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.

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.

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

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

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

praefectus urbi (prefect of the city)
(later referred to as the eparch of the city) Αdministrator and virtual governor of Constantinople in the Early/Middle Byzantine Era. He was responsible for the surveillance and the harmonius life of the Capital. One of his responsibilities was to control the commercial and manufacturing activities of Constantinople. After 1204, however, the office began to diminish, while from the 14th century, his responsibilities were assumed by two officers, the so-called kephalatikeuontai of the capital.

vault
A semi-cylindrical roof.