Baroque coffered ceiling of the cupola of S. Carlo alle Quattro Fontane, Rome, designed by elipsis
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A coffer (or coffering) in architecture, is a sunken panel in the shape of a square, rectangle, or octagon in a ceiling, soffit or vault. A series of these sunken panels were used as decoration for a ceiling or a vault, also called caissons ('boxes"), or lacunaria ("spaces, openings"), so that a coffered ceiling can be called a lacunar ceiling. The stone coffers of the ancient Greeks and Romans are the earliest surviving examples, but a seventh-century BCE Etruscan chamber tomb in the necropolis of San Giuliano, which is cut in soft tufa-like stone reproduces a ceiling with beams and cross-beams lying on them, with flat panels fillings the lacunae. Wooden coffers were first made by crossing the wooden beams of a ceiling in the Loire Valley châteaus of the early Renaissance.
Experimentation with the possible shapes of coffering, which solve problems of mathematical tiling, or tessellation, were a feature of Islamic as well as Renaissance architecture. The more complicated problems of diminishing the scale of the individual coffers were presented by the requirements of curved surfaces of vaults and domes.