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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.

basilica
In ancient Roman architecture a large oblong type building used as hall of justice and public meeting place. The roman basilica served as a model for early Christian churches.

corinthian order
The most elaborate of the ancient greek architectural orders. It was developed in the 4th century BC in Greece and it was extensively used in Roman architecture. It is similar to the Ionic order. Its capitals being four-sided and composed of a basket-shaped body decorated with volumes and rows of acanthus leaves.

intercolumnar space (or intercolumniation)
The space between two adjacent columns.

ionic order, the
An architectural order devised in Ionia and developed in Asia Minor and the Greek islands in the 6th century BC. Its columns have elaborately moulded bases, fluted shafts (with fillets, ending in fillets), and volute capitals. The entablature consists of an three-fasciae archirave, a continuous frieze, usually richly decorated with reliefs, and a cornice. The Ionic order was more elaborate in dimentions, comparing with the Doric.

macellum
Meat market.

monopteros
A circular building with a single row of columns supporting a roof

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

opus caementicium
Roman technique of constructing structures using concrete. It was spread in the east part of the Roman Empire after 50 BC.

opus incertum
Masonry style where small, irregular stones are used for the wall's facade mixed with plaster.

opus mixtum (ουδ.)
Masonry consisting of small stones and abudant mortar, which often interchange with horizontal double rows of plinths.

orthostate
A course of blocks laid on edge, normally in the lower part of the wall of a building.

polyandreion
Monument in which heroes were buried or at least worshipped.

quadriporticus
four colonnades surrounding a quadrangular square.

spolia
From the Latin word spolium (=spoils, booty). Architectural remains from destroyed buildings that have been reused in later periods.

symbols of the four Evangelists
The four parts of the Tetramorph in Ezekiel’s vision, that is, an angel, a lion, an eagle and an ox, each associated with one of the four Gospels from the 2nd century onwards and at some point considered as the symbols of the four Evangelists (Matthew - Angel; Mark - Lion; Luke - Ox; John - Eagle).

tholos
Circular building with a conical roof.