An examination of the exterior on the south side shows that the south-west staircase was built before the porch, or the part above it at least, because a straight joint in the walling, and the form of the roofing, here clearly make evident that the apex of the gable roof was originally over the centre of the staircase, and that the slope has been subsequently run forward to cover the part above the porch.
In considering all the other irregularly attached buildings, together with the historical evidence, it seems clear that the church as designed and first built was externally a regular parallelogram, interrupted only by the projection of the apse at the east end; which was itself masked by a range of low chambers against the east wall, through which there were two entrances to the church as at present, and to which other two doors, in the east wall, still visible but now blocked, gave access. The other external doors, besides those from narthex, being two on the north and one in the south wall; together with two external doors at the gynaeceum level, one of which probably gave access to the gallery along which the emperor passed to the church, and the other, to the north, may have led to the cells of the clergy.
Baptistery and Loggia.—Of early buildings detached from the church we have the round building at the north-east, which we regard as having descended from the earlier church, and the south-west baptistery, with a loggia attached to its north side. The space between the church and the baptistery on plan looks like a covered way, leading from the church with a screen in the middle, but the part next the church is, and always must have been, open. The part next the baptistery is covered with a large semicylindrical vault, arched transversely to the “screen,” and penetrated by a less cylinder in the direction of the length of the loggia. Rebates (on baptistery side) round the doorway which stands between the pair of columns show that there was a door, and strips down the sides of the pillars, which stand above the transom, show that pierced slabs or other closures filled the arched front of the vault. If we add breast-high closures in the lateral openings, as in the portico of St. John Studius, the whole becomes an inclosed loggia against the baptistery. Salzenberg states that there was a door in the north wall of baptistery, and Labarte places another in the western compartment of south aisle of church, but for the latter there does not appear to be a particle of evidence; and consequently the court and loggia cannot have formed a direct passage to the baptistery. 1. Salzenberg on his plan draws the transverse axis of the baptistery, and that of the western bay of the church; these do not agree by a foot or two, but the doorway of “screen” agrees with neither, nor is it a mean between them, but varies by excess. 2. In the section (Salzenberg, Plate xi.) it is seen that the present level of floor in this loggia is that of baptistery, and is below that of church; but the columns have no bases, therefore the loggia floor was beneath both church and baptistery. 3. A large arch is shown between the church and west pier of this loggia, from which it springs properly, while at the other end it is cut off incomplete by the wall of the church. These reasons together lead us to suggest that the loggia is possibly older than the church, and that it may be a part of an arcade retained when the present church was built. The style of the screen would readily allow of its being twenty or thirty years older than S. Sophia. The capitals are not found elsewhere in the church, while similar ones form the chief order at S. Sergius; and the door is inserted between the two columns, exactly as in the portico of S. John Studius. We do not however insist on its being earlier than the church so much as on the evidence pointing to its being part of a continuous arcade (see plan, [Fig. 39]). Doubtless it might be determined from a careful examination whether the loggia or the baptistery was built first.
Fig. 39.—Restoration of Loggia by the Baptistery. Scale about eight feet to an inch.
The way by which the “Great Baptistery” was reached from the bema, as mentioned in the Ceremonies was probably by this cloister, which perhaps inclosed one of the courts on the sides of the church, spoken of by Procopius and the Silentiary. The portion drawn by Salzenberg still remains, although sadly plastered over and mutilated.
§ 4. STRUCTURAL SYSTEM AND VAULTING.
The geometrical scheme of this building, which in its final form must be the result of hundreds of adjustments, modifications, and expedients, to meet newly discovered emergencies, is withal so seemingly simple, that it may be read as a bare mechanical solution of the primary conditions.
The great central area, excepting only the narrow bema, is surrounded by two stories of vaults; the thrust of the dome over the square of about 100 feet is not only resisted by these, but by the four immense buttressing masses (or rather chambers for they are built hollow) which, pierced by arches, pass right across the aisles. East and west the dome is sustained by the semidomes of the great hemicycles, and these in turn by the vaults of the three subdivisions of the hemicycles. The thrusts are thus distributed in a regular pyramid. The external wall, which incloses the whole, being built out to the extremity of the great buttress piers of the north and south sides, and the lesser piers east and west, is thus little more than a screen, inclosing the more active parts of the structure.
One of the most remarkable expedients of this marvellously planned building is that by which the vaults of the side aisles,—which, having large spans, necessarily spring comparatively low down—are received on the secondary order of columns, standing behind the pillars of the great order. This allows of the stately colonnade on either side of the central space and those in the four exedras being only controlled by the height of the upper floor, which is forty-four feet above the area as is explained by Figs. [36], [38]. These secondary pillars also transform the spaces left by the exedras into square compartments.