The Central Asian Aral Sea Basin and its major rivers, the Amu Darya and the Syr Darya, have been the center of advanced river civilizations and a major hub of the Silk Roads for over 2,000 years. The decline of the region has traditionally been attributed to the Mongol invasion of the early 13th century AD. But a new study, published in The works of the National Academy of Sciences, causes this long-term vision.
Toonen et al. disputes the long-held view that the fall of river civilizations in Central Asia was caused by war and the destruction of irrigation infrastructure during the Mongol invasion. Image credit: National Library, Berlin.
“While the great river civilizations of the Old World have been the subject of archaeological and scientific study for more than a century, ancient urban irrigation-based cultures that developed along the great rivers of Central Asia are virtually unknown,” said co-lead authors Dr. Willem Toonen of Vrije University Amsterdam, Dr. Mark Macklin of Lincoln University and their colleagues.
“In the 1950s and 1960s, archaeologists demonstrated that the Amu Darya and Syr Darya rivers, which flow northwest from the Pamir and Tien Shan Mountains and flow into the Aral Sea, were the centers of thriving urban societies from prehistory to the Middle Ages. Late. “
“The 50,000 km2 It was estimated that the area of land irrigated with drinking water was twice as large as in Mesopotamia. “
“The stagnation of the region at the end of the medieval period is generally attributed to a combination of the destructive Mongol invasion of the early 13th century CE and the gradual decline of the Silk Road trade network.”
However, the hydroclimatic and hydromorphic contexts of these changes are largely unknown, with only a handful of sites being radiometrically dated.
Geomorphology and archeology of the Arys river basin and the Otrar oasis in Kazakhstan: (A) the Arys river basin and research areas; (B) Otrar Oasis with the main irrigation canals and archeological sites; (C) low flow Arys River; (D) the river Badam during the peak runoff; (E) aerial view of irrigation canal forks south-east of Altyn; (F) aerial view of Otrar; (G) bifurcation of the irrigation canal with a fortified settlement; (H) ancient irrigation canal near the town of Arys; (I) Abandoned canals (white arrows) and abandoned agricultural land (black arrows) east of Kuik Mardan. Image credit: Toonen et al., doi: 10.1073 / pnas.2009553117.
Researchers focused on the archeological sites and irrigation canals of the Otrar oasis, a UNESCO World Heritage Site, which was once a Silk Road shopping center located at the confluence of the Syr Darya and Arys rivers in southern Kazakhstan.
They investigated the region to determine when the irrigation canals were abandoned and studied the past dynamics of the Arys River, whose waters fed the canals.
They found that despite the documented destruction of settlements, many sites in the Otrar oasis persisted until the drought-related contraction of the 9th century AD.
The Mongol invasion and destruction of the oasis in 1219 AD, however, came after more than 200 years of reduced rainfall, with evidence of widespread abandonment of the canal.
“Our research shows that climate change, not Genghis Khan, was the ultimate cause of the disappearance of forgotten river civilizations in Central Asia,” said Dr. Macklin.
“I found that Central Asia quickly recovered from the Arab invasions of the seventh and eighth centuries AD. due to the favorable humid conditions. “
“But the prolonged drought during and after the subsequent Mongol destruction reduced the resilience of the local population and prevented the re-establishment of large-scale irrigation-based agriculture.”
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Willem HJ Toonen et al. A hydromorphic re-evaluation of forgotten river civilizations in Central Asia. PNAS, published online December 14, 2020; doi: 10.1073 / pnas.2009553117