Water acquisition strategies are critical to define and understand the structure of the network of permanent settlements on the arid margins of southern Arabia in antiquity. Two models seem to emerge. The network model of hierarchical agricultural sites is based on long term sedentary communities having shared significant communal work in controlling the flow of water and the building of irrigation systems. The model of combinations of complementary sites took shape in the last centuries Bc in the steppes of eastern Arabia; it results from the movement patterns of people in contact with the nomadic way of life, which sites were distributed along an itinerary rather than throughout a territory.