Qustul ruled two hundred kilometres out from the river on both sides

Remains from sites in what is now the Western Desert, and from country east of the Nile into the Eastern Desert, put the reach of the Qustul state at a hundred to two hundred kilometres out from the river in either direction, along with a long stretch of the valley itself. Inside that territory the cemeteries do the talking. Where the graves sit and how they are laid out show well-developed classes, with royal and religious elites marked off and a king holding temporal and sacred power together. Those are the structural features historians use to identify an early state: stratification, sacral monarchy, an elite of administrators and priests, and territory held at a distance. Qustul had all of them in the middle of the fourth millennium BCE, centuries before Egypt was unified. The template the first pharaohs worked from was already in operation upriver while they were still local rulers of a stretch of floodplain.

Around the thirty-fourth century BCE the climate of the eastern Sahara turned sharply drier and stayed that way. Steppe and semidesert grassland that had carried herds for millennia became the desert it is now, though patches held on well enough to support marginal livestock raising as late as about 2000 BCE. The pastoralists living out there had to go somewhere. They moved out of the emerging desert and settled among the communities already living along the Nile. That is the event that produced the Egypt of the textbooks, the thin green ribbon dependent on an annual flood. Before it, this was open country with mobile herders and a river running through it. After it, thousands of people and their cattle were compressed onto a floodplain a few kilometres wide. The competition for land and the density of population that followed drove polities to grow and swallow one another until the whole valley was unified around 3100 BCE.