t,
the apse of the diaconicon, where the sacred vessels were kept. Although
there is proof that the prothesis and the diaconicon were in use at a
very early period, yet many churches of the great period, as for example
S. John of the Studion, SS. Sergius and Bacchus, and S. Sophia,
dispensed with these chambers as distinct parts of the building. They
were also omitted in small churches of a late date, where they were
replaced by niches on either side of the bema. The three apses usually
project from the east wall of the church, but occasionally (p. 248) the
two lateral apses are sunk in the wall, and only the central apse shows
on the exterior. As a rule the apses are circular within and polygonal
without. It is rare to find them circular on both the interior and the
exterior (p. 203), and in Greece such a feature is generally an
indication of late date. An octagonal plan, in which three sides of the
octagon appear, sometimes with short returns to the wall, is the most
common; but in later churches polygons of more sides are used,
especially for the central apse, and these are often very irregularly
set out. Some of the churches of Constantinople show five, and even
seven sides.

_Bema._--The bema is rectangular, and sometimes has concave niches on
each side (p. 130). It is covered either with a barrel or with a
cross-groined vault, and communicates with the prothesis and the
diaconicon.

_Prothesis and Diaconicon._--These chambers are either square (p. 214)
or have a long limb to the east resembling a miniature bema (p. 214).
They are lower than the central apse and the cross arms, so that the
cruciform figure of the church shows clearly above them on the
exterior,[25] though in some churches with galleries small chapels
overlooking the bema are placed above them at the gallery level (S.
Theodosia). They have usually a niche on three sides, and are either
dome vaulted or have cross-groined vaults. The combination of a
cross-groined vault with four niches springing from the vaulting level
is particularly effective. In S. Saviour in the Chora (p. 307) these
chambers are covered with drum domes, pierced with windows, but this
treatment is quite exceptional.

_The Gynecaeum._--In the development of church building, the gynecaeum,
or gallery for women, tends to become less and less important. In S.
Sophia, S. Irene, and S. Theodosia, the gallery is a part of the
structure. In S. Mary Diaconissa (p. 185) it is reduced to