Dome, &c.—Agathias tells us that when Justinian rebuilt the dome it was made higher, and that large alterations were made to the sustaining arches on the north and south sides. Salzenberg cites Theophanes and Zonaras who give the increase of height as twenty and twenty-five feet respectively. If we examine the longitudinal section we shall see that the great semidomes of the hemicycles and the apsoid of the bema show much less of their curvature outside than the present central dome. The windows in these do not stand above a cornice, but are pierced through the vaults at middle height; the domical surface being unbroken by any cornice from springing to crown. The cupola of the baptistery is also continuous with the pendentives. A dome of this kind, however, continuing the pendentives, would seem to be impossibly flat, and would be some thirty feet less than the present height—see A in [Fig. 4], the existing dome rising to B. If a curve between these two be obtained by lowering the crown of the dome about fifteen feet to C, it may be noticed that a straight line tangential to the curve of the eastern apsoid, and also to the great semidome would form similar contact with the dome.
Salzenberg, understanding an account of Cedrenus as to a strengthening of the abutments of the dome to refer to the great buttress masses which rise above the gynaeceum roof, considers that the external parts of these masses were additions made at the time of Justinian’s restoration. These great vertical piles are so essential to the structure, to the logical beauty of the design, and to the staircase service of the building; moreover the preparation for them beneath is so adequate, that we cannot accept this suggestion, and therefore follow Choisy in considering them original. Now Choisy, examining the external base of the dome where it forms a square, found that the four angles had been increased, and that it did not originally form a square, but rose above the piers and the lateral arches as shown in [Fig. 34], and in [Fig. 37], where the first base is shown by hatching and the additions by dotted lines, A A. “This alteration,” he writes, “is not hypothetical. I verified the entire absence of bond between the first base of the dome and the added work” (p. 138). These additions were built on the lateral arches, and on the top of the piers, altering the form shown in our [Fig. 35] to the present form given by Salzenberg. That Choisy is right, is borne out by seeing the resemblance of treatment that there would have been between the growth of the dome on the north and south and the semidome on the west (see [Fig. 34]).
Fig. 34.—View of Vaulted System of S. Sophia, adapted from Choisy.
Again, Salzenberg hardly makes it sufficiently clear that the large arches in the walls which fill the great vertical semicircles over the arcades on north and south sides, are in fact the inner surfaces of the arches which pass between the pairs of piers on north and south sides (seventy-two feet apart in this direction), and being the whole width of those piers (fifteen feet eight inches) on soffite they form the immense arches so well known on the outside. The semicircles of wall, each of which contains twelve windows, are now filled in beneath these arches, flush with their inner faces, and the arches therefore do not show to the interior through the decoration (Figs. [4], [36], [38]).
Fig. 35.—Plan of Upper Gallery as first designed.
Fig. 36.—Section of Aisles and Gallery.
Now Agathias (see page [30]) says that at the restoration after the earthquake in 558, at the north and south arches they brought towards the inside “the portion of the building which was on the curve.” This, we think, must refer to the filling wall, in the arches of seventy-two feet span, which we suppose was formerly on the exterior, and thus left an upper gallery twelve feet wide and seventy-two feet long open to the interior. “And they made the arches wider to be in harmony with the others, thus making the equilateral symmetry more perfect. They thus reduced the vast space and formed an oblong design.” That is the arches of seventy-two feet, when filled up on the inside, were no longer visible, and the dome appeared to stand over arches of 100 feet span on north and south, as already on east and west, the transverse dimension of the church being lessened between these points by some twenty-four feet. Salzenberg understanding Agathias to refer to the apparent arches of 100 feet span on north and south is unable to offer any explanation.