Apse

In architecture, an apse (pl.: apses; from Latinabsis, 'arch, vault'; from Ancient Greekἀψίς, 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 GothicChristianchurch (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.