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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.

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

corner bays
In a cross-in-square church, they are the four compartements between the arms of the cross, that make inscribe the central cross into a square. They were usually covered with cross-or domical vaults.

cross-domed basilica
Type of domed basilica. A church plan, whose core, enveloped on three sides by aisles and galleries with a transept, forms a cross. The core is surmounted by a dome in the centre.

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.

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.

drum of dome
Part of the church, semicircular or polygonal, on which rises an hemispheric dome

exonarthex (outer narthex)
The transverse vestibule or portico preceding the narthex of the church.

light
(of a window) The arched opening or window in Byzantine churches. Depending on the number of lights, there are single-light, double-light and three-light windows.

maphorion
A women's garment covering the head and shoulders and sometimes reaching down to the feet. In Byzantium maphorion was the name of the Virgin's outer veil. According to the christian tradition it was preserved by apostle Thomas after the Dormition and 4-5 centuries afterwards it was transfered to Constantinople and deposited at the church of Blachernai. It was one of the most important relics gathered in Constantinople.

mihrab
Α niche in a mosque pointing towards Mecca

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

patrikios
(from lat. patricius) Higher title of honour, placed, according to the "Tactika" of the 9th and the 10th centuries, between anthypatos and protospatharios. It was given to the most important governors and generals. Gradually, however, it fell into disuse and from the 12th century did not exist any more.

Synaxarion of Constantinople
A compilation of brief accounts on every saint that was celebrated during a liturgical year, arranged by months. It was one of the first and most thorough compilation of synaxaria and it is considered a valuable source for the Byzantine studies. Its compilation must be dated to the 10th century and was probably linked to the tradition of the Church of Constantinople. It was the model for many synaxaria compiled later (such as the Menologion of Basil II), and it was completed or slightly altered in some parts through the years. It was published in 1902 by the Belgian scholar Hippolyte Delehaye (Synaxarium ecclesiae Constantinopolitanae e codice Sirmondiano [Bruxelles 1902]).

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