In the earliest days of human civilization, the ancient Sumerians began keeping records of the crops they grew, goods they traded, taxes collected, wars fought, and kings who ruled them. Because Mesopotamia does not have abundant forests from which to make paper, the Sumerians dug clay out of the riverbeds and used clay tablets to write important information.
The characters were formed by pressing a sharpened reed stylus into the wet clay to make triangle-shaped impressions. In fact, the writing is called cuneiform from the Latin word cuneus, which means "wedge-shaped."
The tablets would be sun-baked, or fired in kilns to last a long time. It worked, because we have examples of cuneiform tablets that are around 5,000 years old! We'll be seeing some when we take our field trip to the Museum of Fine Arts in Boston this spring.