The Sumerian picture-writing was called cuneiform. Because the Sumerians lived between two rivers, they had plenty of damp clay. Instead of carving their cuneiform onto stone, they would mold this clay into square tablets. Then, while the clay was still wet, they would use a sharp knife or stick to make the cuneiform marks. After the message was carved into the clay, the Sumerians could either wipe it out and write another message (if the message was something unimportant, like a grocery list), or else bake the clay until it was hard. Then the message would last for a very long time.
