Mosaic technique used in Hellenistic and Roman times, in which part or all of a figural mosaic is made up of small, closely set tesserae (cubes of stone, ceramic, glass, or other hard material) that permit fine gradations of color and an exact following of figure contours and outlines. The word vermiculatum ("wormlike") refers to the undulating rows of tesserae in this work. Opus vermiculatum was generally used for emblemata or central figural panels which were surrounded by geometrical or floral designs in opus tessellatum a coarser mosaic technique with larger tesserae; occasionally opus vermiculatum was used only for faces and other details in an opus tessellatum mosaic. The earliest known example of opus vermiculatum c 200 BC is an emblema showing a personification of the city of Alexandria. By the 1st century BC Romans had adopted the technique or imported Greek artists to do it; a number of fine opus vermiculatum pieces from this period have been found at Pompeii.