Exedra

An exedra is a semicircular architectural recess or platform, sometimes crowned by a semi-dome, and either set into a building's façade or free-standing. The original Greek word ἐξέδρα was applied to a room that opened onto a stoa, ringed with curved high-backed stone benches, a suitable place for conversation. An exedra may also be expressed by a curved break in a colonnade, perhaps with a semici... (Wikipedia)