Fig. 7.
Arches.—Though the pointed arch was known and employed in cisterns, as in the Cistern of the One Thousand and One Columns, Bin-bir-derek, the circular arch is invariably found in work meant to be seen. The difficulty attending this form, in which arches of unequal breadth do not rise to the same height, was overcome, as in the West, by stilting, that is, by raising the smaller arches on straight 'legs' to the required height. The stilted arch, indeed, seems to have been admired for its own sake, as we find it used almost universally both in vaulting and in decorative arches even where it was not structurally required. In windows and in the arches connecting the dome columns to the wall stilting is sometimes carried to extremes.
Domes.—The eastern dome of S. Irene, erected about 740 A.D., is generally considered to be the first example of a dome built on a high drum, though S. Sophia of Salonica, an earlier structure, has a low imperfect drum. After this date the characteristics of the Byzantine dome are the high drum divided by ribs or hollow segments on the interior, polygonal on the exterior, and crowned by a cornice which is arched over the windows.[26]
Drumless domes are sometimes found in the later churches, as in the narthexes of the Panachrantos and S. Andrew, the angle domes of S. Theodosia, and in Bogdan Serai. These are ribless hemispherical domes of the type shown in Fig. [8], and are in all cases without windows. The earlier system of piercing windows through the dome does not occur in the later churches, though characteristic of Turkish work.
The three diagrams (Figs. [8], [9,] and [10]) illustrate the development of the dome: firstly, the low saucer dome or dome-vault in which dome and pendentives are part of the same spherical surface; secondly, the hemispherical dome on pendentives; and thirdly, the hemispherical dome with a drum interposed between it and the pendentives.
Fig. 8.—The Saucer Dome Or Dome-Vault.
Flat external cornices on the dome are not uncommon in the later churches of Byzantine Greece, as in S. Sophia at Monemvasia.[27] In Constantinople only one dome with a flat cornice can be regarded as original, that of S. John in Trullo, a church which is exceptional also in other respects. The many other domes in the churches of Constantinople on high drums and with flat cornices are Turkish either in whole or in part. The high ribless domes of the Panachrantos, for instance, circular in plan within and without, with square-headed windows, plain stone sill, and flat cornice in moulded plaster, may be regarded as typical Turkish drum-domes. As will appear in the sequel, the dome over the north church of the Pantokrator and the domes of SS. Peter and Mark, the Diaconissa, and S. Theodosia, are also Turkish.
