Ancient societies did not all need active rivers to thrive

Around the time that urban societies were developing in Egypt and Mesopotamia between 5,300 and 3,300 years ago, the Indus Civilization was also evolving. Scientists have long believed that the settlements of this era sprung up along the banks of a thriving river, but new evidence shows that a major Himalayan river central to the Indus Civilization was no longer active.

The Ghaggar-Hakra River in northwest India and Pakistan is believed to have dried up due to changes in the climate or shifting tectonic plates. But, prior to this study, scientists did not know exactly when the river ceased. It was assumed that the Indus settlements depended on the river and developed around it.

However, a research team from Imperial College London and the Indian Institute of Technology Kanpur has now provided surprising evidence that the Ghaggar-Hakra was no longer flowing at the time the settlements of the Indus Civilization emerged. The findings of the study suggest that ancient urban societies did not depend exclusively on an active, flowing river system to flourish.

“The findings challenge our current understanding of how urbanization in many ancient civilizations began and grew in relation to natural resources,” said lead author Professor Sanjeev Gupta. “Contrary to current belief, it was the departure of a large river, rather than its arrival, that triggered the growth of Indus urban centers.”

The researchers discovered that a major Himalayan river, the Sutlej River, once flowed in the tracks of the Ghaggar-Hakra River, but abruptly changed course about eight thousand years ago. By the time the Indus people settled into the region, there was only an abandoned large river valley.

The large impression in the ground left behind from the the Sutlej River collected water seasonally from monsoons, providing the Indus settlements with a temporary source of water.

“We now know that, given the right conditions, valleys that have lost their rivers can still serve as a water source,” said study co-author Rajiv Sinha. “The civilization would also not have been threatened by the risk of devastating floods that living next to a big river brings.”

Since most previous research has been focused on the link between rivers drying up and the abandonment of ancient urban centers, the team believes this study may encourage archaeologists to take a new look at the development of settlements in early civilizations. The study is published in the journal Nature Communications.

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By Chrissy Sexton, Earth.com Staff Writer