The _voussoirs_ of the lateral dome arches should be noticed. They do not radiate to the centre, but are laid flatter and radiate to a point above the centre. This form of construction, occurring frequently in Byzantine arches, is regarded by some authorities as a method of forming an arch without centering. But in the case of the lateral wall arches before us it occurs where centering could never have been required; while the apse arch, where centering would have had structural value, is formed with true radiating _voussoirs_. The failure of the _voussoirs_ to radiate to the centre therefore seems to be simply the result of using untapered _voussoirs_ in which the arch form must be obtained by wedge-shaped joints. For if these joints are carelessly formed, the crown may very well be reached before the requisite amount of radiation has been obtained. On the other hand, if full centering had been used, we should expect to find marks of the centering boards on the mortar in the enormously thick joints. But neither here nor in any instance where the jointing was visible have such marks been found. Still, when we consider the large amount of mortar employed in Byzantine work, it seems impossible that greater distortions than we actually meet with in Byzantine edifices would not have occurred, even during the building, had no support whatever been given. It seems, therefore, safe to assume the use of at any rate light scaffolding and centering to all Byzantine arches.[500] [Illustration: FIG. 98.] [484] [Greek: Meta tên halôsin], p. 61; cf. Paspates, p. 361. [485] _Tagebuch_, p. 456. [486] Hypselantes, _ut supra_, p. 638. [487] Archaeological Supplement to the _Proceedings of the Greek Syllogos of C.P._ vol. xviii. p. 8. [488] Phrantzes, p. 307. [489] _Tagebuch_, p. 456. [490] See Chap. XII. [491] P. 360. [492] Constant. Christ. iv. p. 162. [493] See Archaeological Supplement to the _Proceedings of the Greek Syllogos of C.P._ vol. xviii. p. 8. [494] Ruy Gonzalez de Clavijo in 1403, _Vida de Gran Tamorlan y itinerario_, p. 50 (Madrid, 1782): 'San Juan del a Piedra está cerca del palacio del Emperador' (_i.e._ near the palace of Blachernae). [495] Miklosich et Müller, i. ii. pp. 21-23. [496] Ducas, p. 288. [497] _De top. C.P._ iv. c. 4. [498] _Tagebuch_, p. 455. [499] When Paspates (p. 360) visited the chapel, the eikons were more distinctly visible than at present, although they bore marks of deliberate injury by Moslem iconoclasts. [500] See p. 23. CHAPTER XXIII THE CHURCH OF S. SAVIOUR IN THE CHORA, KAHRIÉ JAMISSI