the curved inside end of a building, especially the east end of a church (apsis). Semicircular or polygonal termination to the choir, chancel (see cathedral), or aisle of a public building, first used in pre-Christian Roman architecture. Originally a large niche to hold the statue of a deity in a temple, the apse also appeared in ancient baths and basilicas. The domed apse became a standard part of the Christian church plan
of a church, having in the plan a polygonal or semicircular termination, and, most often, projecting from the east end