A sculpture executed upon and attached to a flat surface. The usual impression produced by an artistic relief is that about one-half of the actual proportions of the object are being seen in their third dimension of depth. Strictly speaking, however, relief sculpture is subdivided into various kinds. In alto-rilievo (Italian for "high relief") the figures are sculptured partly or wholly in the round, that is,they project entirely, or almost entirely, from the surface of the block in which they are cut. The metopes from the Parthenon (Elgin Marbles) now in the British Museum are among the best examples of alto-rilievo. Mezzo-rilievo (Italian for semi-relief; French, demi-relief) presents figures that are rounded to half their natural proportions, but without detached parts. Basso-rilievo (Italian for low-relief; French, bas-relief) is a form of surface-ornamentation in which the projectionis very slight. The finest known specimen of low relief is the frieze around the cella of the Parthenon; large portions of it are to be seen in the British Museum. The lowest kind of relief is that described by the Tuscan term rilievo-stíacciato (depressed or flattened relief). This scarcely rises from the surface upon which it is carved, and is mostly an art of fine lines and delicate indications. Donatello's Florentine Madonnas and saints are among the best examples. Finally cavo-rilievo (Italian for hollow relief; French, relief-en-creux) is a method of concave sculpture in which the highest part or outline is on a level with the surface, while the roundness is considerably below it. Cavo-rilievo was practiced chiefly by the Egyptians whose hollow reliefs are known by the Greek term Koilanaglyphs.