In Mesopotamia, "cyclical flooding" made possible natural irrigation of cropland and grazing land, which led to an agricultural development that did not need a large infrastructure, as in other cultures of the world, which had to build watering canals and crops. For the cultures from the Land Between Two Rivers, more than six thousand years ago, creating such channels would have been very difficult, but since the rivers overflow periodically, this allowed the farmers of the first cities of the Sumerians (such as Eridu, Uruk, and Ur) know when to plant, when the waters of both rivers arrive, and prosper in States Cities, beginning the sedentary life, and the first civilizations of the world.