Cosmati Artists active in Rome between the 12th and 14th century. Cosmati were essentially a school of marble workers, mosaicists and sculptors. They were two of several families e.g. the Cosmas, and the Cosmatus, working in the same style. The Cosmati began to sign their pieces, a practice which was unusual at the time and represented a clear departure from the medieval craftsman. The term is often used and abused to designate decorative art of the 13th cetury Rome in mosaic work in marble and with inlays of coloured stone and glass.