or MOSAIC WORK, an assemblage of little pieces of glass, marble, precious stones, and other substances, of various colours, cut in prisms, and fixed in a ground of cement, in such a manner as to imitate the colours and gradations of painting. This sort of work was used both for pavements and for ornamenting walls until a comparatively late period in the middle ages. It was much practised by the Byzantine artists, who re-introduced it into Italy. The most famous kinds of mosaic of recent times are the Roman and the Florentine. Pictures in mosaic were wrought at Rome in the eleventh and twelfth centuries. Some of the finest specimens of mosaics in existence are to be found in St Peter's at Rome. The origin of the name mosaic has not been accurately determined. The most probable derivation, however, is from the Greek μωσαῖον, Lat. opus musivum. (See the Glossarium of Du Cange.)