The graves at Nabta Playa show a ranked society with priests

The megaliths at Nabta Playa carry political information as well as ritual information. The burials around them are uneven. Grave goods and placement separate people by rank, which means the community using the site was stratified by the fifth millennium BCE. Somebody had to know which star rose where and when, which implies a group of specialists trained in that knowledge and holding the ritual duties that went with it. Somebody had to organise the quarrying, hauling and raising of heavy stone, which implies authority over labour. Ehret reads the site as the ritual centre of a polity, most likely of the sacral type that Nilo-Saharan peoples were already practising, where the ruler holds religious and temporal power at once. Ranked burials, a trained priesthood, sacral rule and monumental building are the standard checklist for a complex society. All four are present in the desert a thousand years before Egypt was unified.

Three hundred kilometres southwest of Aswan, in country that is now open desert, there was a lake that filled in the rains. By the middle of the fifth millennium BCE the people who watered cattle there had turned the place into a ritual centre. They erected megalithic arrays, including a circle of stones that works as a calendar and five separate alignments, each pointed at the rising position of a particular star. Every material indication at Nabta Playa and across the wider region says the builders were Nilo-Saharan speakers, the same livestock-raising communities whose pottery and burial customs were moving north down the Nile. The date is the point. The Great Pyramid at Giza went up a full thousand years after these stones were set. The astronomy that later gets described as an achievement of the Egyptian priesthood was already being practised by African pastoralists in the desert, who read the sky closely enough to fix its motions in stone.