IRON AND STEEL.) In architecture, cupola is primarily a dome-shaped covering for a building or room, especially when the curvature is slight; thus, in fortifications, a low, flat turret resembling an overturned saucer, in which guns are mounted. By extension the term has come to mean a lantern (q.v.) crowning a dome as well as the dome itself, and hence any small, lantern-like form, projecting above the roof of a building.