Intaglio refers to the technique of engraving gemstones in sunken relief, often exhibiting portraits. Intaglios would often be mounted into a ring and could be used as wax seals in order to confirm the authenticity of written documents. Popular since the ancient Greeks, intaglio carving was popular throughout the roman and medieval period. Carved cylinder seals from ancient Mesopotamia, though an essentially identical technique, are most often not included in the term intaglio.