A polyptych (Greek: 'many folds') is a work of art consisting of multiple panels joined together, typically hinged so they can be opened and closed. The diptych has two panels, the triptych three, and the polyptych four or more. The format was central to medieval and Renaissance altarpiece design, where the outer 'wings' could show different imagery when closed than when open — typically saints or the Annunciation on the outside, and the Crucifixion or other narrative scenes inside. Jan van Eyck's Ghent Altarpiece (completed 1432) is the most celebrated polyptych: its 24 panels, painted on both sides, create two entirely different programmes — a grisaille exterior for everyday viewing and a blazing full-colour interior for feast days. Francis Bacon revived the triptych format in the 20th century for his isolation studies of isolated human figures in space.