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.

 
 
 
 

“Every twitch, breath or thought necessitates a contactless tap”: on the rise of the chain conffeeshop as public space

Mmmm caffeine. Image: Getty.

If you visit Granary Square in Kings Cross or the more recent neighbouring development, Coal Drops Yard, you will find all the makings of a public space: office-workers munching on their lunch-break sandwiches, exuberant toddlers dancing in fountains and the expected spread of tourists.

But the reality is positively Truman Show-esque. These are just a couple examples of privately owned public spaces, or “POPS”,  which – in spite of their deceptively endearing name – are insidiously changing our city’s landscape right beneath us.

The fear is that it is often difficult to know when you are in one, and what that means for your rights. But as well as those places the private sector pretends to be public space, the inverse is equally common, and somewhat less discussed. Often citizens, use clearly private amenities like they are public. And this is never more prevalent than in the case of big-chain coffeeshops.

It goes without saying that London is expensive: often it feels like every twitch, breath or thought necessitates a contactless tap. This is where Starbucks, Pret and Costa come in. Many of us find an alternative in freeloading off their services: a place to sit, free wifi when your data is low, or an easily accessible toilet when you are about in the city. It feels like a passive-aggressive middle-finger to the hole in my pocket, only made possible by the sheer size of these companies, which allows us to go about unnoticed. Like a feature on a trail map, it’s not just that they function as public spaces, but are almost universally recognised as such, peppering our cityscapes like churches or parks.

Shouldn’t these services really be provided by the council, you may cry? Well ideally, yes – but also no, as they are not under legal obligation to do so and in an era of austerity politics, what do you really expect? UK-wide, there has been a 13 per cent drop in the number of public toilets between 2010 and 2018; the London boroughs of Wandsworth and Bromley no longer offer any public conveniences.  


For the vast majority of us, though, this will be at most a nuisance, as it is not so much a matter of if but rather when we will have access to the amenities we need. Architectural historian Ian Borden has made the point that we are free citizens in so far as we shop or work. Call it urban hell or retail heaven, but the fact is that most of us do regularly both of these things, and will cope without public spaces on a day to day. But what about those people who don’t?

It is worth asking exactly what public spaces are meant to be. Supposedly they are inclusive areas that are free and accessible to all. They should be a place you want to be, when you have nowhere else to be. A space for relaxation, to build a community or even to be alone.

So, there's an issue: it's that big-chain cafes rarely meet this criterion. Their recent implementation of codes on bathroom doors is a gentle reminder that not all are welcome, only those that can pay or at least, look as if they could. Employees are then given the power to decide who can freeload and who to turn away. 

This is all too familiar, akin to the hostile architecture implemented in many of our London boroughs. From armrests on benches to spikes on windowsills, a message is sent that you are welcome, just so long as you don’t need to be there. This amounts to nothing less than social exclusion and segregation, and it is homeless people that end up caught in this crossfire.

Between the ‘POPS’ and the coffee shops, we are squeezed further by an ever-growing private sector and a public sector in decline. Gentrification is not just about flat-whites, elaborate facial hair and fixed-gear bikes: it’s also about privatisation and monopolies. Just because something swims like a duck and quacks like a duck that doesn’t mean it is a duck. The same can be said of our public spaces.