An earlier generation of historians and archaeologists saw this as evidence of an invasion of the settled lands of the Fertile Crescent by desert nomads. We know, however, that a portion of the population of Mesopotamia was Amurru long before the time of the posited invasion. They were pastoralists and nomads living side-by-side with the urban and farming population. When the urban culture of the Early Bronze Age collapsed in the last quarter of the third millennium, some of these people were evidently able to gain positions of influence, and they seem to have taken the lead in the gradual reurbanization that occurred in the early centuries of the second millennium.