The method of grouping three arched windows of the same height is adopted in apse windows, each of them occupying one side of the exterior. As the deep, narrow mullions are set radiating, the arch is narrower inside than outside. But this difficulty was overcome, partly by lowering the inner crowns, so that the arch is conical, partly by winding the surface. In the Pantokrator (p. 238), instead of radiating to the centre of the apse, the side and mullions are placed parallel to the axis of the church, thus obviating all difficulty. Generally the centre to which the mullions radiate is considerably beyond the apse, so that any necessary little adjustment of the arch could easily be made.
Triple windows supported on circular columns are not infrequent in the north and south cross arms. Sometimes the central light is larger than the lateral lights, at other times, as in the Pantepoptes, the three lights are equal. The lower part of these windows was probably filled in with a breastwork of carved slabs, as in S. Sophia, while the upper part was filled by a pierced grille. At present the existing examples of these windows have been built up to the abaci of the capitals, but in the church of S. Mary Diaconissa (p. 186) the columns still show the original form on the inside.
_Vaulting._--All Byzantine churches of any importance are vaulted in brick. The only exception to this rule in Constantinople is the little church known as Monastir Mesjedi (p. 264). The different systems of Byzantine vaulting have been so fully treated by Choisy and other authorities, that in the absence of any large amount of new material it is not necessary to give here more than a few notes on the application of these systems in Constantinople. It should always be kept in view that, as these vaults were constructed with the lightest of centering, the surfaces and curves must have been largely determined by the mason as he built, and would not necessarily follow any definite geometrical development. "Il serait illusoire," remarks Choisy, "d"attribuer a toutes les voutes byzantines un trace geometrique rigoureus.e.m.e.nt defini."[30]
[Ill.u.s.tration: PLATE II.
(1) THE MYRELAION (SINCE IT WAS BURNED), FROM THE NORTH-WEST.
(2) THE MYRELAION (SINCE IT WAS BURNED), FROM THE SOUTH-EAST.
(By kind permission of H. M. Dwight, Esq.) _To face page 20._]
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 s.p.a.ce, 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 Choisy[31] 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 s.p.a.ce 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.
[Ill.u.s.tration: FIG. 11.]
The vaulting of the outer narthex of S. Saviour in the Chora ill.u.s.trates 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 s.p.a.ce was thus very much reduced, and over it flat domes are thrown. Their rings are true circles, and as the s.p.a.ce 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 s.p.a.ce in one direction into a slightly oblong s.p.a.ce 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 s.p.a.ce, 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.
[Ill.u.s.tration: PLATE III.
(1) THE MYRELAION (SINCE IT WAS BURNT). INTERIOR, LOOKING EAST.
(By kind permission of H. M. Dwight, Esq.) (2) SULEIMAN AGA MESJEDI, BESIDE S. SAVIOUR PANTOKRATOR.
_To face page 24._]
On the other hand a little pa.s.sage 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 s.p.a.ce 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 s.p.a.ce filled in with longitudinal courses. Like the stairs in the Pammakaristos, this pa.s.sage 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 b.u.t.tresses 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 b.u.t.tresses on the sides; while in SS. Sergius and Bacchus the eight b.u.t.tresses 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 b.u.t.tressing is internal. In S. Irene, where the true drum dome first appears, the b.u.t.tresses 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 b.u.t.tress 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 b.u.t.tresses probably of the ninth century are used at the west end of S. Sophia. The double-flying b.u.t.tress 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 b.u.t.tresses, 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 Shahzade.
But they are generally trifling in size, and are rather ornaments than serious attempts to b.u.t.tress 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 ill.u.s.trations of the method adopted in the construction of walls the following measurements may be given, the sizes being in centimetres:
+---------------------------------------+----------+--------------+ | | Brick. | Joint. | +---------------------------------------+----------+--------------+ | Parecclesion of the Pammakaristos | .08 | .04 | | 4 courses brick, 5 joints | .46 | --- | | S. John in Trullo | .03 | .07 to .09 | | Refectory of the Monastery of Manuel | .04 | .04 to .06 | | 4 course stone, 3 joints | .78 | --- | | 4 courses brick, 5 joints | .30 | --- | | | { .0375 | .052 | | Bogdan Serai | { .035 | .035 | | | { .04 | .04 | | 4 courses stone, 8 joints | --- | .55 to .60 | | 4 courses brick, 5 joints | --- | .43 to .47 | | Sanjakdar, brick | .045 | --- | +---------------------------------------+----------+--------------+
_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 p.r.o.nounced 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 s.p.a.cious 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.
[Ill.u.s.tration: PLATE IV.
(1) S. SAVIOUR IN THE CHORA. BRACKET IN THE INNER NARTHEX.
(2) S. THEODORE. SCULPTURED MARBLE SLAB BUILT INTO THE MINARET OF THE MOSQUE.
(3) S. MARY DIACONISSA. HEADS OF WINDOWS IN SOUTH ARM.
(4) S. MARY DIACONISSA. SCULPTURED SLAB ON THE WEST WALL.
_To face page 28._]
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 cla.s.sic 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 ma.s.sive 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 a.s.signed to that church.
V. The Bird and Basket.--Found in Constantinople, only in S. Sophia.