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.

arch, the
A curved structure, as a masonry, that covers openings in the stonework and is capable to supports the weight of material over an open space, as in a bridge, doorway, etc. It is often used as a decorative element.

barrel-vault
vaulted, semi-cylindrical construction used often as roof.

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.

gallery
The upper level of a house where the women resided. In ecclesiastical architecture it is the corridor above the aisles and narthex of a church, from where women attended the Liturgy. Originally (in the Byzantine period) the gallery, having a special entrance, was used exclusively by the emperor and the members of the royal family.

niche
Semi-circular recess on the surface of the wall.