The art of engraving gemstones in sunken relief is named intaglio. Usually the subjects were portraits of either individuals or gods. The carved gemstones would often be mounted on rings and besides a merely ornamental purpose, they could also be used as wax seals in order to confirm the authenticity of written documents. These gems were popular amongst the Ancient Greeks, Romans and also extensively used during the Middle Ages. Carved cylinders used as wax seals in Mesopotamia are usually not referred to as intaglio, although the engraving technique is similar.