Apse

__Apse__**:** is a a semicircular recess covered with a hemispherical [|vault] or [|semi-dome]. In [|cathedral] and [|church] [|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).

6th century Byzantine mosaic in the apse of the basilica of [|Sant'Apollinare in Classe] ([|Ravenna], Italy)