The projection of a figure or series of figures above or below a surface.
It is one of the earliest forms of sculpture, and very probably antedates the introduction of sculpture in the round.
Bas-relief (basso-rilievo), or low relief, is a form of relief which projects from a flat surface apparently to a greater degree than is actually the case; it is distinguished from high relief (alto-rilievo), and from demi-relief (mezzo-rilievo).
The lowest of all, which scarcely rises from the surface, is called depressed or flattened relief (rilievo-stiacoiato).
Hollow relief (cavo-rilievo) is a concave form on which the highest part of the outline is no higher than the surface level.
It was practised largely by the Egyptians, whose works are hence known by the Greek derivative koilana-glyphs (hollow carvings), and is often used tinted, as in Egyptian, Assyrian, and Greek art; in Gothic and Renaissance art it was customary to tint wood, terra-cotta, and stucco, but not marble or stone; an example of tinting is the "Annunciation" of Andrea della Robbia.
It is particularly well adapted to the human figure, especially in action, upon friezes, and to a portrayal of a succession of scenes, as in the bronze doors of various Italian baptisteries.
As a purely Christian and Catholic form of art it ranks high, reaching its fullest development in Florence in the baptistery doors, by Ghiberti, and the marble pulpit of Santa Croce, by Benedetto da Majano.
Besides Della Robbia's Bambini in the Hospital of the Innocents, Florence, Donatello's high and low reliefs are admirable, among the best examples of which is the Head of Saint John presented to Herod.
The finest example extant of low relief is that of the frieze around the cella of the Parthenon, much of which may be seen in the British Museum.
Marble, bronze, and terra-cotta are used exclusively in the larger reliefs; in the smaller reliefs precious stones and metals, and ivory, stucco, wood, and enamel are used.
New Catholic Dictionary