Whether it's the sacking of Babylon or the fall of the Roman Empire, we often assume the downfall of ancient civilizations comes down to one thing: war.
Historians had assumed the same about another ancient civilization, located in the Otrar oasis in Central Asia. The prevailing history assumed Mongol invaders in the early 13th century led to the demise of this civilization, which once thrived in the lands surrounding the Aral Sea.
But new research published Monday in the Proceedings of the National Academy of Sciences presents a shock alternative ending: Instead of foreign invaders, Mother Nature may have dealt the death blow to this ancient civilization.
Here's the background — Surrounded by two plentiful sources of floodwater — the Amu Darya and the Syr Darya rivers — the ancient Otrar oasis allowed ancient human settlements to flourish and grow.
This ancient river civilization became known as "Transoxania," or "Beyond the Oxus River," another name for the Amu Darya.
Between 650 and 760 A.D., prominent settlements thrived here, fending off multiple invasions by Arab armies. Over time, the site became an important crossroads on Silk Road trading route and a major center of thought and art in the early Islamic renaissance. At its peak, Transoxania was referred to as the “Land of the Thousand Cities."
"The aftermath of the Arab invasions sees a recovery of most settlements in the Otrar Oasis, but not all, followed by another economic boom," Mark Macklin and Willem Toonen, authors on the study, tell Inverse.
But the good times did not last. The beginning of the end of this civilization coincided with the Mongol conquest of the city of Otrar, which occurred in 1218, and the civilization completely collapsed sometime in the 16th-17th centuries.
"The Mongol invasion... had a completely different outcome with limited recovery and this occurred more than 100 years after the destruction of Otrar," Macklin and Toonen explain.
The Big Idea — The theory the Mongol invasion caused the demise of Transoxania seemed like an open-and-shut case. But the researchers questioned whether the Mongol invasions might be more of a coincidence than a cause.
"It’s thought-provoking how rapidly these incredibly agriculturally productive city-states went from boom to bust," Macklin and Toonen say.
Together with their colleagues, they posed an alternative ending: Were natural forces to blame for the fall of this once great nation, rather than the designs of rival civilizations?
This theory was based in part on one of Transoxania's main assets — the rivers.
What they discovered — The archaeologists used two techniques, radiometric dating and optically stimulated luminescence dating, to identify when irrigation canals — which once fed river water into the fields of Transoxania's farmers — in these areas were likely abandoned.
"First, we established when canals became disused by dating sediments that infilled them after they stopped carrying water for irrigation," Macklin and Toonen explain.
The scientists then used these techniques to paint a broader history of river flow in the region.
"Second, using the same radiometric techniques, we dated river sediments in order to reconstruct a history of water flow in rivers that fed these canals," they add.
The radiometric dating confirmed changing river levels affected irrigation systems' effectiveness at the same time as the Mongol hordes advanced — and, ultimately, it may be this, and not the armies, which influenced the survival of the civilization.
If so, it also helps explain why the people of Otrar were able to survive and thrive after the Arab conquests, but not after the Mongol invasions.
"The climatic conditions during, and especially after the Arab and Mongol invasions were very different: wet conditions that were conducive to large scale floodwater farming during and immediately after the Arab invasion; and exceptionally dry conditions — drought — at the time of the Mongol invasion and occupation that were not conducive to irrigation," Macklin and Toonen say.
Why it matters — The researchers are quick to stress: The demise of Transoxania is not an 'either-or' scenario. Warfare, climate change, internal politics, and the decline of the Silk Road all played a role in the end of this civilization.
But for the first time, archaeologists now recognize the significance of climate change in the life and times of this ancient civilization, as well as the vulnerability of irrigation-based systems of farming.
"Prior to our study, climate change was not seen as a potential factor influencing the success or failure of floodwater farmers in this region," Macklin and Toonen say.
"But our new research demonstrates that a decline had already started before the arrival of the Mongols with the gradual abandonment of the irrigation system, agricultural lands, and settlements in the region."
Ultimately, the study brings attention to a little-understood, but highly important area of research: the significance of river systems in climate change.
"We have used similar methodologies to help understand the role of rivers in terms of climate change, major floods, and droughts in the development of ancient river civilizations," Macklin and Toonen note.
What's next — The researchers hope their findings will shed light on the impact of climate change on these lesser-known ancient civilizations.
"For some regions, such as the Indus and Nile Valleys and Mesopotamia, the role of climate change in cultural demise has already been demonstrated. Central Asia by contrast has received very little attention, although it has played a pivotal role in world history," Macklin and Toonen add.
But the study can also help us understand the modern-day implications of climate change.
"One of the major take-home messages from our work, and maybe a lesson for our current anthropogenic climate crisis, is how vulnerable worldwide floodwater farming is to short-term climate change in dryland river environments, such as the Aral Sea," Macklin and Toonen say.
The researchers conclude: "as we are increasingly aware today, without favorable environmental conditions, it’s difficult for societies to rebuild and prosper."
Abstract: The Aral Sea basin in Central Asia and its major rivers, the Amu Darya and Syr Darya, were the center of advanced river civilizations, and a principal hub of the Silk Roads over a period of more than 2,000 y. The region’s decline has been traditionally attributed to the devastating Mongol invasion of the early-13th century CE. However, the role of changing hydroclimatic conditions on the development of these culturally influential potamic societies has not been the subject of modern geoarchaeological investigations. In this paper we report the findings of an interdisciplinary investigation of archaeological sites and associated irrigation canals of the Otrar oasis, a United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage site located at the confluence of the Syr Darya and Arys rivers in southern Kazakh-stan. This includes radiometric dating of irrigation canal abandonment and an investigation of Arys river channel dynamics. Major phases of fluvial aggradation, between the seventh and early ninth century CE and between 1350 and 1550 CE coincide with economic flourishing of the oasis, facilitated by wet climatic conditions and higher river flows that favored floodwater farming. Periods of abandonment of the irrigation network and cultural decline primarily correlate with fluvial entrenchment during periods of drought, instead of being related to destructive invasions. Therefore, it seems the great rivers of Central Asia were not just static“stage sets” for some of the turning points of world history, but in many instances, inadvertently or directly shaped the final outcomes and legacies of imperial ambitions in the region.