In the very early years of Mesopotamian life, there was a token exchange system. Tokens (often small clay cones) would be given in receipt for goods or services. This system was in use at least as early as 3500 B.C.E., during the Neolithic period.
The token system evolved into a use of “bullae” or hollow clay balls used for inserting the tokens. Cylinder seals made from stone were used as early as this period. An impression would be carved into a stone and it would be rolled over the clay of the balls, making an impression that would stand for its user’s signature.
By 3300 B.C.E., the tokens were fully enclosed in the bullae, and the bullae would be stamped with information about the enclosed tokens. Early on, this information was simple and usually only showed the numbers of the objects inside. As this technology evolved, the information became more detailed and began to show pictures of objects being traded or of the tokens themselves. These symbols are called pictographs: they would symbolize a donkey, for example, or food.
These pictographic signs were gradually standardized into about 600 symbols. They are the basis for later evolution of cuneiform script. By 3000 B.C.E., scholars believe that the signs that stood for objects or ideas actually also signified the sound of the object: in this way, speech became connected to what was written. Initially this was used only for personal names, but after a few hundred years, writing evolved into full expression of the spoken word.