exedra

In architecture, an exedra is a semicircular recess or plinth, often crowned by a semi-dome, which is sometimes set into a building's facade. The original Greek sense (ἐξέδρα, a seat out of doors) was applied to a room that opened onto a stoa, ringed with curved high-backed stone benches, a suitable place for a philosophical conversation. An exedra may also be expressed by a curved break in a colonnade, perhaps with a semicircular seat.