activities, and long-distance commerce. It has been the focus of archaeological investigation led by Robert McCormick Adams Jr., whose work has been very important for the understanding of the emergence of urban societies in this region. A clear settlement hierarchy has been identified, dominated by a number of agglomerations which grew more and more important over the 4th millennium BC, of which Uruk seems to have been the most important by far, making this the most ancient known case of urban macrocephaly, since its hinterland seems to have reinforced Uruk itself to the detriment of its neighbours (notably the region to the north, around Adab and Nippur) in the final part of the period. The ethnic composition of this region in the Uruk period cannot be determined with certainty. It is connected to the problem of the origins of the Sumerians and the dating of their emergence (if they are considered locals of the region) or their arrival (if they are thought to have migrated) in lower Mesopotamia. There is no agreement on the archaeological evidence for a migration, or on whether the earliest form of writing already reflects a specific language. Some argue that it is actually Sumerian, in which case the Sumerians would have been its inventors and would have already been present in the region in the final centuries of the 4th millennium at the latest (which seems to be the most widely accepted position). Whether other ethnic groups were also present, especially Semitic ancestors of the Akkadians or one or several 'pre-Sumerian' peoples (neither Sumerian nor Semite and predating both in the region) is also debated and cannot be resolved by excavation. Uruk Out of these urban agglomerations, it is Uruk, the period's eponymous site, which was the largest by far, according to our current knowledge, and it is the main one from which the chronological sequence of the period has been constructed. It may have covered 230–500 hectares at its peak during the Late Uruk period, more than the other contemporary large settlements, and it may have had a population of between 25,000 and 50,000 people. The architectural profile of the site consists of two monumental groups located 500 metres apart. The most remarkable constructions are located in the sector called the Eanna (after the temple which was located there in subsequent periods and possibly already at this stage). After the 'Limestone Temple' of level