from the small arcades up to the stupendous dome, which hangs with little apparent support like a vast bubble over the centre, or as Procopius, who witnessed its erection, described it, ‘as if suspended by a chain from heaven.’
“The dome is lighted by forty small windows, which pierce it immediately above the cornice which crowns its pendentives, and which, by subdividing its lower part into narrow piers, increases the feeling of its being supported by its own buoyancy.
“The interior thus generated, covered almost wholly by domes, or portions of them, each rising in succession higher and higher towards the floating hemisphere in the centre, and so arranged that one shall open out the view to others, and that nearly the entire system of vaulting may be viewed at a single glance, appears to me to be in some respects the noblest which has ever been designed, as it was certainly the most daring which, up to that time at least, if not absolutely, had ever been constructed.” After pointing out how the smaller arcades and apsidal projections, and the vistas obtained through the various arched openings, introduced intricate effects of perspective and constant changes of aspect, Scott continues: “This union of the more palpable with the more mysterious, of the vast unbroken expanse with the intricately broken perspective, must, as it appears to me, and as I judge from representations, produce an impression more astounding than that of almost any other building: but when we consider the whole as clothed with the richest beauties of surface,—its piers encrusted with inlaid marbles of every hue, its arcades of marble gorgeously carved, its domes and vaultings resplendent with gold mosaic interspersed  with solemn figures, and its wide-spreading floors rich with marble tesselation, over which the buoyant dome floats self-supported, and seems to sail over you as you move,—I cannot conceive of anything more astonishing, more solemn, and more magnificent.”
The type of church of which this magnificent cathedral was the great example has continued in Eastern Christendom to the present day, and has undergone surprisingly little variation. A certain distinctive character in the foliage (Fig. 163) employed in capitals and other decorative carving, and mosaics of splendid colour but somewhat gaunt and archaic design, though often solemn and dignified, were typical of the work of Justinian’s day, and could long afterwards be recognised in Eastern Christian churches.
Between Rome and Constantinople, and well situated for receiving influence from both those cities, stood Ravenna, and here a series of buildings, all more or less Byzantine, were erected. The most interesting of these is the church of San Vitale (Figs. 160, 161). This building is octagonal in plan, and thus belongs to the series of round and polygonal churches and baptisteries for which the circular buildings of the Romans furnished a model; but in its high central dome, lighted by windows placed high up, its many subsidiary arcades and apses, the latter roofed by half-domes, and its vaulted aisles in two stories, it recalls Santa Sophia; and its sculpture, carving, and mosaic decorations are hardly less famous and no less characteristic.
One magnificent specimen of Byzantine architecture, more within the reach of ordinary travellers, and consequently better known than San Vitale or Santa Sophia, must not be omitted, and can be studied easily by means of numberless photographic illustrations—St. Mark’s at  Venice. This cathedral was built between the years 977-1071, and, it is said, according to a design obtained from Constantinople. It has since been altered in external appearance by the erection of bulbous domical roofs over its domes, and by additions of florid Gothic character; but, disregarding these, we have alike in plan, structure, and ornament, a Byzantine church of the first class.
The ground-plan of St. Mark’s (Fig. 162) presents a Greek cross, i.e. one in which all the arms are equal, and it is roofed by five principal domes, one at the crossing and one over each of the four limbs of the cross. Aisles at a low level, and covered by a series of small flat domes, in lieu of vaulting, fill up the angles between the arms of the cross, so as to make the outline of the plan nearly square.
 The rich colouring of St. Mark’s, due to a profuse employment of mosaics and of the most costly marbles, and the splendid effects produced by the mode of introducing light, which is admitted much as at Santa Sophia, are perhaps its greatest charm; but there is beauty in every aspect of its interior which has furnished a fit theme for the pen of the most eloquent writer on art and architecture of the present or perhaps of any day.
From Venice the influence of Byzantine art spread to a small extent in North Italy; in that city herself as well as in neighbouring towns, such as Padua, buildings and fragments of buildings exhibiting the characteristics of the style can be found. Remarkable traces of the influence of Byzantium as a centre, believed to be due to intercourse with Venice, can also be found in France. Direct communication with Constantinople by way of the Mediterranean has also introduced Byzantine taste into Sicily. One famous French church, St. Front in Périgueux, is identical (or nearly so) with St. Mark’s in its plan; but all its constructive arches being pointed (Fig. 3, page 5), its general appearance differs a good deal from that of Eastern churches—a difference which is accentuated by the absence of the mosaics and other coloured ornaments which enrich the walls of St. Mark’s. Many very old domed churches and much sculpture of the Byzantine type are moreover to be found in Central and Southern France—Anjou, Aquitaine, and Auvergne. These are, however, isolated examples of the style having taken root in spite of adverse circumstances; it is in those parts of Europe where the Greek Church prevails, or did prevail, that Byzantine architecture chiefly flourishes. In Greece and Asia Minor many ancient churches of Byzantine structure remain, while in Russia churches are built to the  present day corresponding to the general type of those which have just been described.
In ancient buildings of Syria the influence of both the Roman and the Byzantine models can be traced. No more characteristic specimens of Byzantine foliage can be desired than some to be found in Palestine, as for  example the Golden Gate at Jerusalem, which we illustrate (Fig. 163); but in the deserted cities of Central Syria a group of exceptional and most interesting buildings, both secular and sacred, exists, which, as described by De Vogüé,  seem to display a free and very original treatment based upon Roman more than Byzantine ideas. We illustrate the exterior of one of these, the church at Turmanin (Fig. 164). This is a building divided into a nave and aisles and with a vestibule. Two low towers flank the central gable, and it will be noticed that openings of depressed proportion, mostly semicircular headed, and with the arches usually springing from square piers, mark the building; while the use made of columns strongly resembles the manner in which in later times they were introduced by the Gothic architects.
 I.e. the City of Constantine.
 “The edge of the world: the knot which links together East and West; the centre in which all extremes combine,” was the not overcharged description given of Constantinople by one of her own bishops.
 ‘Lectures on Mediæval Architecture.’
 ‘Syrie Centrale.’