Liturgical east and west in the context of "Chevet"

In architecture, an apse (pl.: apses; from Latin absis, 'arch, vault'; from Ancient Greek ἀψίς, apsis, 'arch'; sometimes written apsis; pl.: apsides) is a semicircular recess covered with a hemispherical vault or semi-dome, also known as an exedra. In Byzantine, Romanesque, and Gothic Christian church (including cathedral and abbey) architecture, the term is applied to a semi-circular or polygonal termination of the main building at the liturgical east end (where the altar is), regardless of the shape of the roof, which may be flat, sloping, domed, or hemispherical. Smaller apses are found elsewhere, especially in shrines.

The narthex is an architectural element typical of early Christian and Byzantine basilicas and churches consisting of the entrance or vestibule, located at the west end of the nave, opposite the church's main altar. Traditionally the narthex was a part of the church building, but was not considered part of the church proper.

In early Christian churches the narthex was often divided into two distinct parts: an esonarthex (inner narthex) between the west wall and the body of the church proper, separated from the nave and aisles by a wall, arcade, colonnade, screen, or rail, and an external closed space, the exonarthex (outer narthex), a court in front of the church façade delimited on all sides by a colonnade as in the first St. Peter's Basilica in Rome or in the Basilica of Sant'Ambrogio in Milan. The exonarthex may have been either open or enclosed with a door leading to the outside, as in the Byzantine Chora Church.