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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.

atrium
1. Antiquity: The large, open space within a building, which is envelopped by colonnades.2. Βyzantium: The forecourt of a church in early Christian, Byzantine, and medieval arcitecture. It was usually surrounded by four porticoes (quadriporticus).

baptistery
The building or room used for Baptism. It had a font usually in the form of a cross. After the 6th c. the baptisteries constitute distinct constructions- octagonal, circular, cruciform- detached to the church or its courtyard.

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.

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.

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.

monophysitism
A Christian heresy which developed in the 5th cent. Contrary to the orthodox dogmas, it argued that Christ did not possess two natures, but only one – a human nature. This heresy became widespread in the eastern provinces of the Byzantine Empire (mainly in Egypt) and in Armenia.

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

novel (novella)
Τerm meaning ad verbum "new decree" and used since around the 4th century in order to denote the provisions of the emperors as separate from the organized codes. They were written mainly in Greek and used extensively in the Middle Byzantine Era. Since the days of Komnenoi and after, they were replaced by other more specialized terms and they are very rare in the Late Byzantine era

solea
A wide and oblong elevated passageway in front of the central opening of the chancel screen that reached until the ambo; there stood the deacons and the lectors during the Service.

templon or iconostasis
A structure separating the sanctuary from the main church. At first, it simply divided the nave from the presbytery, but later it became higher, with small columns and an epistyle. From the 11th century onwards, icons were placed between the templon columns and, somewhat later, icons were also placed above the epistyle, thus forming the iconostasis. The templon were originally from marble. Wooden iconostases appeared from the 13th century.

three-aisled basilica
An oblong type of church internally divided into three aisles: the middle and the two side aisles. The middle aisle is often lighted by an elevated clerestory. In the Early Byzantine years this type of church had huge dimensions.