In the lower Euphrates valley, a region subject to strong bioclimatic con- straints, irrigation appears to have been tried out very early, probably in the Halaf period (6000–5100 BC), because of a change in the dynamics of the river. Then in the Early Bronze Age, when the kingdom of Mari became established, a system for exploiting the valley appeared, based on different types of canals using gravity flow (for diversion, irrigation, drainage, navigation), the complexity of which required a long period of development. The various canals, the water intake points and the settlement location choices demonstrate an accomplished knowledge and understanding of the principal dynamics that governed the development of the valley, as well as the remarkable technical inventiveness and adaptability of the inhabitants. The quite complete network that has been discovered in the area of Mari for the 3rd millennium BC seems to figure among the earliest known. As there is no evidence, in the field in lower Mesopotamia, of other such networks, it might be considered as an ‘‘ancestor’’ of the many networks that will come into being in all of the Near East from the 1st millennium BC and especially throughout the last two millennia. It is probably the very first project of large-scale town and country planning that our geomorphological and archaeological surveys, conducted for 9 years, allowed to highlight.