Mosaic, and by extension mosaicists, were in high demand in the ancient Mediterranean world. Popularized by the Greeks with the pebble-mosaic technique about the fifth century B.C.E., the art form evolved with the introduction of tesserae. The use of minuscule triangle or cube shapes of coloured glass moved mosaics from the floor to the walls, and allowed for greater colour exploration by mosaicists. The medium was adopted by early Christian art, which made of it the leading pictorial art form in Byzantium from the fourth century to the fourteenth century.