From Italian for "round", it's a large & high circular hall in a building, usually surmounted by a dome
[DOC] [TLE] Architectural Terminology [PAR] In ancient Roman architecture, a large rectangular building used as a ... east end 
of a church, usually a French Gothic cathedral, with its apse, ambulatory, and ... 
Ionic, and Corinthian) developed by the Greeks, with a tall capital composed of ... 
Dome.