Clay formed most ancient Mesopotamian writing tablets. Wet clay was plentiful in the alluvial plains of the Tigris and Euphrates, and scribes could press a reed stylus into it before the tablet dried or was fired.
The resulting tablets preserved many kinds of information, including contracts, receipts, school exercises, royal inscriptions, mathematical calculations, medical recipes, and literary works. Most were not deliberately fired; they hardened naturally, while accidental fires sometimes made them especially durable.
Clay tablets are different from monumental stone inscriptions, which were used for selected public texts and royal displays. They are also different from papyrus, which was used in some other ancient cultures but was not the normal writing surface for Mesopotamian administration. Because clay survives well in dry or burned archaeological layers, modern knowledge of Mesopotamia depends heavily on these records.