Cuneiform is one of the earliest known forms of written expression. Written on clay tablets by means of a blunt reed for a stylus, cuneiform underwent considerable changes over a period spanning three millennia. Originally, pictograms were either drawn on clay tablets in vertical columns with a pen made from a sharpened reed stylus, or incised in stone. This early style lacked the characteristic wedge shape.
Before cuneiform, clay tokens were used count agricultural and manufactured foods. The tokens were placed in hollow clay containers and the lids were marked with the number of tokens inside by pressing them into the lids as many times as the amount of tokens. Later, it was realized that there was no need for both the tokens and the inscription on the containers, so only the inscription was used. Eventually, this system was streamlined with the introduction of symbols for numbers. For example, to avoid making 100 pictures to represent 100 tokens, a dedicated symbol was used.
The writing originated as a system of pictographs. The markings became successively more sophisticated, and pictographs developed into conventionalized linear drawings. The pictorial representations became simplified and more abstract. The number of characters in use also grew gradually smaller, from about 1,000 unique characters in the Early Bronze Age to about 400 unique characters in Late Bronze Age.
Cuneiform tablets could be fired in kilns to provide a permanent record, or they could be recycled if permanence was not needed. Many of the clay tablets found by archaeologists were preserved because they were fired when attacking armies burned the building in which they were kept.