[109] Antoniadi, S. Sophia, vol. ii, pp. 7-9, draws attention to the development of buildings with sides turned into exhedrae, from their simplest form to their culmination in S. Sophia. He refers for illustrations to plans in Dehio und Bezold, Die kirchliche Baukunst des Abendlandes, vol. i. pp. 23-31; Atlas, vol. i. plate i. figures 1, 2, 3, 4, 7; plate iii. figures 1, 2, 7.
[110] C. Diehl, Theodora, pp. 242, 342.
[111] The ratio of the height of the gallery above the floor of the church to the height of the summit of the dome is, according to Antoniadi, 1⁄3.5, the same as in S. Sophia as built by Anthemius.
[112] 'Pulvins,' says Rivoira (Lombardic Architecture, p. 11, English translation), 'serve the purpose of providing the springers of the arches with a base corresponding to the wall which they carry, while allowing the support beneath to be much slighter without injuring the stability of the structure.'
[113] Rivoira, ut supra, p. 62: 'The volutes in the Pseudo-Ionic capital intended to conceal the abruptness of the transition from the square of the pulvin to the round.'
[114] De aed. i. p. 187.
[115] 'The centres of the radii of these concave compartments are formed by having three points given the groins on either side and the angle of the octagon in the centre. With these points for each compartment the radius is given, and an arc turned giving the concavity required for each web at its springing.'—A. E. Henderson in the Builder, January 1906, p. 4.
[116] In S. George of Ezra in Syria (515), as Mr. E. M. Antoniadi informs me, the dome overhangs or oversails the angles of the octagon.
[117] 'The dome stands within a polygon of sixteen sides, that rises four metres above the springing line, keeping the dome taut and weighting the haunches. Against this polygonal casing are set buttresses formed by the extension of the piers of the octagon to within m. 11⁄2 from the cornice of the dome. These buttresses are in their turn respectively strengthened, on the rear, by two small buttresses; of which those on the north, south, east, and west sides rest on an arch of the gynecaeum, and carry the thrust to the outer walls of the church, while the others rest on the exhedrae and the vaulting of the gynecaeum. Furthermore, from the summit of the buttresses formed by the piers of the octagon a small buttress is set against the cupola itself up to the cornice.' This marshalling of the buttresses around the dome in three tiers, while securing the stability of the structure, is moreover strikingly artistic. See Fig. [21.]