the possibilities of the writing system in classifying signs according to their 'families', inventing new signs, and developing the writing system, but more generally they were also producing a classification of the things that constituted the world which they inhabited, improving their understanding of it. According to Glassner, this indicates that the invention of writing cannot be entirely linked with material considerations. The invention of such a system required reflection on the image and the different senses that a sign could bear, notably for representing the abstract. Art The Uruk period saw a notable renewal, which accompanied substantial changes in the symbolic sphere. This is visible primarily in the artistic media: the forms of pottery became more rudimentary, after the development of the potter's wheel, which allowed mass-production without a focus on decorative elements. Painted pottery is less common than in previous periods, with no decoration or just incisions or pellets. The greater complexity of the society and the development of more powerful elites who wanted to express their power in more diverse ways offered new opportunities to artists who could express themselves in other media. Sculpture took on exceptional importance, whether it was carved in the round, or as bas-relief on steles and especially on cylinder seals which first appeared in the Middle Uruk period. These have been the object of numerous studies because they are very good evidence for the mental universe of the people of this period and a means for diffusing symbolic messages, as a result of the possibility of representing more complex scenes than on stamp seals, since they could be rolled out indefinitely, creating a narration with more dynamism than stamps. The artistic canons of the period were clearly more realistic than the preceding periods. The human being is at the centre of this art. This is notably the case with the cylinder seals and prints of cylinder seals found at Susa (level II), which are the most realistic of the period: they represent the central figure of society as the monarch, but also some ordinary men engaged in everyday life, agricultural and artisanal work (pottery, weaving). This realism indicates a true shift, which might be called 'humanist', because it marks a turning point in Mesopotamian art and more generally a change in the mental universe which placed man or at least the human form in a more prominent position than ever before. It