ambulatory (byz. arch.)
A continuous passage that envelops the naos or the centrally planned core of a structure. In a cross-domed church, where the dome is supported on four masonry piers and between each pair of piers two columns are inserted, the ambulatory is formed by the lateral aisles and western part of the church. Later on, an ambulatory could also envelop a cross-in-square core. During the Palaeologan period, ambulatories, usually serving as funerary chambers, were added to many middle-Byzantine churches of Constantinople.

apse
An arched srtucture or a semi-circular end of a wall. In byzantine architecture it means the semicircular, usually barrel-vaulted, niche at the east end of a basilica. The side aisles of a basilica may also end in an apse, but it is always in the central apse where the altar is placed. It was separated from the main church by a barrier, the templon, or the iconostasis. Its ground plan on the external side could be semicircular, rectangular or polygonal.

arcosolium
(lat.) A tomb carved out of a wall (solium) with an arched niche (arcus) above it.

bema
The area at east end of the naos in Byzantine churches, containing the altar, also referred to as the presbetery or hierateion (sanctuary). In these area take place the Holy Eucharist.

cistern
A receptacle for holding rainwater, but also water transported from elsewhere, in order to keep it stored. The cisterns were either covered eiter open, and they could have more than one compartements.

cross- (groin-) vault
A vault formed over square or rectangular spaces by the interpenetration of two barrel-vaults of equal hight and diameter. The lines of the intersection form a diagonal cross.

cross-in-square church
Type of church in which four barrel-vaulted bays form a greek cross; the central square of their intersection is domed. The cross is inscribed into the square ground plan by means of four corner bays.

Deesis
Iconographic theme, an image of intercession for the salvation of the human race, which represents Jesus as the central figure, between the Virgin and St. John the Baptist

dome
A characteristic element of Byzantine architecture. The dome is a hemispherical vault on a circular wall (drum) usually pierced by windows. The domed church emerges in the Early Byzantine years and its various types gradually prevail, while they are expanded in the Balkans and in Russia.

katholikon
The main church in a monastic complex, heart of the monastic activity.

medallion
In byzantine painting the term indicates the circle containing representations of the busts of holy figures, floral or geometrical patterns as well as inscriptions.

naos (nave)
The main part of the temple, between the narthex and the bema. It was the place where the congregation took part in the liturgy.

narthex
A portico or a rectangular entrance-hall, parallel with the west end of an early Christian basilica or church.

parekklesion
A chapel of small dimensions attached to a foundation or a larger church. Byzantine chapels were often used a burial places.

pendentive
Triangular surface used for the transition from the square base of the church to the hemispheric dome.

recessed brick technique
A masonry technique in which bands of wider and smaller bricks are alternated. The smaller bricks rows are slightly recessed and covered with mortar, thus creating an alternation of red (brick) and light-colored (mortar) surfaces.

tympanum (lunette)
(Rom., Byz.) The arched panel (lunette) inside an arch or an arcosolium.