How did the Sumerians develop a written language

The Sumerians were among the 1st to develop the written word. They wrote using cunieform, which is a much more complex version of our modern alphabet involving more characters and much more complex shapes. It was mostly lines built on top of each other in various ways. This was written on clay tablets because the Egyptians had not discovered ways to make papyrus (the rough equivalent of paper) yet. It was chisseled into these tablets and mistakes were permanent. Other than that, the Sumerian written word was developed the only way possible: one word at a time in a probably slow and highly complicated process.