From Italian for "round", it's a large & high circular hall in a building, usually surmounted by a dome
[DOC] [TLE] Architectural history exam part 2 at University of North Carolina ... [PAR] Apr 25, 2016 ... Thich stone walls reinforced with buttresses; small windows; round arches; 
barrell .... large and high circular hall or room in a building usually... [DOC] [TLE] Renaissance Architecture: History, Characteristics, Designs [PAR] Italian Renaissance Architecture ...