Lessons from the Climate-Change Induced Collapse of Angkor Wat

Note: The following is a guest post by Prof. Rob Dunn and friends.

In the context of worries about apocalyptic futures, history and prehistory can play a useful role in framing the ways in which societies deal with major environmental changes. An often mentioned example of such a response is the “collapse” of the society associated with the area of Greater Angkor and the temple of Angkor Wat in the region that is now Cambodia. In the simple telling, climate changed and the society of Greater Angkor couldn’t cope. Collapse followed. But as should be clear in the context of our own current crises (for example, COVID-19) and chronic crises (for example, climate change), the unfolding of major social change is invariably more complex. 

I (RRD) wanted to better understand that complexity and so sat down virtually with Alison Carter (AC), an assistant professor in the Department of Anthropology at the University of Oregon, Miriam T. Stark (MTS), a professor in the Department of Anthropology at the University of Hawaii, Manoa, and Dan Penny (DP), an associate professor at the University of Sydney focusing on environmental history. Carter, Stark and Penny work together as part of the Greater Angkor Project, an effort dedicated to using the tools of many different disciplines to make sense of Greater Angkor’s past. 

RRD: Can you describe what Angkor Wat would have looked like at its peak (however you want to define “peak”)?

A recreation of Angkor Wat by Bruno Levy.

AC: Angkor Wat was one temple within the civic-ceremonial center (kind of like the downtown) of the urban Angkorian complex that we call Greater Angkor. Angkor Wat was built in the early 12th century during the reign of King Suryavarman II. 

RRD: OK, so just to be clear. I asked the wrong question (sorry). I guess what I really meant here was to ask what Angkor Wat and surrounding Greater Angkor would have looked like.

AC: It would have been a bustling place. Constructing this temple itself was a massive undertaking – the temple complex covered nearly 2 square kilometers. However, our Lidar survey* data indicate that a much larger area around the temple was modified, including an area to the east of the moat that includes a mound and pond grid system that seems to be an occupation area and a series of square spirals to the south of the temple. 

*A laser-based approach to mapping, in this case mapping underground structures.

MTS adds: We think the temple might have been plastered, and that the lotus spires could have been covered in gold leaf. A visitor to Angkor in the late 13th century, Zhou Daguan, describes temples being covered in gold leaf. 

RRD: And work by members of the Greater Angkor Project have recently shown that all of this was superimposed on earlier constructions? 

AC: Yes, some of our excavations as well as a Ground Penetrating Radar survey by Till Sonnemann and colleagues suggest that the landscape beneath Angkor Wat was not empty, although it doesn’t seem to have been heavily occupied either. Burials dating to about 3,000 years ago were found in the area of the West Baray (a large water storage tank), so people have been living in the area that would become Angkor for a long time! 

Overview from Sonneman and colleagues of the location of the very ancient buried towers (yellow, at left) of Angkor Wat relative to the slightly less ancient temple (tan/golden, at right) of Angkor Wat (built in the mid-twelfth century CE).
Overview from Sonneman and colleagues of the location of the very ancient buried towers (yellow, at left) of Angkor Wat relative to the slightly less ancient temple (tan/golden, at right) of Angkor Wat (built in the mid-twelfth century CE).

While Angkorian Khmers built Angkor Wat,  people were clearing ground, planning out the grid for the temple complex and surrounding mounds, bringing in stone, dirt, and sand for the temple construction, and carving the decorations throughout the area.  

RRD: So the temple was really an expansion and reworking of what was there before. 

AC: Not exactly. In fact, Miriam Stark would say that Angkor Wat’s size and construction requirements were a radical new experiment in state power.  We’re not quite sure what was there before and to get an accurate idea would need more excavation. Ground Penetrating Radar (GPR) survey shows that there might have been a smaller temple near what would become Angkor Wat and our excavations suggest some kind of activity (i.e. we don’t find sterile soil) prior to Angkor Wat’s construction. The people living here do seem to have been massively re-working the landscape. Once Angkor Wat was completed, we believe  that occupation mounds, with homes, surrounded the temple itself. We’re not sure who these people were, but suspect that they likely worked at the temple. Inscriptions describe many different types of people who worked at a temple to keep it running, from ritual specialists and temple dancers, to people who did more mundane jobs.  Hindu temples were busy places, with near-continuous ritual activities within the Angkor Wat temple; some days each month and year had even larger and more elaborate  public celebrations.

I’m not sure if you’re familiar with the Virtual Angkor Project out of Monash University. The lab there headed by Tom Chandler (son of David Chandler, the respected historian of Cambodia) has been doing amazing CGI reconstructions of Angkor based on written accounts and archaeological data. Some of it is still hypothetical, but it’s a great entry point to imagining what life was like.

RRD: Wow! How amazing. 

RRD: And so the area of Greater Angkor has been occupied for at least three thousand years and the Angkor Wat temple was built in the middle of the 12th century. When did the empire’s collapse begin? What were the key factors that precipitated the collapse?

“Death of Angkor” by Maurice Fievet (1960).
“Death of Angkor” by Maurice Fievet (1960).

AC: First I think you have to define what you mean by collapse, because it can be a loaded term. I think a lot of people envision violent mayhem, destruction, and area abandonment. This did not happen at Angkor. Thai chronicles describe Angkor having been sacked in 1431 and these events were colorfully illustrated by Maurice Fievet in National Geographic in 1960, but we lack clear archaeological evidence for widespread violence or destruction at Angkor. We think, instead, that population decline and socio-political and cultural transformations took place slowly, beginning in the 14th century CE.

RRD: Well, let me re-ask the question again. What are the key factors that precipitated the decline?

AC: We see a convergence of several factors.  Firstly, environmental studies illustrate region-wide monsoon variability, and 14th and 15th century Angkor experienced some periods of severe drought; heavy monsoons (and possibly flooding) followed each drought event.  This did really seem to stress the water management network at Angkor and might have caused a breakdown of parts of this infrastructure.

RRD: So it was too wet, then too dry. Too wet, then too dry.

AC: Yes. However, recent work by Dan Penny and colleagues have complicated this somewhat. They looked more closely at the moat around the walled precinct of Angkor Thom (essentially a walled neighborhood within the urban core of Angkor) and found evidence that Khmer no longer maintained their city moat by the 14th century, which might be evidence that people had begun to move out of Angkor already by the early 14th century. Essentially people were leaving this part of the city before the water management infrastructure failed and this slow demographic decline may have contributed to the collapse of the water network because people weren’t there to make the repairs. It’s an interesting hypothesis that needs to be tested elsewhere around Angkor.

RRD: So in Penny’s model, civic decline preceded the climate change and may then have been exacerbated by climate change (and the failure to invest in the infrastructure required to deal with it)? Sounds familiar.

AC: Perhaps. From his work it does seem like people in that particular part of the city decided not to keep investing in this particular infrastructure. 

AC: What other factors might have caused people to leave Angkor? Tension with the Thai kingdom of Ayutthaya is certainly a push factor*. However, there were also pull factors**, such as increasing maritime trade with China; socio-political centers closer to Phnom Penh were better able to take advantage of this maritime trade. Martin Polkinghorne and colleagues have been doing some interesting work on these Post-Angkorian capitals

*A factor that would “push” them to leave the site.
**A factor that would “pull” them towards other sites.

RRD: And so people might have moved to other cities/capitals because business was better, so to speak?

AC: Yes, much like today. Cambodia has had long-standing business interests with China.

AC: There were also some socio-political and ideological changes taking place in the 14th century that disrupted pre-existing power-structures: primarily the rising influence of a type of Buddhism called Theravada Buddhism. This seems to have changed ideas about how power was organized and expressed; we no longer see stone temples and inscriptions in stone for example. Elites who were previously affiliated with the Hindu and Mahayana Buddhist temples and their economies would have been left behind or have had to adapt to this new system.

RRD: It is amazing how complex it can be to understand cause and effect in a society even as relatively recently as that associated with Greater Angkor.

RRD: Did anyone benefit from the decline? 

AC: We haven’t done enough archaeological work to see how these changes were affecting non-elite people yet. It’s possible, some were able to carry on with life with minimal changes. Other people might have had to move or transform their livelihoods. Surveys by researchers with the Greater Angkor Project and other colleagues have demonstrated that people were still living in parts of the metropolitan area surrounding Angkor’s urban core (where all the temples were) in the 15-17th centuries (In Europe, this roughly corresponds with the time stretching from the renaissance to the enlightenment). So while some temples in the urban core might have been abandoned, other parts of the landscape were not. I think the response was diverse and we’ll need a wider dataset from across the Angkorian landscape to know more. Certainly elite people had the resources and flexibility to make decisions about their lives that poorer people did not, which is true today too.

RRD: Do you see any parallels between how the wealthy are responding to COVID and how the wealthy might have responded to decline in Greater Angkor?

AC: I don’t have a good response for this question. I think similarities might be oversimplifying both situations.

RRD: Well, I guess I just mean to add emphasis to your point above, namely that “elite people had resources and flexibility to make decisions about their lives that poorer people did not.” That statement also seems to characterize our current crisis well.

AC: Yes, I would say that has been true throughout human history.

RRD: As the decline was occurring, how were the species in the urban areas of Greater Angkor changing? Was there a point at which species associated with humans began to become less common or even disappeared? What about rats? Evidence of crops? Household pests?

AC: Faunal remains are rarely preserved in archaeological contexts at Angkor. Partially, I think, due to soil preservation conditions, partially because few residential areas (where faunal remains might be found) have been excavated, and those residential areas that have been excavated have seemingly been kept fairly clean by residents. However, more work has been done on the environment and plants. For this I defer to my colleague Dan Penny.

DP: The faunal response to Angkor’s transformation is poorly documented, in part because the preservation conditions make direct recovery problematic.  The floral response is better understood due to the extensive palaeobotanical work carried out there over two decades, and these patterns may point to broader patterns of ecological change.  We know from large city-enclosures like Angkor Thom that the intensity of occupation began to decrease quite early, from the turn of the 14th century, but that the tail of that decline was very long – at Angkor Thom it may have dragged on for three or four hundred years.  The landscape was clearly peopled, and Angkor’s urban epicenter revert to an Edenic wilderness.

RRD: How closely does the initial decline at Angkor Wat and in Greater Angkor and then subsequent periods of re-use match up with changes in climate? 

AC:  Our work at Angkor Wat is showing that there was changing use of the temple over time. This is really intriguing to me  and I’d really like to do more work there to get a better handle on it. As we wrote in our PNAS article and this piece I (Alison) wrote in The Conversation, we have this funny break in our radiocarbon dates at Angkor Wat and it covers the period when there are a lot of changes happening (described above). It would be great to refine these dates further, maybe we could point to a more specific cause and effect between events taking place at Angkor and changing use of the temple and enclosure space at Angkor Wat. However, I think these things are usually more complicated than a single causal factor, so I suspect that there were many influences. 

RRD: I’m fascinated by the mound and pond agriculture and living structure that your work has uncovered (it reminds me of similar systems in the Bolivian Amazon). Superficially, this seems like a system that might actually buffer some kinds of climatic change well (the ponds pool water that can be used later and also store aquatic food sources, for instance). Is that a reasonable supposition? Was Greater Angkor’s surrounding population well situated with regard to modest climate variation and seasonality?

SE Asian monsoon patters (NOAA)
SE Asian monsoon patters (NOAA)

AC: The monsoon climate in Southeast Asia is seasonally variable, and people across mainland and island southeast Asia were adapting to this seasonality from an early date.  In mainland Southeast Asia there are parts of the year where there is too much water (rainy season) and other parts of the year where there is not enough water (dry season). People are used to this annual cycle and have always planned around this seasonal variability. In Cambodia, the settlement pattern of mounds or clusters of mounds in association with water storage features like ponds goes back quite far – to the first millennium CE and possibly earlier (see Miriam Stark’s work in the Lower Mekong Delta). Mounds would be elevated areas where people are living and the ponds would be places to collect and store water for all manner of use in daily life activities. So yes, it seems that people have had long-standing adaptations to this kind seasonality and the mound-pond habitation pattern is one kind of adaptation.

RRD: Were there other ways that their life ways buffered change? Did they have centralized food storage? Do we know if wealth was repartitioned during hard times?

AC: We don’t have evidence for centralized food storage and Southeast Asian cultigens (agricultural plants) outside of rice don’t really lend themselves to the kind of food storage seen in parts of the other world (like corn and tubers). Prahok, the famous Cambodian fermented fish paste, might have been one way to preserve fish, but we don’t have direct evidence for it archaeologically yet. I think people might have been doing things at a household level, like keeping house gardens, to help buffer potential food shortages. These are interesting questions that need further archaeological investigation! 

I have two sets of colleagues who have looked at changes taking place earlier in Angkor’s timeline that show some transformations in land-holdings that are quite intriguing and I wonder how these earlier transformations might have affected people during the 14th century. One set of colleagues, Eileen and Terry Lustig looked at Khmer and Sanskrit inscriptions that are often associated with temples, and another, Sarah Klassen, along with Damian Evans, looked at top-down and bottom-up water management strategies. There is a nice summary of this work here and I think it is relevant to your question.

RRD: Is there any evidence of what might look like (at least in retrospect) adaptive management. Were changes being made through time that look like reasonable ways of coping with new stresses? 

AC: Yes, we can see changes to the water management network through time that reflect changing landscape use and later seem to be related to the climatic changes. 

Miriam Stark (MS) adds: Southeast Asian agrarian systems are built with this in mind. Delvert (1961) reports on Khmer farmers in the mid 20th century who used more than a dozen varieties of rice regularly to maximize yield. Not only did they practice rainfed and floating and recession techniques, but they used rice varieties with different maturation times on micro-topographically distinct levels of rice fields whose inundation period (from annual flooding) varied by a few weeks. The water management stuff is great but primarily focused on protecting urban Angkor. I think agrarian strategies are equally important in the long run. 

RRD: The climate economist Solomon Hsiang has written about Greater Angkor (and other sites) that “we see it again and again, things are going great until a major climate pulse and then they collapse. They don’t see it coming. Or they see it and can’t imagine how to respond.” In some ways, this sentiment seems resonant in our current COVID time. Is it accurate in the context of Greater Angkor? 

AC: Not really. The Angkorian people certainly couldn’t have predicted the decades-long monsoon/drought cycle that took place. They didn’t cause these monsoon events and could only react to them. We can see this in the adaptations they made to the water management system (like the construction of the Siem Reap canal described by Fletcher here). The COVID-19 situation in the US is due in large part to failures in government leadership ignoring science, scientists, and public health officials whose warnings and advice is going unheeded. I would say the poor COVID-19 response in the US and the decline of the Angkorian civilization are not comparable at all.

RRD: So the point you are drawing out here is that our time is different in that we see the problems (be they COVID-19’s spread or climate change) coming and despite seeing them coming are failing to deal with them, whereas the people of Greater Angkor did not see the changes in climate. I guess that makes our response more foolish at the scale of our global and national-level responses. But from the perspective of individual towns/regions, we (to me) seem to be a great deal like the people of Greater Angkor in that while long-term climate trends (at least with regard to temperature and mean precipitation) are relatively predictable, next year’s weather is not, especially when it comes to monsoons and droughts. 

MS: As a social scientist, I’d argue that ultimately social factors drive these sorts of collapses in the past as well as today. We can’t usually reconstruct the social histories of premodern collapse, but today we can see how decisions by political leaders are responsible for the severity of COVID globally: and collective social response. They should have taken action, and we should too: but both parties lack the will, and so we are in crisis. Going back to your question, “can’t imagine how to respond” is not how I’d describe it. Instead I’d focus on limits on organizational systems to respond to change: so it’s a systemic or structural issue as much as a social one.The Angkorian political structure–which required ‘buy-in’ by hundreds (or maybe thousands) of people–buckled under in the face of intense climatic and structural pressure. Things were falling apart; rulers were ineffective at trouble-shooting; people were tired of trying to make it work; and perhaps–like so many other places in Southeast Asia–Angkorian kings ultimately lost their mandate to rule. In Khmer, the term for sanctioned power is “omnaich,” and people decided they were not willing to be subjects.  

RRD: So at the time of the crisis, the kings no longer had “omnaich,” they no longer had sanctioned power.

MS: Chinese historians use the term “mandate of heaven” to discuss something similar, and Southeast Asian historians talk about similar terms across the region. Ben Anderson (1972) used the Javanese term wahyu in his influential discussion of the idea of power. Anthropologists like Chris Boehm (1993) pointed out, long ago, that rulers need consent of the ruled — whether these are chiefs or kings — and without it the subjects walk away. *

*Miriam discusses the Angkorian case in her 2019 paper on “Universal Rule and Precarious Empire.”

RRD: Angkor Wat is, in some ways, so very recent. Why don’t we already know more about its history and ecology? Why isn’t there more in the actual historic records? 

AC: This is a Euro/Western perspective–the civilization of Angkor was well-known across Asia and there’s quite a bit about it in the records! The only writings from the Angkor period (9-15th centuries) that have been preserved were written in stone and these inscriptions had a specific agenda/template for what they were writing about. There may have been more diverse writings on palm-leaf manuscripts that have not survived. There are numerous written chronicles from the period we call Post-Angkor (aka Early Modern Period) that detail activities of the royal courts of Southeast Asia.  Even after the decline of Angkor as a capital, people returned to this site and visited specific temples, especially Angkor Wat. There are Portuguese and Spanish sources recording information on Cambodia and Angkor from the 16th century. There is graffiti at Angkor Wat from visitors across Asia; a Japanese visitor to Angkor drew one of the first maps of Angkor Wat in the 17th century. There was an Arabic stele found at the temple site of Phnom Bakheng also from the 17th century.  Angkor was not unknown.

RRD: OK, but at the same time you are still making new discoveries about very fundamental aspects of the Greater Angkor society. Where people lived, how many people lived there, etc…. Presumably that we don’t already know those things isn’t just a Western bias.

AC: This is true to an extent, but I don’t want to give an impression that Angkor was a mysterious, unknown place! Henri Mouhot is largely credited with “discovering” Angkor, although he himself never made this claim and acknowledged earlier European visitors. However, the narrative of discovery served the French colonial agenda–if Cambodians had forgotten about their “civilized” past then it justified the French colonial mission in Indochina (quite a few authors have written about this, including Penny Edwards and David Chandler).

RRD: So is it fair to say that more was known about some aspects of Greater Angkor in the sixteen and seventeen hundreds than is known today? 

AC: To some extent. Cambodia is a special case because the Khmer Rouge era wiped out so much of the population that a lot of knowledge was lost. 

AC: As for the ecology of Angkor (this might be more detail than you want): an interest in an archaeological study of the environment grew out of what was called “the processual movement” in archaeology (largely in the US) in the mid-20th century and expanded with the development of specific field and lab methods aimed at addressing questions regarding the environment and ecology. This kind of thinking hadn’t reached French-influenced Cambodian archaeology before the extensive US bombing and Khmer Rouge period, which stopped all archaeological research (and intellectual pursuits) in Cambodia from the early 1970s-1990s.  It took a few years for the archaeology program in Cambodia to get re-started in the 1990s and early 2000s. Much of the environmental work has been undertaken since then and we’ve learned a lot about what is happening at Angkor in a relatively short period of time! I think it’s a great success story actually; the knowledge about Angkor has grown exponentially in the last 20 years and more recently a lot of this has been driven by or in collaboration with Cambodian scholars. See also this recent work on community archaeology in Cambodia by Piphal Heng and colleagues. 

RRD: Thank you Alison, Miriam and Dan for your time and thoughtful answers. Do you want to close by saying a little about what you are most excited about, moving forward, in the study of Greater Angkor (or in your own work more generally)? 

AC: There is still so much to learn about Angkor! Right now, my colleagues, including Miriam Stark, Piphal Heng, and Rachna Chhay and I, in collaboration with the APSARA Authority and Cambodia’s Ministry of Culture and Fine Arts, are trying to understand the city at a finer-grained scale- from households to neighborhoods and districts within the broader settlement complex. A group of us led by Sarah Klassen is also trying to understand how Angkor grew over time, including a revised population estimate. And Miriam Stark and I have also begun a project looking at what life was like in Angkor’s provinces.  We’re just one group among many working on the Angkor civilization. It’s like a puzzle, we’re all putting the pieces together and a clearer and clearer picture of Angkorian life is emerging. 

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