d 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. 1-1/2 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 artis