It was the Sutlej, not the “lost” Saraswati river, as some believed, that gave rise to the great Indus civilisation that flourished around 4,000 years ago, a team of Indian and British researchers has found.

The findings, derived from new geological evidence gathered by an international team of scientists led by Sanjeev Gupta, a geologist with Imperial College London, may have significant bearing on our understanding of how the ancient urban civilisation bloomed and ended.

Unlike other civilisations such as Mesopotamian and Egyptian, which came up on major river banks, the Indus civilisation flourished along a course which the Sutlej abandoned some 8,000 years ago, the scientists reported in the journal Nature Communications on Tuesday. Archaeological evidence gathered from excavated Indus civilisation sites in India and Pakistan has shown that the ancient urban settlements came about 4,600 years ago.

“Previously it was supposed that early urbanisation required access to perennial rivers. But the urban centres of the Indus civilisation (also known as Harappan civilisation) developed without the water provided by a big Himalayan river,” said Gupta.

Through meticulously carried out sediment studies and remote sensing, the scientists identified that the present-day Ghaggar, (called Hakra in Pakistan), which is a seasonal river, flows through the former course of Sutlej. “But our detailed dating of the river sediments shows that the river was flowing there at the time of the Indus settlements. The Sutlej had diverted several thousand years earlier than that,” said Gupta.

Earlier claims The study calls into question the contention of a section of archaeologists that the settlements might have developed along the “lost” river of Saraswati. It may debunk some of their arguments to “establish” it was indeed Saraswati, not Ghaggar, that supported the ancient civilisation. For instance, the “proponents” of Saraswati had argued that there was enough geological and sedimentary evidence to show that the river that fed the Indus civilisation carried glacier headwaters. Ghaggar, they contested, could not have been that river, originating as it does from the Shiwaliks in the foothills of the Himalayas.

The new study has emphatically resolved this mystery, showing that these geochemical signatures of glacial origins may have been left behind by the Sutlej, which originates in the ice-capped mountains.

“Our findings are contrary to earlier statements of scholars, but they did not have the hard scientific data. Our dating evidence is very clear,” Gupta told BusinessLine from London.

Turning point “Many believed that it was the death of a river that led to the collapse of the civilisation. But what we find is that it was the demise of a river (by changing of its course) that helped nourish this civilisation,” said Rajiv Sinha, a professor of earth sciences at IIT-Kanpur, who contributed to the study. “In that sense this is a major turning point in our understanding of our past.”

The Sutlej did beget the Indus civilisation in some ways, the scientists said. “When the river changed its course, it left a former channel in the landscape which was a topographic low. This served to capture and concentrate monsoon-fed river flow and contained excellent soils for agriculture. Thus the Sutlej formed the environmental template for the civilisation in this region,” said Gupta.

This was further borne out by the fact that some of these ancient settlements — such as Banawali in Fatehabad district of Haryana — were actually built within the paleochannel, and had the river been active they would have been destroyed by floods.

“This is a very good study which used two different techniques of geochemical fingerprinting with a large number of samples,” said Suvret Kher, an Indian geologist well known for his scientific blogs.

He said the findings were in line with two other major studies carried out in the past. “All three converge on the same answer, that the Sutlej diverted to its present course 8,000 to 10,000 years ago, thousands of years before the advent of the Harappan civilisation,” Kher said.

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