This collapse of rain-fed agriculture in the Upper Country meant the loss to southern Mesopotamia of the agrarian subsidies which had kept the Akkadian Empire solvent. Water levels within the Tigris and Euphrates fell 1.5 meters beneath the level of 2600 BC, and although they stabilized for a time during the following Ur III period, rivalries between pastoralists and farmers increased. Attempts were undertaken to prevent the former from herding their flocks in agricultural lands, such as the building of a wall known as the "Repeller of the Amorites" between the Tigris and Euphrates under the Ur III ruler Shu-Sin. Such attempts led to increased political instability; meanwhile, severe depression occurred to re-establish demographic equilibrium with the less favorable climatic conditions.