The Mesopotamian civilization emerged during the period 3700–2900 BCE amid the development of technological innovations such as the plough, sailing boats and copper metal working. Clay tablets with pictographic characters appeared in this period to record commercial transactions performed by the temples.[10] Clay receptacles known as bullae (Latin: 'Bubble'), were used in Elamite city of Susa which contained tokens. These receptacles were spherical in shape and acted as envelopes, on which the seal of the individuals taking part in a transaction were engraved. The symbols of the tokens they contained were represented graphically on their surface, and the recipient of the goods could check whether they matched with the amount and characteristics expressed on the bulla once they had received and inspected them. The fact that the content of bulla was marked on its surface produced a simple way of checking without destroying the receptacle, which constituted in itself an exercise in writing that, despite being born spontaneously as a support for the existing system for controlling merchant goods, ultimately became the definitive practice for non-oral communication. Eventually, bullae were replaced by clay tablets, which used symbols to represent the tokens.
During the Sumerian period, token envelop accounting was replaced by flat clay tablets impressed by tokens that merely transferred symbols. Such documents were kept by scribes, who were carefully trained to acquire the necessary literary and arithmetic skills and were held responsible for documenting financial transactions.[15] Such records preceded the earliest found examples of cuneiform writing in the form of abstract signs incised in clay tablets, which were written in Sumerian by 2900 BCE in Jemdet Nasr. Therefore "token envelop accounting" not only preceded the written word but constituted the major impetus in the creation of writing and abstract counting.
