Triforium

thumb|A Romanesque architecture|Romanesque triforium gallery, Cathedral of Saint Mary Major, Lisbon thumb|Interior elevation view of a Gothic cathedral, with triforium highlighted

A triforium is an interior gallery, opening onto the tall central space of a building at an upper level. In a church, it opens onto the nave from above the side aisles; it may occur at the level of the clerestory windows, or it may be located as a separate level below the clerestory. Masonry triforia are generally vaulted and separated from the central space by arcades. Early triforia were often wide and spacious, but later ones tend to be shallow, within the thickness of an inner wall, and may be blind arcades not wide enough to walk along. The outer wall of the triforium may itself have windows (glazed or unglazed openings), or it may be solid stone. A narrow triforium may also be called a "blind-storey", and looks like a row of window frames.