Clay tablets are less durable than stone, but make up for this by being easier to shape, cut, and carve, and lighter (and thus easier to transport and store). Clay has the useful characteristic of being soft and malleable when wet, allowing it to be made into the desired shape and imprinted with writing, and then dries into a more stable form. If fired in a kiln, it becomes very hard and durable (though also brittle, so that it can smash if dropped).
Clay tablets were widely used in some ancient civilizations, particularly the Sumerians who used a form of writing called cuneiform which was specifically adapted to this medium, consisting of shapes made from imprinted wedges. The later invention of papyrus, parchment, and paper proved to be a more useful medium for writing, leading to the demise of clay tablets. Many of them survive from ancient times, however, being more long-lasting than the newer media which are subject to rotting, burning, and crumbling.