The ancient city of Napata in what is now Sudan owes its success to the slowing of the Nile river 4,000 years ago, archaeologists have discovered.
The city was a major urban and cultural centre of Kush, an ancient empire of Nubia.
A study of 12,500 years of Nile history found the city was established when the river’s characteristics changed.
For the first 8,000 years of this period, the Nile carved its own valley. Then, about 4,000 years ago, that valley levelled out, allowing the river to start depositing sediment and building up the valley floor. The river has since been relatively stable, with a layer of fertile clay and silt about 10 metres thick.
The researchers say another geologic feature, the Nile's Fourth Cataract, also helped the river slow and allowed it to drop sediment at the site where Napata would eventually thrive. The cataracts of the Nile are stretches of islands and fast-moving rapids. The Fourth Cataract lies just upstream of Jebel Barkal, a Unesco World Heritage Site and the modern name for Napata.
It was the seat of the Kush empire, an important player in the ancient world, says Geoff Emberling of the University of Michigan and co-leader of the study published in the Proceedings of the National Academy of Sciences.
The empire, mentioned in the Bible by the Greek historian Herodotus, interacted with Egypt, the Assyrians, Greeks, Persians and with the Roman Empire.
After the Egyptian empire collapsed around 1200BCE, the Kushite dynasty came to power and built palaces, pyramids and temples on a sandstone outcrop which is now Jebel Barkal.
The scientists examined the land underlying the city to determine what geological processes might have led to the city's successful settlement.
Their findings suggest Napata, which flourished from about 800BCE to 100CE, owed its staying power to the millennia of clay deposits that built up a thick and fertile floodplain, creating a landscape that reduced the risk of flooding while maintaining access to water.
“Because of a history of relatively lower investment in research in Sudan, some very basic questions haven't been addressed,” Mr Emberling said. “We might think we know all we need to know about the Nile because there's been a fair amount of research in Egypt. But in Sudan, the way the Nile works is different.
“We've missed a key tool to help us not only understand the rise and fall of individual settlements, but also the broader history of the rise and fall of the Empire of Kush. This is really the first systematic geomorphological study in Sudan that relates to these ancient cultures.”
In Sudan, the geology of the region creates rapids, waterfalls and islands along the Nile that disrupt travel and fragment settlements, Mr Emberling said.
Co-leader of the study Jan Peeters added: “Where sediments accumulate shapes where people can live, farm, and carry out cultural and religious practices,”
The research team drilled 26 boreholes across the river valley using a technique called optically stimulated luminescence dating, which dates samples by determining the last time sand grains were exposed to light.
The researchers say this work is continuing, even as Sudan is still embroiled in civil war.
“Despite all the difficulties and hardship of Sudan because of the ongoing war, research is continuing through the efforts of our local collaborators,” Mr Peeters said. “Their work is central to the project, which places strong emphasis on community engagement and collaboration with Sudanese researchers.”
