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The vaults commonly found are the barrel vault, the cross-groined vault, and the dome-vault. The first is frequently used over the cross arms and the bema, and sometimes over the narthex in conjunction with the groined vault (Diaconissa). It is the simplest method of covering an oblong space, but it does not easily admit of side windows above the springing.

A very beautiful form of cross-groined vault is found in S. Sophia and in SS. Sergius and Bacchus, in which the crown is considerably domed, and the groins, accordingly, lose themselves in the vaulting surface. This form is found in Greek churches of late date, but does not occur in the later churches of Constantinople. A full description of the form and construction is given by Choisy31 and by Lethaby and Swainson.32

The cross-groined vault as found in the Myrelaion and many other churches of the city is level in the crown, with clearly marked groins. It is sometimes used with transverse arches resting on pilasters, or without these adjuncts.

One of the most interesting of the vault forms is the dome-vault, a shallow dome with continuous pendentives. It is distinguished in appearance from the groined vault, as found in S. Sophia, by the absence of any groin line, and is completely different in construction.

The geometrical construction is that of the pendentives of all domes. The four supporting arches intersect a hemispherical surface whose diameter is equal to the diagonal of the supporting square. The pendentives produce at the crown line of the arches a circular plan which is filled in by a saucer dome of the same radius as the pendentives, constructed of circular brick rings, the joints of which radiate to the centre. If the space to be covered is not square the broader arches intersect at a higher level, while the narrow arches are not stilted, but kept down so as to receive the dome surface, and in this case the narrow arches are not semicircular, but segmental. Where the difference in size between the two sides was not great, the difficulty presented was easily overcome by the Byzantine builder, who in the later buildings, at any rate, rarely built anything within four inches of its geometrical position. Where the difference was too great it was frankly accepted, and we find segmental arches at the narrow ends.

The vaulting of the outer narthex of S. Saviour in the Chora illustrates this fully (Fig. 11). Though some of the bays of that narthex are oblong and others almost square all are covered with dome vaults. The almost square bays, although their sides vary considerably, are covered precisely as if their sides were exactly equal. But in two of the oblong bays, which are nearly three times as long as they are broad, such a method could not be applied. Longitudinal arches (AA) were accordingly thrown between the transverse arches (CC) and made to rest on their spandrils. The oblong form of the intervening space was thus very much reduced, and over it flat domes are thrown. Their rings are true circles, and as the space they cover is still somewhat oblong they descend lower, with additional segments of rings (BB), at the ends than at the sides. In the remaining two oblong bays of the narthex, the result of introducing the longitudinal arches is to convert a decidedly oblong space in one direction into a slightly oblong space in the opposite direction, an additional proof, if any were needed, that the exact shape of plan with this form of vault was a matter of comparative indifference to the builder.

In S. Sophia the vault springs from the intrados of the transverse arches, that is, from the lower edge. In SS. Sergius and Bacchus it springs from a point so slightly raised as to be hardly noticeable. In the later vaults, however, the transverse arches, when present, are boldly shown, and the vault springs from the extrados or outer edge (e.g. S. Saviour in the Chora, S. Theodore).

Construction.—Most of the churches of the city are covered with thick coats of plaster and whitewash, both within and without. Only in a few cases, where these coatings have fallen away through neglect, or in some remote corner of a building to which these coatings were never applied, can the construction and the laying of the brickwork be studied. The two-storied chapel, known as Bogdan Serai (p. 283), is almost denuded of plaster, and is therefore of importance in this connection. The bricks of the wall arches on which its dome rests are laid considerably flatter than the true radiating line, leaving a triangular piece to be filled in at the crown. On the other hand, the bricks of the transverse arches under the dome radiate to the centre.

It has been supposed that the method followed in the wall arches was employed in order to economise centering, since bricks could gradually be worked out over the space, each course simply sticking to the one below. This is undoubtedly the case in some examples. But here centering could not have been of any service in the wall arches, and the transverse arches are laid without flattening of the courses, though that arrangement might have been useful in their case. It is therefore more probable that the flattening of the courses in the wall arches is simply a piece of careless workmanship. The pendentives, like all pendentives that could be examined, were formed of horizontal courses corbelled out to the circle. The dome, bema, and the barrel vault in the lower story (p. 285) seem to be laid with true radiating joints. The springing of the barrel vault is formed of four courses of stone laid horizontally and cut to the circle, and above them the entire barrel is of brick. The dome arches of the Sanjakdar Mesjedi (p. 270) are formed of three distinct rings, not bonded into one another. They radiate to the true centre, and the pendentives are, as usual, in horizontal courses. The transverse arches of the outer narthex in S. Saviour in the Chora are also built with true radiating courses.

The gynecaeum of the side-chapel of the Pammakaristos (p. 153) has never been plastered, and consequently the laying of the brickwork can be seen there to advantage. The little stair leading up to the gallery is covered with a sloping barrel vault built in segments perpendicular to the slope of the stair and could easily have been built without centering. The same remark applies to the cross vault at the head of the stair, which is similarly constructed in 'slices' parallel to each side (p. 154). The arches of the gynecaeum itself, the vaults, and the two little domes, seem to have true radiating joints. The ribs of the domes are formed in the brickwork, and are not structurally separate. In these last examples, and in all door and window openings, in which the joints invariably radiate from the centre, a certain amount of centering was inevitable.

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On the other hand a little passage in S. Saviour in the Chora between the church and the parecclesion (p. 311), is covered with a barrel vault evidently built without centering. The space is first narrowed by two corbelled courses of stone and, above them, by three projecting courses of brick. From this springs the vault, built from each end in strongly inclined segments. These segments meet in the middle, leaving a diamond-shaped space filled in with longitudinal courses. Like the stairs in the Pammakaristos, this passage is very narrow, some 85 cm., yet the builders thought it necessary to corbel out five courses before venturing to throw a vault without centering.

Near the Pantokrator is an octagonal building, now Suleiman Aga Mesjedi but generally regarded as a Byzantine library, which has on each side a large wall arch strongly elliptical in form (p. 270). Two arches of somewhat similar form and apparently original are found in the south end of the gynecaeum of the Pantokrator (p. 237). These arches may have been built in this manner to economise centering. Still, in the library they are wall arches easily constructed without centering.

Failing the examination of a larger number of buildings in Constantinople we can hardly judge of the later methods of vault and arch construction, but one point may be further noticed. The wall internally is often set back slightly at each spring course, so that with the projection of the course a considerable ledge or shelf is left. On this ledge centering could easily be supported and would have required no further framework to the ground. Centering seems to have been used for dorm, arches, vaults, and door and window openings. It was not used in small vaults. But it is difficult to imagine any method of constructing such groined vaults as those found in the narthexes of the Pantokrator without a very considerable amount of centering.

Ties.—As a general rule tie rods or beams were used, either of iron or wood. In the latter case they were painted with leaf or fret ornaments, and were evidently considered as natural features. But large vaults are often found without such ties as in the narthex of the Pantokrator. Many churches have ties to the dome-arches, and none to the main vault; but it is difficult to lay down a fixed rule. The enormous amount of mortar in the walls must have made them yield to a certain degree when newly built, and some of the larger vaults would have been the better for rods.

Abutments.—The system of abutments in the Byzantine churches of the great period has been carefully studied by M. Choisy. 33 In early examples the dome springs directly from the pendentives on the inside, but is thickened externally over the haunches, producing a double curve and an apparent drum. This is seen very clearly in SS. Sergius and Bacchus. In S. Sophia the numerous windows are cut through this drum, so that it resembles rather a series of small abutments. The object was to support the crown of the dome by adding weight over the haunches. In both these churches the thrust of the dome and its supporting arches is taken by the two-storied galleries, which form, in fact, flying buttresses within the buildings, and are adapted to their architectural requirements. The square plan and the enormous size of the dome in S. Sophia demanded the great buttresses on the sides; while in SS. Sergius and Bacchus the eight buttresses show only on the outside of the dome and are not carried over the aisles as they are in S. Sophia. Below the roof the arches and piers of the galleries and aisles are arranged so as to carry the thrust to the external walls, and following the tradition of Roman vaulting all buttressing is internal. In S. Irene, where the true drum dome first appears, the buttresses between the windows of the dome still remain, though much reduced in size. A dome raised on a drum can evidently no longer exercise a thrust against the dome-arches; its thrust must be taken by the drum, and only its weight can rest on the arches.

The weight of the drum and dome rests on the pendentives and dome-arches. Their thrust is neutralized by the use of ties and by the barrel vaults of the cross arms, and these in their turn depend on the thickness of the walls. The lower buildings attached to the church in the form of side-chapels and the narthex also helped to stiffen and buttress the cross walls. The system is by no means perfect in these late churches. It was apparently found impossible to construct drum domes of any size, except at the extreme risk of their falling in, and probably it is for this reason that many of the larger domes in late churches, like SS. Peter and Mark, S. Theodosia, the Chora, have fallen. No system of chainage appears to have been used for domes in Constantinople.

Flying buttresses probably of the ninth century are used at the west end of S. Sophia. The double-flying buttress to the apse of the Chora does not bond with the building and is certainly not original. It may be set down as part of the Byzantine restoration of the church in the fourteenth century. In any case, such external flying abutments are alien to the spirit of Byzantine architecture, and may be regarded as an importation from the West. Flying buttresses, it may here be noted, are not uncommon in the great mosques of the city. They are found in Sultan Bayazid, Rustem Pasha, Sultan Selim, the Suleimanieh, and the Shahzadé. But they are generally trifling in size, and are rather ornaments than serious attempts to buttress the dome.

Walls.—The walls of the earlier churches are built of large thin bricks laid with mortar joints at least as thick as the bricks, and often of greater thickness. Stone is used only in special cases, as in the main piers of S. Sophia, but monolithic marble columns are an important part of the structure. In the later churches stone is used in courses with the bricks to give a banded effect, and herring-bone, diamond, and radiating patterns are frequently introduced. The palace of the Porphyrogenitus, the parecclesion of the Pammakaristos, and Bogdan Serai, exhibit this style of work. As illustrations of the method adopted in the construction of walls the following measurements may be given, the sizes being in centimetres:

Building Procedure.—The first step in the erection of a building was to obtain the necessary marble columns with their capitals and bases. These seem to have been largely supplied ready made, and Constantinople was a great centre for the manufacture and export of stock architectural features. Then the main walls were built in brick, the columns were inserted as required, the vaults were thrown, and the whole building was left to settle down. Owing to the enormous amount of mortar used this settling must have been very considerable, and explains why hardly a plumb wall exists in Constantinople, and why so many vaults show a pronounced sinking in at the crown or have fallen in and have been rebuilt. After the walls had set the marble facings, mosaic, and colour were applied and could be easily adapted to the irregular lines of the walls.

Byzantine architecture made little use of mouldings. The great extension of flat and spacious decoration rendered unnecessary, or even objectionable, any strong line composition. External cornices are in coursed brick, the alternate courses being laid diagonally so as to form the characteristic dentil. The richest form is that found in the Pammakaristos, S. Theodosia, and S. Thekla, where the small dentil cornice is supported on long tapering corbels, a design suggested by military machicolations.

The stone ogee, cavetto, or cavetto and bead cornice is common, but seems in every case to be Turkish work and is very common in Turkish buildings. Internal cornices and string-courses are in marble, and are all of the same type, a splay and fillet. The splayed face is decorated with upright leaves or with a guilloche band, either carved (in the Pantepoptes) or painted (in the Chora), the carving as in classic work, serving only to emphasise the colour. The splay is sometimes slightly hollowed, sometimes, as in the Chora, worked to an ogee.

Doors.—Doors often have elaborately moulded architraves and cornice. In S. John of the Studion (p. 61), the oldest example, the jamb-moulding has a large half-round on the face, with small ogees and fillets, all on a somewhat massive scale. The doors of S. Sophia are very similar. The later mouldings are lighter but the half-round on the face remains a prominent feature. It is now undercut and reduced in size, and resembles the Gothic moulding known as the bowtell. This is combined with series of fillets, small ogees, and cavettos into jamb-moulds of considerable richness. The cornices are often simply splayed or are formed of a series of ogees, fillets, and cavettos. The jamb-mouldings are cut partly on a square and partly on a steep splayed line. In some, the portion forming the ingo seems to have been regarded as a separated piece though cut from the solid. If in the doors of the Pantokrator or the Pantepoptes the line of the inner jamb be continued through the rebate, it will correspond on the outside with the bowtell moulding, as though the inner and outer architrave had been cut from one square-edged block, placing the bowtell at the angle and adding the rebate. This formation is not followed in S. John of the Studion.

Carving.—Carving is slight, and is confined to capitals, string-courses, and the slabs which filled in the lower parts of screens and windows. Fragments of such slabs are found everywhere. They are carved with geometrical interlacing and floral patterns, often encircling a cross or sacred monogram, or with simply a large cross. Such slabs may be seen still in position in S. Sophia and in the narthex of S. Theodore. In the latter they are of verd antique, and are finely carved on both sides. In later times the embargo on figure sculpture was considerably relaxed. Little figures are introduced in the cornices of the eikon frames in the Diaconissa (p. 186), and both in the parecclesion and the outer narthex of the Chora are found many small busts of angels, saints, and warriors carved with great delicacy. The carving in the Chora is the finest work of the kind excepting that in S. Sophia.

Capitals.—The development of the capital from the Roman form, which was suitable only for the lintel, to the impost capital shaped to receive an arch has been well explained by Lethaby and Swainson. According to these authors Byzantine capitals exhibit seven types.

I. The Impost capital.—It is found in SS. Sergius and Bacchus, the outer narthex of the Chora, the inner narthex of S. Andrew and elsewhere. A modification of this type is used in windows. It was employed throughout the style but especially in early times up to the sixth century, and again in the twelfth, thirteenth, and fourteenth centuries.

II. The Melon type.—This is seen on the columns of the lower order in SS. Sergius and Bacchus and on the columns of the narthex of S. Theodore, where they have been taken from an older building. The melon capital was probably not in use after the sixth century.

III. The Bowl capital.—This type is used in the great order of S. Sophia at Constantinople. It has been thought peculiar to this church, but the capitals from S. Stephen at Triglia in Bithynia resemble those of S. Sophia closely. Only the peculiar volutes of the S. Sophia capitals are absent.34

IV. The Byzantine or 'Pseudo-Ionic.'—This is found in the upper order of SS. Sergius and Bacchus, and in the narthex of S. Andrew. It is an early type, not used after the sixth century, and its occurrence in S. Andrew favours the early date assigned to that church.

V. The Bird and Basket.—Found in Constantinople, only in S. Sophia.

VI. The Byzantine Corinthian.—This is the commonest form of capital in the later churches, and must have been in continuous use from the earliest date. It occurs in S. John of the Studion, the Diaconissa, the Chora, and in many other churches. Here the classic form is accurately adhered to, but, as the curved abacus was unsuitable to the arch, a large splayed abacus or impost block is placed above the capital. It is a general feature of the Byzantine capital that it projects at no point beyond the impost line of the arch, thus differing both from the classic and the Gothic forms.

VII. The Windblown Acanthus.—This is found in the churches of Salonica and Ravenna. Three examples are mentioned as seen in Constantinople, two near the Diaconissa, forming bases for the posts of a wooden porch to a house; one is the cistern commonly known as the cistern of Pulcheria.

Window Capitals.—In shafted window of several lights, the impost piers between the arches are of the full thickness of the wall, but are very narrow from side to side. Similarly the shafts are almost slabs placed across the wall, and sometimes, as in the Pammakaristos, are carved on their narrow faces. The capitals are cubical, of slight projection at the sides, but spreading widely at the ends, while the bases closely resemble capitals turned upside down. As with columns, the joints at base and necking are bedded in sheet lead.

Floors.—The floors are usually of thick red brick tiles, some .31 cm. square, or, as in S. Theodore, hexagonal, .34 cm. across by 45 cm. from point to point. Marble floors were used when possible, inlaid with patterns, or in slabs surrounded by borders of coloured marbles, as is still seen in a portion of the floor in the Pantokrator (Fig. 76).

Decoration.—Of the churches of Constantinople only S. Sophia, S. Mary Diaconissa, the South Church of the Pantokrator, and the Chora, retain any considerable part of their original decoration. The first is beyond our present scope, but from the general tone and atmosphere which still linger there we are able to appreciate the effect of the same style of decoration where it survives in less complete form.

The accepted method, as may be observed in the Chora and the Diaconissa, was to split marble slabs so as to form patterns in the veining, and then to place them upright on the wall. It is probable that the finest slabs were first placed in the centre points of the wall, and that other slabs or borders were then arranged round them. The centre slabs in the Chora are of exceptional beauty. The usual design consists of a dado of upright slabs surmounted by panelling to the cornice level, the panels being outlined with plain or carved beads. In the Diaconissa the notched dentil form is used for the beads; in the Chora, a 'bead and reel.' The arches have radiating voussoirs, or, in the Diaconissa, a zigzag embattled design, found also in S. Demetrius of Salonica, though two hundred years must have separated the buildings. In the Chora the arch spandrils and cornice are inlaid with scroll and geometrical designs in black, white, and coloured marbles.

The surfaces above the cornice and the interior of the domes gleamed with mosaic, representing, as seen in the Chora, figures on a gold background. The mosaic cubes are small, measuring 5 mm. to 7 mm., and are closely set. This is about the same size as the mosaic cubes in S. Sophia, but smaller than those at Ravenna, which measure about 10 mm.

Painting.—In the majority of churches this full decoration with marble and mosaic must have been rendered impossible by the expense, and accordingly we find examples like the parecclesion at the Chora decorated with painting, following exactly the tradition of marble and mosaic. This painting is in tempera on the plaster, and is executed with a free and bold touch.

Conclusion.—Byzantine architecture is essentially an art of spaces. 'Architectural' forms, as we are accustomed to think of them, are noticeably absent, but as compensation, colour was an essential and inseparable part of the architecture. The builder provided great uninterrupted spaces broken only by such lines and features as were structurally necessary—capitals, columns, string-courses, and over these spaces the artist spread a glittering robe of marble or mosaic. No school has ever expressed its structure more simply, or given fuller scope to the artist, whether architect or painter.

Byzantine architecture is not only a school of construction, it is also a school of painting. Most of the churches of Constantinople have unfortunately lost the latter part of their personality. They are mere ghosts, their skeletons wrapped in a shroud of whitewash. Still the Greek artist retained his skill to the last, and the decorative work of S. Saviour in the Chora will stand comparison even with the similar work in S. Sophia.

In Byzantine times the greatness of S. Sophia tended to crush competition. No other ecclesiastical building approached the 'Great Church.' But structural ability was only latent, and displayed its old power again in the erection of the imperial mosques of the early Turkish Sultans, for they too are monuments of Greek architectural genius.

The origins of Byzantine architecture have been discussed at great length by Strzygowski, Rivoira, and many other able writers. Much work still remains to be done in the investigation of the later Roman and early Byzantine work; nor does it seem probable that the difficult questions of the Eastern or the Western origin of Byzantine art will ever be finally settled.

The beginnings of Byzantine architecture have never been satisfactorily accounted for. With S. Sophia it springs almost at once into full glory; after S. Sophia comes the long decline. It may, however, be noted that the 'endings' of Roman architecture are similarly obscure. Such buildings as the Colosseum, in which the order is applied to an arched building, are evidently transitional, the Roman construction and the Greek decoration, though joined, not being merged into one perfect style. Even in the baths and other great buildings of Imperial Rome the decoration is still Greek in form and not yet fully adapted to the arched construction. At Spalatro, in such parts as the Porta Aurea, a developed style seems to be on the point of emerging, but it is not too much to say that in no great Roman building do we find a perfect and homogeneous style.

There is nothing in either the planning or the construction of S. Sophia which cannot be derived from the buildings of the Roman Imperial period, with the exception of the pendentive, a feature which had to be evolved before the dome could be used with freedom on any building plan on a square. The great brick-concrete vaulted construction is that of the Roman baths, and with this is united a system of decoration founded on the classic models, but showing no trace of the Greek beam tradition which had ruled in Rome.

S. Sophia then may be regarded as the culminating point of one great Roman-Byzantine school, of which the art of classic Rome shows the rise, and the later Byzantine art the decline. This view is in accord with history, for Constantinople was New Rome, and here, if anywhere, we should expect to find preserved the traditions of Old Rome.

The division of Western Mediaeval Architecture into the two schools of Romanesque and Gothic presents a parallel case. It is now realised that no logical separation can be made between the two so-called styles. Similarly we may continue to speak of the Classic Roman style and of the Byzantine style, although the two really belong to one great era in the history of art.

CHAPTER II

THE CHURCH OF S. JOHN THE BAPTIST OF THE STUDION, EMIR AHOR JAMISSI

The mosque Emir Ahor Jamissi, situated in the quarter of Psamathia, near the modern Greek church of S. Constantine, and at short distance from the Golden Gate (Yedi Koulé), is the old church of S. John the Baptist, which was associated with the celebrated monastery of Studius, ἡ μονὴ τοῦ Στουδίου. It may be reached by taking the train from Sirkiji Iskelessi to Psamathia or Yedi Koulé. 35

In favour of the identification of the building, there is, first, the authority of tradition, 36 which in the case of a church so famous may be confidently accepted as decisive. In the next place, all indications of the character and position of the Studion, however vague, point to Emir Ahor Jamissi as the representative of that church. For the mosque presents the characteristic features which belonged to the Studion as a basilica of the fifth century, and stands where that sanctuary stood, in the district at the south-western angle of the city,37 and on the left hand of the street leading from S. Mary Peribleptos (Soulou Monastir) to the Golden Gate.38 Furthermore, as held true of the Studion, the mosque is in the vicinity of the Golden Gate,39 and readily accessible from a gate and landing (Narli Kapou) on the shore of the Sea of Marmora.40

According to the historian Theophanes,41 the church was erected in the year 463 by the patrician Studius, after whom the church and the monastery attached to it were named. He is described as a Roman of noble birth and large means who devoted his wealth to the service of God,42 and may safely be identified with Studius who held the consulship in 454 during the reign of Marcian.43

If we may trust the Anonymus, 44 the church erected by Studius replaced a sanctuary which stood at one time, like the Chora, outside the city. Seeing the territory immediately beyond the Constantinian fortifications was well peopled before its inclusion within the city limits by Theodosius II., there is nothing improbable in the existence of such extra-mural sanctuaries, and as most, if not all, of them would be small buildings, they would naturally require enlargement or reconstruction when brought within the wider bounds of the capital. According to Suidas, 45 the building was at first a parochial church; its attachment to a monastery was an after-thought of its founder.

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The monastery was large and richly endowed, capable of accommodating one thousand monks. 46 Its first inmates were taken from a fraternity known as the Akoimeti, 'the sleepless'; so named because in successive companies they celebrated divine service in their chapels day and night without ceasing, like the worshippers in the courts of heaven.