This is how Gupta and Chola empires fell—climate catastrophe, pandemic, migration

Indians created fragile systems that collapsed under environmental pressure. The best example of this is the Indus Valley Civilisation.

The Brihadeeshwara temple at Thanjavur, which according to Chola inscriptions was endowed with tonnes of gold and royal insignia | Wikimedia Commons

The history of Asian empires warns us: climate disasters wait for no one. The most populous city in the world was laid low by the monsoon; the most advanced Bronze Age civilisation was emptied by drying weather; and climate disasters played into the fall of both North Indian and South Indian empires.

The fall of Asia’s greatest city

The largest Hindu temple in the world, Angkor Wat, is reflected in the waters of a man-made lake. Around it is a vast abandoned city: Angkor, Cambodia. In the 12th–13th  centuries CE, Angkor was perhaps the largest city in the world—larger even than Indian cities at the time. Extending nearly 1,000 square kilometres, the region was home to as many as a million people. In comparison, the largest pre-modern Indian city, Vijayanagara, had perhaps 4,00,000 inhabitants.

To feed so many mouths, the people of Angkor built hydraulic works over the course of 300 years, gradually expanding and connecting smaller systems. The end result was a stupendous water collection and distribution network, extending over nearly 3,000 square kilometres. An extensive multidisciplinary study found that this consisted of three main zones. Rivers flowing from the Kulen mountains in the north were diverted in the first, uppermost zone. The middle zone aggregated this water in massive tanks in the city, with a total capacity of up to 1.2 billion litres. Many of these tanks surrounded temples or were adjacent to them. This enormous body of water was slowly released for rice cultivation, tiding the city through Cambodia’s long summers. Excess water was collected by a drainage zone and delivered to the Tonlé Sap Lake—the largest freshwater body in Southeast Asia. 

But Angkor was hit by a series of climate disasters in the 14th century, seriously weakening its water systems. Part of the flaw lay in the system itself. It was not a single united plan, but a series of expansions and corrections to smaller plans—all with their own issues. 

Hydrologist Matti Kummu writes that in the upper hydraulic zone, Angkor’s engineers built straight collection channels, breaking apart the catchment area of the Puok river, and cutting the water across the natural slope. Water flows much faster in straight channels, eroding the banks and depositing massive quantities of silt. But much bigger problems were two droughts that lasted for decades in the 14th century. Engineers were forced to make expensive modifications to the system. But then, right after the drought, torrential monsoons overloaded the fragile water system, destroying huge sections and forcing the city’s kings and masses to move elsewhere.

Climate and Indian Empires

The climate wasn’t the only factor in the collapse of Asian civilisations. In his new book, Pox Romana: The Plague that Shook the Roman World, historian Colin Elliott studied the Antonine Plague—a mysterious disease that swept through much of Europe in the 2nd century CE. The pandemic, he finds, benefited from Rome’s unhygienic urban centres, its poor health infrastructure, and its excellent road connectivity. It worsened existing problems in the empire’s fragile economic and health supply systems. And it almost certainly came from the east, via Iran, and possibly from India. 

Intriguingly, Elliott points out that at the same time, Hariti—a Buddhist goddess associated with disease and childbirth—appeared frequently in the art of the Kushan Empire in northern India. It’s possible these were linked, though we need more evidence to be sure.

Unlike Angkor and Rome, India hasn’t been able to fund multidisciplinary studies on pre-modern disease and the environment. And so when Indian writers talk about our relationship with the environment, we tend to congratulate ourselves that our ancestors lived in perfect harmony with nature. They usually arrive at that conclusion by massively over-interpreting texts, with no other data. (Just Google “ancient India environment” and you’ll see what I mean). But Indians could (and did) engineer their environments, and created fragile systems that collapsed under environmental pressure. The best-attested example of this is the Indus Valley Civilisation, which, as my colleague Disha Ahluwalia writes, was de-urbanised by increasingly arid climates.

Environmental stress also played into the collapse of the Chola Empire in South India. As historian R Tirumalai writes in Land Grants and Agrarian Reactions in Chola and Pandya Times, from the 12th century onwards, there were repeated floods in the Kaveri and Cheyyar river systems. The floods were bad enough, but landlords disastrously mismanaged the crisis, insisting that cultivators pay tax anyway. Others used the crisis as an opportunity to buy land for cheap. This short-sighted speculation made many rich but left others destitute. By the late 12th and early 13th centuries, inscriptions reveal that people were selling themselves into slavery. The natural crisis was worsened by human action.

There are other tantalising examples. In The Fate of Rome: Climate, Disease and the End of an Empire, historian Kyle Harper studied ice cores and tree rings. It turns out that in 536 CE, volcanic eruptions led to catastrophic global cooling. Documents from all over the world describe a darkening of the skies, longer winters, and failing harvests. Around the same time in India, the Huns from Central Asia were pressing into the Gangetic Plains, leading to the collapse of the Gupta Empire. These events were almost certainly interconnected. But through what mechanisms? At least we know what cooling climates led to in the Mediterranean. Failing harvests stressed revenue systems. Reduced immunity caused pandemics. Migration and wars wiped out trade.

Learn from the past

The point of all of this isn’t to terrify, but to point out that we must learn from the past. Yes, climate change is coming. But each example teaches us a different lesson. Angkor shows us that we need to build and maintain resilient systems, and accurate climate models that are prepared for catastrophe. The Romans and Kushans remind us to take public health seriously, and not to leave everything to the gods. The Harappans suggest that smaller cities might be better adapted to changing climate. The Chola aristocracy is a warning that inequalities will worsen. And the Gupta empire’s collapse hints at what’s coming in future decades: failing harvests, migrations, pandemics, and decreasing trade. 

We can’t keep going the way we are and pretend everything will be fine. The least we can do is learn from the triumphs and struggles of our ancestors.

Anirudh Kanisetti is a public historian. He is the author of Lords of the Deccan, a new history of medieval South India, and hosts the Echoes of India and Yuddha podcasts. He tweets @AKanisetti. Views are personal.

This article is a part of the ‘Thinking Medieval‘ series that takes a deep dive into India’s medieval culture, politics, and history.

(Edited by Ratan Priya)