Triforium

A triforium is a shallow arched gallery within the thickness of an inner wall, above the nave of a church or cathedral. It may occur at the level of the clerestory windows, or it may be located as a separate level below the clerestory. It may itself have an outer wall of glass rather than stone. Triforia are sometimes referred to, erroneously, as tribunes. Also called a "blind-storey", the triforium looks like a row of window frames without window openings.