CLAY TABLET: The main writing material used by the scribes of early civilizations. Signs were impressed or inscribed on the soft clay, which was then dried in the sun. The ancient Sumerians, Babylonians, Assyrians, and Hittites wrote on tablets made from water-cleaned clay. A common form was a thin quadrilateral tile about 12.5 cm (5 inches) long which, while still wet, was inscribed by a stylus with cuneiform characters. By writing on the surface in small characters, a scribe could copy a substantial text on to a single tablet. For longer texts, several tablets were used and then linked by numbers or catchwords. Book production on clay tablets probably continued for 2000 years in Mesopotamia and Asia Minor. Either dried in the sun or baked in a kiln, clay tablets were almost indestructible. The latter process was used for texts of special value, legal codes, royal annals, and epics to ensure greater preservation. Buried for thousands of years in the mounds of forgotten cities, they have been removed intact or almost so in modern archaeological excavations. The number of clay tablets recovered is nearly half a million, but there are constantly new finds.