A gallery of arches above the main arcade in a Gothic church is called a triforium.
The triforium is the middle level of a church’s interior elevation, positioned above the large arches of the nave arcade and below the clerestory windows. It often appears as a narrow passage or shallow gallery, with a repeated row of small arches opening onto the nave.
Its name comes through Medieval Latin from a term associated with openings or passages. Triforia vary greatly: some are substantial walkways, while others are ornamental blind arcades that provide visual rhythm without offering much usable floor space.
The three levels are easy to confuse. The arcade is the lowest major tier, the triforium occupies the middle, and the clerestory is the upper zone that admits light. An ambulatory instead wraps around the choir or apse, while a narthex is an entrance vestibule. In many Gothic interiors, the triforium helps emphasize the cathedral’s vertical structure.