is type in Constantinople do not differ from the numerous churches of
the same class in the provinces.[19]

A lobed cruciform plan is found in only one church in Constantinople,
that of S. Mary of the Mongols (p. 277). Here the central dome is
supported on four piers set across the angles of the square, so that the
pendentives do not come to a point as usual, but spring from the face of
the piers. Against each side of the square a semi-dome is set, thus
producing a quatrefoil plan at the vaulting level.

Both trefoiled and quatrefoiled churches are not uncommon in Armenia,
such as the cathedral at Etschmiadzin;[20] trefoiled churches of a later
date are found in the western provinces, and examples have been
published from Servia,[21] Salonica,[22] and Greece.[23]

An unusual form of the cross plan is seen in the building known as
Sanjakdar Mesjedi (p. 267), where a cross is placed within an octagon.
Probably the building was not originally a church. It resembles the
octagon near the Pantokrator (p. 270), and may, like it, have been a
library.

_Single Hall Churches._--The plans hitherto considered have all been
characterised by the presence of aisles, galleries, or other spaces
adjoining the central area. The churches of the present class consist
simply of an oblong hall, terminating in an apse, and either roofed in
wood, or covered with domes placed longitudinally, and resting to north
and south on wall arches. Examples of this plan are found in Monastir
Mesjedi (p. 264), S. Thekla (p. 211), Bogdan Serai (p. 284), and in the
memorial chapels attached to the Pantokrator (p. 235), and the Chora (p.
309). In the case of these two memorial chapels, their narrow,
long-stretched plan is evidently due to the desire to keep their eastern
apses in line with the east end of the churches they adjoin, and at the
same time to bring the western end to the narthex from which they were
entered. They are covered with two domes, a system perhaps derived from
S. Irene (p. 94). Kefele Mesjedi (p. 257), which at first sight
resembles a single hall church roofed, in wood, was a refectory. Its
plan may be compared with that of the refectory at the monastery of S.
Luke at Stiris.[24]

II. ARCHITECTURAL FEATURES AND DETAILS

_Apses._--A fully developed Byzantine church terminated in three apses:
a large apse, with the bema or presbytery, in the centre; on the right,
the apse of the prothesis where the sacrament was prepared; on the lef