The earliest human writing was on hard materials such as ivory and clay; later periods wrote on stone, then on leather and papyrus paper; although the ancient Chinese writings were on bronze, or the Indians wrote on palm leaves. The Sumerians wrote on clay, the Achaemenids, Ashkenazim, and Sasanians on stone, and the Egyptians wrote on stone with pictographic lines; each nation had a specific script and wrote on specific materials or objects. Inscriptions were widely used in ancient Iran; during the ancient period of the Achaemenid kings and the middle period, which was mainly the Parthian and Sasanian periods, before the Achaemenids, inscriptions in Sumerian, Elamite, and Mesopotamian cuneiform scripts, as well as Urartian inscriptions, have also been discovered.