The collapse of the ancient Cambodian city of Angkor holds lessons for urban resilience today

The ruins of the Ta Phrom temple, Angkor. Image: Diego Delso/Wikimedia Commons.

A series of floods that hit the ancient city of Angkor would have overwhelmed and destroyed its vast water network, according to a new study that provides an explanation for the downfall of the world’s biggest pre-industrial city.

Our research, published in Science Advances, explains how the damage to this vital network would have triggered a series of “cascading failures” that ultimately toppled the entire city. And it holds lessons for today’s cities about the danger posed when crucial infrastructure is overwhelmed.

Angkor, in modern-day Cambodia, was founded in AD802 and abandoned during the 15th century. Its demise coincided with a period of highly variable rainfall in the late 14th and early 15th centuries, with prolonged droughts and extremely wet years.

We know Angkor’s water distribution network was heavily damaged by flooding during that period. But we didn’t have an explanation of how this triggered the city’s eventual collapse and abandonment.

Flooding fate

Angkor is an unusual archaeological site because the remains of the city can still be seen on the ground and, particularly, from the air. It is thus possible to map precisely the constructed features that made up its urban fabric and, from this, to interpret the function and flow of the living city.

We used existing archaeological maps of Angkor to chart the city’s water distribution network, which was made up of hundreds of excavated canals and embankments, temple moats, reservoirs, natural river channels, and other features. This sprawling network, covering more than 1,000km2, provided both irrigation and flood defence.

We then used a computer model to simulate the effects of flooding, such as would have occurred during huge monsoonal rains, to see how the system would have coped with the biggest deluges.

We found that large floods would have been channelled into just a few major pathways, which would have suffered significant erosion as a result. Other parts of the network, meanwhile, would have had less water flow and would have begun to fill up with sediment.

The resulting feedback loop would have caused damage to cascade through the network, ultimately fragmenting Angkor’s water infrastructure.

A watery end. Image: Alcyon/Wikimedia Commons.

There are two main messages from our research. First, it demonstrates how climatic variability in the 14th and 15th centuries could have triggered the demise of the city.

Second, it shows how Angkor’s fate resonates with today’s concerns about the resilience of our own urban infrastructure – not just to extreme weather (although that is important), but also to other potentially damaging events such as terrorism.

Angkor was once the largest city on Earth. But its huge growth made it unworkable, unwieldy, and ultimately irreparable. Its critical urban infrastructure was both complex and interdependent, meaning that a seemingly small disruption (such as a flood) could fracture the entire network and bring down an entire city.

Ancient Angkor, it seems, experienced the same challenges as modern urban networks. As we move further into a period characterised by extreme weather events, the resilience of our urban infrastructure will be tested.


As cities grow, their infrastructure becomes more complex. Eventually, networks such as roads, water infrastructure or electricity grids reach a critical state that is neither predicted nor designed by those that operate them. In these networks, small errors or outages in one part of the network can quickly propagate to become a much larger failure. One example would be an electrical fault that triggers a wide-scale blackout.

Government agencies around the world have developed or are developing strategies to deal with threats to critical infrastructure, including from terrorism, natural disasters and, increasingly, extreme weather events related to climate change. Resilience can be built into infrastructural networks by increasing redundancy (or alternative flow paths) and emphasising modularity, so that cascading failures, if they occur, can be localised while maintaining the function of the wider network.

Our research on the demise of Angkor’s infrastructure sounds a warning from history about the dangers of the complex urban environments in which most humans now live, and the urgent need to prepare for a more variable future.

The Conversation

Dan Penny, Associate Professor, University of Sydney.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

 
 
 
 

Could twin towns bring Britain back together?

An unlikely pair. Image: Wikimedia Commons.

Twin towns: an irrelevant novelty to most of us, a peculiar name on a village’s welcome sign. But could linking one British town to another – a domestic reinterpretation of this long-standing European practice – help bring Britain back together in a time of national crisis?

Born in the aftermath of World War II, town twinning aimed to foster cooperation and solidarity across Europe. Communities entered formal alliances, nurturing friendships and shared histories. Coventry forged links with Dresden and Volgograd, then Stalingrad, marking the devastation faced by their citizens during the war.

The democratisation of Greece, Spain and Portugal during the 1970s led to a new wave of twin towns across Europe, as did the fall of the Soviet Union a decade later. Since its inception, the focus of town twinning has been on uniting people through relationships. It is a testament to the initiative’s success that many of these remain to this day; Coventry recently enjoyed a performance at the city’s cathedral by Volgograd’s children’s choir.

While European relations have improved since the 1940s, unity at home has received less attention. As a result, Britain is riven with deep economic, political, educational and cultural divides. These fault lines are increasingly determined by geography, with a growing gap between our big metropolitan cities and almost everywhere else.

In comparison to other European countries, we face staggering levels of regional inequality; six of the ten poorest regions in northern Europe can been found in the UK. As outlined by Alan Milburn, the government’s former social mobility tsar, “the country seems to be in the grip of a self-reinforcing spiral of ever-growing division. That takes a spatial form, not just a social one.”

These divisions are poisoning our body politic. As Adam Smith argued in The Theory of Moral Sentiments, putting yourself in someone else's shoes is vital for developing a moral compass; in doing so "we conceive ourselves enduring all the same torments, we enter as it were into his body, and become in some measure the same person with him..." But this is difficult when we have little interaction or experience of those with opposing views.

This is increasingly likely in geographically polarised Britain, with the places we live dominated by people who think alike. Our political leaders must commit time and energy to bridging these divides, just as the leaders of Europe did in the aftermath of the Second World War. By forging links between different parts of the country, a new era of domestic town twinning would do just that.


School exchanges between sister towns would offer an opportunity for children to be exposed to places, people and perspectives very different to their own. This would allow future generations to see things from an alternative and opposing perspective. It may also embed from a young age an awareness of the diversity of experiences seen by people across our highly unequal country.

MPs would be encouraged to spend time in their constituency’s sister town. First-hand exposure to voters in a very different part of the country would surely soften the views of even the most entrenched parliamentarian, making for a more civil debate in the Commons. Imagine the good this would do for Parliament today, with Brexit gridlocked because of the unwillingness of MPs to compromise.

In 2016 the Carnegie UK Trust launched its Twin Towns UK programme, a pilot linking twenty towns across the UK to examine how they might develop together. Emerging benefits include a reduction of insularity and a greater awareness of the bigger picture. Its focus was not on bridging economic divides – towns with similar socioeconomic characteristics were twinned – but initial outcomes from the scheme suggest a broader programme of domestic town twinning could have a powerful impact.

Looking further back, Camden has been twinned with Doncaster since the 1980s, a relationship that unionised Camden Town Hall workers forged in a display of solidarity with striking miners during the 1980s. Funds were raised to feed families of striking workers at the pit and Camden locals even drove north to deliver presents at Christmas. Though the relationship appears less active today, it serves as a powerful reminder of twinning’s capacity to bring people from very different places together.

As we prepare for Brexit it’s imperative that we protect existing twin town relationships with our European partners. This is of vital importance when we know sadly many of these are under threat from austerity and gloriously un-PC mayors. But we should look to breathe new life into these traditions too, where possible. Domestic town twinning would do just that: a step towards bringing Britain back together, just as a continent was reunited after the devastation of war.

Ben Glover is a researcher at the think tank Demos.