hird to
the crown of the dome. The groins stop short a little below the dome's
apex, where they are arched into one another, leaving a saucer-shaped
crown now capped by a Turkish finial. The dome is covered with lead, and
presents an undulating surface owing to the protuberance of its eight
concave compartments.[117]

The system of weighting and buttressing the dome displays great skill,
and will be best understood by studying Mr. Henderson's geometrical and
constructive sections of the systems (Figs. 28, 29).

[Illustration: FIG. 22.--BRICK STAMPS IN SS. SERGIUS AND BACCHUS.
(From rubbings by Mr. A. E. Henderson.)
_At east end of south aisle._
_In the gallery._]

[Illustration: FIG. 23.]

[Illustration: FIG. 24.]

[Illustration: FIGS. 25, 26, AND 27.]

[Illustration: FIG. 28.]

[Illustration: FIG. 29.]

[Illustration: FIG. 30.]

[81] Procop. _De aed._ i. c. 4; Banduri, iii. p. 45.

[82] _De top._ ii. c. 14.

[83] Cedren. ii. pp. 642-43.

[84] Mansi, viii. col. 1010.

[85] Banduri, iii. p. 45. The church was visited by Russian pilgrims
in 1200, 1350, 1393.--_Itin. russes_, pp. 160, 120, 164.

[86] Procop. _De aed._ i. p. 186. S. Peter 'near the palace' is
mentioned in the list of abbots at the Synod of C.P. in 536. Mansi,
viii. col. 930, col. 939. Another document of the same Synod, col.
1010, is signed by Peter, hegoumenos of SS. Peter and Paul and of the
holy martyrs SS. Sergius and Bacchus.

[87] Diehl, _Manuel d'art byzantin_, p. 31. Antoniadi has drawn my
attention to the junction of a basilica and a hexagonal building in a
baptistery at Tivoli. See Dehio und Bezold, _Atlas_, plate i. fig. 10.

[88] Synax, Oct. 7.

[89] Du Cange, iv. p. 135.

[90] Cedren. i. p. 635; Procop. _Secret History_, c. 6; Procop. _De
aed._ ii. p. 234; Theoph. p. 339; Theoph. Cont. p. 154.

[91] Cedren. i. pp. 642-43. The Synaxaria (Sirmondi) speak of three
churches of S. Sergius, in or near Constantinople; [Greek: en tais
Sophiais], Oct. 7; [Greek: plesion tes Aetiou kinsternes, Nov. 9 (near
Monastery of Manuel, p. 258); [Greek: peran en Rhouphinianais], May 29
(near Kadikeui).]

[92] Page 220.

[93] Baronius, _Annales ecclesiastici_, tom. ix. p. 253, Luccae, 1741:
'quam basilicam eorum hic in domo nostra sub nomine praedictorum
venerabilium constructam, illustrare et illuminare large dignemini.'

[94] _Ibid._ p. 254.

[95] _De aed._ i. p. 186.

[96] _Ut supra_, [Greek: kai epeita ka