evaluate the impact of the development of southern Mesopotamia, since we have almost no archaeological evidence about it. Moreover, the chronology of this period is far from established, which makes it difficult to date the expansion. It has proven difficult to make the levels at different sites correspond closely enough to attribute them to a single period, making the elaboration of relative chronology very complicated. Among the theories that have been advanced to explain the Uruk expansion, the commercial explanation is frequently revived. However, although long-distance trade is undoubtedly a secondary phenomenon for the south Mesopotamian states compared to local production and seems to follow the development of increased social complexity rather than causing it, this does not necessarily prove a process of colonisation. Some other theories propose a form of agrarian colonisation resulting from a shortage of land in Lower Mesopotamia or a migration of refugees after the Uruk region suffered ecological or political upheavals. These explanations are largely advanced to explain the sites of the Syro-Anatolian world, rather than as global theories. Other explanations avoid political and economic factors in order to focus on the Uruk expansion as a long term cultural phenomenon, using concepts of koine, acculturation, hybridity and cultural emulation to emphasise their differentiation according to the cultural regions and sites in question. P. Butterlin has proposed that the links tying southern Mesopotamia to its neighbours in this period should be seen as a 'world culture' rather than an economic 'world system', in which the Uruk region provided a model to its neighbours, each of which took up more adaptable elements in their own way and retained some local traits essentially unchanged. This is intended to explain the different degrees of influence or acculturation. In effect, the impact of Uruk is generally distinguished in specific sites and regions, which has led to the development of multiple typologies of material considered to be characteristic of the Uruk culture (especially the pottery and the beveled rim bowls). It has been possible to identify multiple types of site, ranging from colonies that could be actual Urukian sites through to trading posts with an Urukian enclave and sites that are mostly local with a weak or non-existent Urukian influence, as well as others where contacts are more or less strong without supplanting the local culture. The case of Susiana and the Iranian plateau, which is generally studied by different scholars