Around 2,700 years ago in what is now northern Iraq, the Assyrian Empire was at its zenith, dominating the cultural and political landscape of the Fertile Crescent. But within a few years, the empire collapsed, leaving the once thriving capital of Nineveh abandoned for nearly 200 years. The cause of this catastrophe is an enduring mystery, but a climate record preserved in a cave formation now is revealing that the timing of the empire’s rise and fall coincided with a wet period followed by a 125-year-long megadrought.
Among scholars of Mesopotamia, the fall of the Assyrian Empire is considered the “mother of all catastrophes,” said Harvey Weiss, an archaeologist at Yale University in New Haven, Conn., and an author of the new study. But despite its infamy, numerous questions remain about what triggered the collapse and why recovery of the region took over 100 years, he said. “These are long-standing questions that have dogged archaeologists for over a century” since excavations revealed the abrupt and widespread scale of the Assyrian abandonment.
Changes in climate may seem like an obvious culprit, but a lack of paleoclimate records for the region kept serious inquiries at bay, said lead author Ashish Sinha, a paleoclimatologist at California State University, Dominguez Hills. “Due to war and political instability, hardly any work has been done in this region since the 1980s,” he said. “The paleoclimate records that were available were low resolution and poorly dated, obscuring this pivotal time period surrounding the Assyrian collapse.”
“It All Makes Sense Now”
The new study relies on a limestone stalagmite called a speleothem recovered from the Kuna Ba cave in northeastern Iraq, about 300 kilometers southeast of the modern city of Mosul, just across the Tigris River from the ruins of Nineveh. By tracking the ratios of oxygen and uranium isotopes, which are sensitive to variations in precipitation and temperature, the team was able to reconstruct a high-resolution record of nearly 4,000 years of paleoclimate history for the region.
Researchers then aligned the precipitation records with archaeological and written cuneiform records and found a remarkable correlation: The rise and zenith of the Assyrian Empire, from 920 to 730 BCE, occurred during a period of higher-than-average rainfall, deemed the Assyrian megapluvial, that lasted from 925 to 725 BCE. And the fall of the empire, between 660 and 600 BCE, falls within the peak drought period that lasted from 675 to 550 BCE. This 125-year megadrought helps explain why Nineveh was not resettled for over a century after its abandonment, Weiss said.
“The Kuna Ba record is nothing short of a revelation,” Weiss said. “It all makes sense now. No wonder they left and didn’t come back. Of course, the question of where they went is still a mystery. We may have resolved some long-standing questions, but we’ve also opened many doors to new ones. This is a whole new frontier.”
Archaeological evidence indicates that other cultures in the region did not appear to have been as affected by the megadrought as the Assyrians were, Weiss said. “Assyria was an agrarian society dependent on seasonal precipitation for cereal agriculture. To the south, the Babylonians relied on irrigation agriculture, so their resources, government, and society were not as affected by the drought.”
This distinction helps explain why the relatively small Babylonian and Mede armies were able to invade Nineveh, then the largest city in the world. “Now we have a historical and environmental dynamic between north and south and between rain-fed agriculture and irrigation-fed agriculture through which we can understand the historical process of how the Babylonians were able to defeat the Assyrians,” said Weiss.
This pattern lines up with historical records of major collapses in other ancient societies, such as the Mayan and Khmer Empires. In these instances, too, corresponding paleoclimate records show agrarian societies flourishing during times of optimal climate and declining in times of drought.
“Agrarian societies are very vulnerable to drought events,” said Colin Kelley, a climate scientist at the Center for Climate and Security in Washington, D.C., and at Columbia University in New York City who was not involved in the new study. “It’s not hard to draw a clear line between food and water security and political unrest.”
Relevance to Modern Drought Cycles
The severity of the Assyrian megadrought also helps add some perspective on modern drought cycles in the Middle and Near East, Kelley said. “This study is really valuable for putting what’s happening today in this region in proper context. The past shows us what’s possible: How dry can it get [and] for how long?”
Over the past 100 years, the Middle East has experienced at least four severe multiyear droughts. “These seem to be happening with greater frequency and severity, which is in line with what we expect with climate change: Dry places are getting drier,” Kelley said. “How this contributes to political unrest in this region is very complicated, but it’s clear that climate change and drought are major factors that should not be underestimated, in the past or in the future.”
The new study was published in Science Advances in November 2019.