Transcription of Damian Evans' & Peter D. Sharrock's lectures "Uncovering the Real Angkor: Early Civilisations Mapped Using Cutting-Edge Technology" (Royal Geographical Society, London, 13 June 2016)

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This is a transcription of the lectures by Damian Evans & Peter D. Sharrock, as conducted during the lecture event entitled "Uncovering the Real Angkor: Early Civilisations Mapped Using Cutting-Edge Technology". That lecture event was organized by the "Global Heritage Fund UK", and proceeded in "The Ondaatje Theatre" of the "Royal Geographical Society" in London, United Kingdom on Monday, 13 June 2016 from 18:30 to 20:30 (BST).

For more meta-information about that past event, cf. its entry on the "Eventbrite" ticketing platform or its entry at SOAS University of London.

Please note that this transcription was not undertaken by any person involved in the organization of the lecture event, nor by any of the persons speaking during the lecture. Instead it was undertaken by an individual, in a not-for-profit attempt to make the scientific lectures available freely for a broader section of mankind after the presentation.

I had wished to also record and distribute the lectures videographically, as well as distribute the PowerPoint slides of the presentations, but when I mailed both speakers in this regard (on & & &, I never received any answer. I also mailed the Global Heritage Fund, to ask for permission for my videographic recording and to obtain the PowerPoint slides, but in return only received the following negative reply from Cathy Giangrande: Dear Mr Verheyen,

I have asked the speakers, and I'm afraid that they both cannot provide your with the PP slides, nor will you be able to record the lecture. Sorry we could not be more helpful.

Thank you.
As far as I am aware, at least 1 or 2 other actors were recording the lecture video-graphically, but only parts of the lectures. Footage of one of the 2 present camera's during parts of the lecture were mixed into a video news report by Al Jazeera, which also interviewed the speakers before the lectures. That video news report can be watched below:
  • 0:21-0:39 | An interview with Peter D. Sharrock before the lectures.
  • 0:40-0:47 | Video footage of Damian Evans' lecture.
Please note that the images presented in this article may differ substantially from the original PowerPoint-slides presented at the lecture. As for Damian Evans' lecture, the pictures which I used are mainly based on another somewhat similar presentation; which was recorded videographically, and was held in the The Siam Society in Bangkok, Thailand on 4 February 2016:
  • Part 1:
  • Part 2:

Introduction by the host, of the Global Heritage Fund

[...] I am thrilled as a trustee of the Global Heritage Fund, to be introducing 2 speakers who’s work has stunningly illuminated the site of Banteay Chhmar and the Angkorean empire more widely.
  • Damian Evans has worked on the archeology of Cambodia since the 1990s, specialising in using remote sensing techniques, and; as I remember; a very powerful motorbike now sold sadly. To uncover and map and analyse archeological landscape features of the country. In 2015 he joined the École française d'Extrême-Orient and is currently the principal investigator of the Cambodian Archaeological LiDAR Initiative, whose remarkable findings he is going to present during his talk today.

  • Peter Sharrock’s vast experience in South-East Asia started as a correspondent for Reuters, covering the American war in Indochina. He began his academic work at a time when landmines abounded and temples changed hands between Khmer Rouge forces and government forces on a daily basis. His work focuses on how we can use the iconography of temples and state iconography to shed light where there is a huge lack of residue material, informing us about the political landscape in Cambodia during the reign of its foremost ruler King Jayavarman VII.

We are; GHF [Global Heritage Fund] is; and we are all lucky to have 2 speakers whose methods differ widely, but whose ends; I think; are shared in the illumination of the Angkorean empire.

A bit about GHF [Global Heritage Fund]: we are a a heritage conservancy that restores World Heritage sites in developing countries. Banteay Chhmar, which is in the impoverished very arid northwest Cambodia is more or less a textbook example of how a Heritage Site that is properly nurtured and managed can provide education, a training and opportunities for local people. And so since 2008, Global Heritage Fund has carried out a series of conservation interventions, training programs, and community-based tourism initiatives, which aims to make the heritage there work for local people, and to fit the site into the wider national heritage infrastructure on which the future of Cambodia relies in many ways. We don’t set up to work alone; we work in partnerships; and we see ourselves as a catalytic organisation: working for a number of years at a site to kick-start public and private funding for conservation as well as sustainable development. To that end I would like to thank our partners and our sponsors, including the Cambodian Ministry of Culture and Fine Arts, the National Authority for the Protection and Management of Angkor and the Region of Siem Reap (which I have always known as APSARA) […] of that rather long acronym […], and the European Research Council, the École française d'Extrême-Orient, the School of Oriental and African Studies [SOAS], the Friends of Khmer Culture International, ABOUTAsia Travel, The C P Charitable Trust, and The Alphabet Foundation.

Please note that we will have time for questions at the end of the 2 speeches, and I would finally like to thank you all for coming, and ask […] the speaker to the stage.


Main speeches

Damian Evans' main speech

Thank you very much [...]. Good evening Your Royal Highness, ladies and gentlemen. I am very pleased to be here this evening to talk to you about some of the latest discoveries at Angkor; and also of places far beyond Angkor as well.

It's obviously quite timely, as you may have seen a lot of quite sensational and mostly correct news reports about this recent work in the media over the weekend. In fact, the RGS [Royal Geographical Society] actually has to bear some of the blame for this, having funded the very first expedition to [...] Angkor in the 1850s by the Frenchman Henri Mouhot, who wrote a series very [...] and romantic accounts: finding an exotic lost civilization consumed by the jungle [...] published by the RGS [Royal Geographical Society] as well, which it seems has kind of set the tone for coverage of Angkor, even today in the digital age.

Anyway though, it really is quite an exciting time to be an archaeologist. And I would say probably the most exciting time since the beginning of aviation really, to be an aerial archaeologist like myself: someone who's job it is to look from above for patterns from the past.

What was seen and what's being reported over the weekend is a particular convergence of emerging technologies, big data, and new ways of looking at the past. And really, what we're starting to do is to take into account the full complexity of the relationship between humans and their environment over extreme large scales of time and space. The work that has taken place in Cambodia since the 1990s, I think in many ways exemplifies the kinds of opportunities and challenges that this approach presents and how they are being addressed both on the ground and from the air. And perhaps nowhere is this more powerfully illustrated than with the application of airborne laser scanning or LiDAR [Light Detection And Ranging] to the landscapes of the Khmer. So, for instance; whereas what we used to have in terms of our view of places like Angkor Wat, was a stone temple surrounded by forests, surrounded by a moat, even further surrounded by forests; now, what we are able to do using LiDAR technology is virtually lift the lid and strip that vegetation from out our view and reveal this very highly structured urban landscape that was previously obscured by vegetation. And so these are the kinds of things that I'll be talking about this evening.

  • Caption: An oblique view of Angkor Wat and its immediate environs. Upper layer: Digital orthophoto mosaic, with elevation derived from the lidar digital surface model at 1-m resolution. Lower layer: extruded lidar digital terrain model, with 0.5-m resolution and 2× vertical exaggeration. Red lines indicate modern linear features including roads and canals.
  • Source: "Uncovering archaeological landscapes at Angkor using LiDAR", in: Proceedings of the National Academy of Sciences of the United States of America [PNAS], 2013.
  • Caption: An orthophotograph of Angkor Wat taken during the LiDAR survey in 2012 (image courtesy of KALC).
  • Source: Published in "Angkor Wat: an introduction", at ResearchGate.
To begin with though, returning to historical scholarship; essentially most of the work that has been done on Angkor over the last 100-150 years has focused very much on the temples.

  • Caption: Buddha Stroll Through Angkor Wat.
  • Photo: Trey Ratcliff.
  • Source: "Stuck In Customs", in: Flickr.
And so we know an awful lot about these structures: about who built them, when, how they were constructed. And the reason why most teams traditionally have been working on those temples, and even today most teams continue to work on the temples is for the very simple reason that they are a mess basically: they look very solid and very sturdy; but in fact, for various reasons there were flaws in their construction, and many were at an extremely bad state of repair in the 19th century. And so that's why almost all of the work is concentrated on those.

  • Caption: Picture taken in the 1940s, showing the collapse of a temple.
  • Scan of photo: upload of user "橘子汁里的鱼", at 穷游网 (
The other main focus has been on the artworks, the artefacts, and the narrative reliefs that are inscribed into the walls of the temples, which has been the focus of intensive study over the last 150 years.

  • Caption: Brahma. Cambodia, province of Cambodge, province de Siem Reap, Phnom Bok, style of Bakheng, end of the 9th - beginning of the 10th century, fin 9ème - début 10ème siècle, sandstone. The Guimet Museum (Musée Guimet) in Paris.
  • Source: photographed and upload of user "Vassil", at Wikipedia.

  • Caption: A narrative bas-relief inside the Bayon, in Siem Reap.
  • Source: "Cambodia Snapshots: Tales on Stone", at the blog on Cambodia called LuiinPenh (before called 'Pinaywifespeaks').
But really our main source of evidence for this period in history ... I remember you of course that the Khmer Empire stretched across much of mainland Southeast Asia at its highest [...] between the 9th and the 15th centuries comes from these inscriptions. This collection of inscriptions that is mostly written in Sanskrit and Old Khmer (the ancestral language of modern Khmer). And the fact that several hundred years of Southeast Asian history revolves around these inscriptions is quite problematic. For one thing they tend to be commissioned by royalty, so they are designed to give a very specific and very particular point of view about what's going on. They don't really tell us about things that are of interest to archaeologists: things going wrong and so on ... There's also relatively few of them, considering the geographic and temporal extent of the Khmer Empire. And they are also quite fragmentary as well. And so it's a real problem in fact that this is essentially the foundation of our understanding of this entire period.

And indeed, what we're left with, beyond these inscriptions, is basically the stone skeleton of the temples themselves. So, if you go to Angkor and you see a temple like this, it's quite difficult to imagine really that had you been there a thousands year ago, that it would have looked radically different. Not like this at all, but adorn with metal and wooden buildings and artifacts. It would have been brightly decorated and painted. And so had you gone to a temple like this a thousand years ago, you would have seen something that in fact looks something much more like that.

  • Caption: These colourful overlays, when seen on top of photographs showing the temples as they appear today, provide the best guess that we have currently as to their original appearance.
  • Photo: Bruno Lévy and Stéphane de Greef.
  • Source: "Angkor: an interactive map of Cambodia's must-see temples", at The Telegraph.
So even the temples themselves were missing a very large part of the picture. The situation is even worse beyond the temples. Essentially, during the Angkor period, houses of stone were reserved for the gods; and everyone else, from the king on down, had to live in buildings made of non-durable material like wood and thatched. Even the king himself had to live in a palace that was made of wood, and which rotted away many many centuries ago. And so this of course is very problematic for archaeologists because our main source of evidence for the cities that surrounded those temples has disappeared. The temples themselves were in fact just a very very small fracture of the overall picture, and yet they are all that remains.

Too bad to the difficulties that we face, of course being in the Hindu-Boeddhist tradition they cremated the death, so we don't even have skeletal remains to work with, in the case of the Khmer civilization.

So what we began to do, as archaeologists, to try and understand the trajectory of the growth of Khmer civilization and the evolution of their cities and lived-in spaces, to try and understand the success of Angkor; is to look at the subsistence: is to look at how they survived in their really quite harsh environment. If you look at this mosaic of rice fields that stretches all across Southeast Asia, you somehow get the impression that it's a very lush and abundant environment. But, in fact, the farmers who cultivated rice in these fields lived a very precarious existence, very much at the mercy of seasonal rainfall variations, variations in annual rainfall. And it's not at all a particularly stable mode of subsistence. There is a very high degree of vulnerability to annual, decadal variations in climate. So, this is something that interests us, obviously; and it's something that needs to be understood and explained if we end to fully understand the reasons for the rise of Angkor.

Unfortunately, up until the 1990s, all we had were these very very simple schematic maps of Angkor. You can see the largest of the temples are marked here in the middle, these large reservoirs and baray above the moat are marked. There was a series of linear features marked on maps: people mostly didn't know if those were canals or roads. And you can see a scatter of apparently disconnected temple sites, scattered across the landscapes. So, very simple schematic maps that don't really tell us a great deal about what's going on in the broader landscape beyond the ceremonial centre and the largest of the temples.

Fortunately, what people began to realize in the 1990s is that using remote sensing technologies, and looking from above, we could see the remnant traces of these vanished wooden cities remaining in the surface of the landscape. So, where people built wooden neighbourhoods, they did so on top of mounds of earth that they heaped up to keep above water during the wet season. They excavated ponds to keep water during the dry season. If we look from above, we can very clearly see that some of those linear features are dams or roadways, whereas others are very obviously canals from the Angkor period as well. Perhaps most importantly of all, we were able to identify a particular kind of archaeological feature which we call a neighbourhood temple. And so we discovered about a 1000 additional temples at Angkor in the last 20-25 years of mapping. But of course we shouldn’t imagine that these are huge stone monuments or anything. In fact, you can be standing right on top of one of these temples, and not even know it. But if you look from above, it has a very specific spatial signature: it has a mound in the middle; the mound is surrounded by a moat; there is always a causeway on the eastern side, which gives the moat that very distinctive horseshoe-shape. And it doesn’t look like much if you go there and if you’re lucky maybe see a few bricks on the ground. But, really it’s kind of the building block of the city that surrounded Angkor. We know, looking at a configuration like that, that a neighbourhood temple stood here, and this was the centre of a community of hundreds of families, of thousands of people. So, what you’re seeing here is really the urban fabric of the Angkor area.

So, my colleague Christophe Pottier from the École française d'Extrême-Orient and I; between the 2 of us; spent about 25 years mapping all of those elements in greater Angkor area. And as a result of that, we have been able to move from these very schematic maps of Angkor to really quite sophisticated maps of the greater Angkor area that show it in all of its complexity. And what we have been able to show is that, essentially, the reason for the success of Angkor: what they did is they harnessed the natural flow of water from this watershed in the mountains to the north here, which in the normal state of affairs would flow down to Cambodia’s great lake; what they have done is they have created an elaborate system of collection to harness that water, to store it in these great reservoirs here, and then create a series of dispersive canals to move that out into the rice fields. So they basically created a system to mitigate flooding, and also to guarantee at least a minimum rice yield during years of poor rainfall. And just to give you an idea of the scale of what was achieved at Angkor, here is one; just one; of the many large reservoirs; this one is the West Baray, this one is 8 kilometres long on its north and south sides and 2 kilometres long on its east and west sides. It’s the biggest one at Angkor, but not by far; there are others that are nearly as big. And so the scale of what was achieved here is tremendous, and really underpinning the rise and the success of Angkor and the Indo-civilization. And also probably sowed the seeds of their demise as well. What we can see is the creation of this water management system, the expansion of the city, posing very serious environmental problems which impacted very very strongly on the water management system which eventually failed. And so it's quite a paradox in some ways that they sowed the seeds of their own demise, even as they rose to they kinds of heights and glory in the 12th to 13th century.

Just to give you an idea of the scale of Angkor, and what was achieved there; which is difficult to get a sense of just from looking at maps; but if you look at a map of greater Angkor, the one that we published in 2007, compared on exactly the same scale to a map of London, you can really appreciate the enormity of what was achieved in this great pre-industrial city, perhaps the largest pre-industrial sub-urban complex in all of human history, at least as far as we know, to this point.

  • Caption: "A new archaeological map of Greater Angkor" compared with the size of greater London. In the bottom map, the red circle has a diameter of 67.5km, which approximately equals the represented width of the top map.
  • Compilation: Vincent Verheyen.
  • Source: For top image: see "A new archaeological map of Greater Angkor" above. For bottom image: Google Static Map Maker (click here to open the image if the bottom image failed to load).
So, the big problem for us; if you look at this map very carefully, is that a lot of these [...] of environmental degradation and decline revolve around there being a huge population in the centre of Angkor, as well as the city expanding into these northern regions, causing large amounts of deforestation and cascading problems of flooding and sedimentation in the centre of the system. As you can see though, in these maps, there doesn't really seem all that much going on up in the north, and the density of features in the centre of Angkor doesn't really seem to be all that great. In fact, that's not because there's nothing going on in those places; that's because you remember we were tracing the remains of this civilization by looking at these very subtle lumps and bumps on the surface of the landscape, this archaeological typography. It doesn't really look like much from the ground, but from the air you can really make sense of it. Of course, where that topography is obscured by trees, we can't create archaeological maps in those areas; or at least: we never used to be able to create archaeological maps in those areas over very wide scales. You could do limited topo-surveys on the ground, but it was time-consuming and dangerous.

The solution to this particular problem has come to us very recently, in the form of a technology called LiDAR, which basically has the ability to see through this vegetation that surrounds Angkor and the central temples of the Angkor complex. LiDAR is just basically a giant laser scanner that's strapped to the side of the helicopter or put in an aircraft.

  • Caption: Three senior monks from the Banteay Chhmar pagoda prepare a ceremony to bless the replacement LiDAR instrument.
  • Source: Damian Evans, "Data Acquisition Passes the Half-Way Mark", in: Cambodian Archaeological Lidar Initiative.
And it started to become fairly common-place as an archaeological method in the last 5 or 6 years, beginning in particular with applications in the Maya world. And there's a misconception that LiDAR (these laser scanners) can somehow penetrate or directly see through leaves or vegetation or see what's underneath the ground. In fact, that's not the case at all. What the instrument does, is it's take advantage of the fact that, even in the most dense forest canopy, you can still see gaps in the vegetation where light is shining through.

And so what you do, is you fly with this aircraft over forested areas; the instrument fires off millions and millions of laser pulses every few seconds. Almost all of those laser pulses just bounce right back of vegetation, of trees, and this kind of thing. But a very small percentage of those laser pulses find those tiny gaps in the canopy, and make their way to the forest floor. And using sophisticated algorithms back in the office, you can essentially filter out vegetation from the picture, and you're left with a nice picture of the topography underneath that canopy.

And not just in a 2-dimensional profile like that either, but in a swath, in our case about half a mile away. Again: most of which is just vegetation, trees, and that kind of thing, modern development; but using algorithms we can basically remove that from the picture. And we fly very systematically in a grid over particular areas, and turn those point-clouds into 3-dimensional images.

And so whereas before we look from above, and see something like that; essentially just forest and [...] fields; using LiDAR and these algorithms we can identify all of the points that are not on the ground (not-ground points: points that hadn't returned from the bear earth) and differentiate them from bear-earth points and create a bear-earth model. And we can see the existence of large state temples. This particular one was known, but we have been able to reveal a whole network of other ancillary temples, a network of infrastructure connecting those temples to the main one, patterned occupation mounds. That kind of thing. And so it's really a remarkable advance in our ability to see archaeological landscapes beneath the vegetation.

And so what we did is we launched a LiDAR campaign in 2012: the very first LiDAR campaign that had ever been undertaken by archaeology anywhere in Asia, as far as I am aware. We were inspired by some work that some Mayanists had done in Belize, and flew over these forested areas around the centre of Angkor. Because it was very difficult to raise money during this period, I kind of had to pass the hat around to various different international teams and people threw in whatever amount of money they could afford to lose. We weren't sure if the technique would really work in this environment or not. And so we ended up with a kind of strange patchwork of different places based on the priorities of the 8 teams who were involved in this original project.

  • Caption: An oblique view of Angkor Wat and its immediate environs. Upper layer: Digital orthophoto mosaic, with elevation derived from the lidar digital surface model at 1-m resolution. Lower layer: extruded lidar digital terrain model, with 0.5-m resolution and 2× vertical exaggeration. Red lines indicate modern linear features including roads and canals.
  • Source: "Airborne laser scanning as a method for exploring long-term socio-ecological dynamics in Cambodia", in: Journal of Archaeological Science, 2016.

  • Caption: An overview of the LiDAR acquisition areas in northwest Cambodia (background data courtesy of the Shuttle Radar Topography Mission).
  • Source: "Uncovering archaeological landscapes at Angkor using LiDAR", in: Proceedings of the National Academy of Sciences of the United States of America [PNAS], 2013.

So, just to give you an idea of the outcomes of this 2012 project, looking at this area around Angkor Wat here, in the centre. This is a satellite image of that particular area, where you can see that it's quite densely covered by forests [...] the temple of Angkor Wat there, surrounded by forests and its moat, and a patchwork of urban areas and forests around.

  • Caption: Conventional high-resolution satellite imagery of the central area of Angkor, showing archaeological topography obscured by forest.
  • Source: Google Static Map Maker (click here to open the image if the bottom image failed to load).
Before LiDAR, the best map that we had of this area was produced by Christophe Pottier in the 1990s, using aerial photographs and ground survey. And you can see he has done a fair job here, even managed to identify some linear features, embankments, some ponds of occupation mounds: not a bad effort at all, considering the amount of vegetation that covers that area.

  • Caption: Previously documented (prelidar) archaeological features in the central area of Angkor, showing the "walled city" of Angkor Thom above Angkor Wat.
  • Source: "Uncovering archaeological landscapes at Angkor using LiDAR", in: Proceedings of the National Academy of Sciences of the United States of America [PNAS], 2013.
The LiDAR, of course, adds a completely new dimension to that picture, and shows that the engineered landscape around this temple is immensely more complex than these pre-LiDAR maps we had us believed. So you can see for instance, a very neat chequerboard pattern, of mounds and ponds within the central moat of Angkor Wat. And you can also see that very patterned urban space: again a chequerboard pattern of mounds and so on, extending on the outside of Angkor Wat as well; in addition to these rather enigmatic spiral geometric shaped features to the south of Angkor that we still learn, but don't really understand. As a result of this LiDAR, we just finished re-mapping this central area around Angkor Wat, which; as you can see; is a great deal more complex (much more interesting, much more densely inhabited) than previously imagined. So you had to completely revise our view of what the city [...] Angkor Wat would have looked like.

  • Caption: The central area of Angkor, showing the “walled city” of Angkor Thom above Angkor Wat. Upper: lidar digital terrain model, with 1-m resolution. Red lines indicate postmedieval linear features including roads and canals; other features are Angkor era.
  • Source: "Uncovering archaeological landscapes at Angkor using LiDAR", in: Proceedings of the National Academy of Sciences of the United States of America [PNAS], 2013.
  • Caption: Detail of the archaeological landscape south of the moat of Angkor Wat from LiDAR imagery: top, combined hillshade and digital elevation model derived from LiDAR ground returns; bottom, preliminary map of archaeological features visible in the LiDAR data (LiDAR courtesy of KALC).
  • Source: "The landscape of Angkor Wat redefined", in: Antiquity, 2015.
This is a pre-LiDAR artist impression of that city: you can see the artist has buildings of different sizes and different orientations. He hasn't put any ponds in there, there's large open spaces.

We now know from the LiDAR imaging, this is a completely in-accurate representation of the city around the temple, and that in fact it would have looked much more like that: much more rigidly organised, and densely occupied than we thought before.

  • Caption: Reconstruction image of Angkor Wat on the basis of the LiDAR images and recent fieldwork by the Greater Angkor Project (image courtesy of Tom Chandler, Monash University).
  • Source: Published in "Angkor Wat: an introduction", at ResearchGate.
And archaeologists since this campaign in 2012 have been out there on the ground, excavating these house mounds, trying to work out who lived within the moat, in these particular spaces.

So, just to give you another example of the power and the capacity of LiDAR to move research forward, one of the most interesting outcomes was here in the great wall city of Angkor Thom, which dates from the 12th to 13th centuries. This was built by Jayavarman VII, the same king who built Banteay Chhmar, and it's an enormous moat and enclosure: 3 kilometres long on each side. The very famous temple of the Bayon in the middle, with its face towers and so on. And here we were very lucky actually, because; beginning in the 1990s, some colleagues of mine at the École française d'Extrême-Orient; in fact began a survey of this area the old-fashioned way: on the ground with machetes and hand-survey levels and spent years and years mapping these subtle variations in the terrain. And what they've done is they produced a quite amazing archaeological of this area; this huge area: it took them years to do; which shows very clearly the existence of a grid of canals; many many canals and some ponds inside that wall area. And also the foundations of where the old royal palace used to be. And this was great for us, because we had a data-set; an archaeological data-set acquired the good old-fashioned way; against which to compare the validity of our LiDAR results.

And it turned out that our LiDAR results accord almost perfectly with this data-set that had been achieved on the ground. The key difference being that, instead of years and years and years of field-work with machetes and this kind of thing; we managed to achieve the same results in an hour or two of flying time in the helicopter. Which gives you an idea what an incredible leap forward this is, for those of us interested in the history of these lived-in spaces. Also, it turns out that this grid didn't just exist within the confines of Angkor Thom, but extended far beyond as well. And so you can see that grid extending out into other areas, including the famous temple of Ta Prohm, the one with the super-iconic temple of Angkor with the strangler figs enveloping the stones; as well as various other temples in the area ... that all were incorporated into this down-town area: this very densely inhabited urban core, which turns out to be about 4 times bigger than just the wall enclosure that we used to think it was. So, a very very different perspective.

  • Caption: Map of the present state of the central area of the Angkor Archaeological Park. The distribution of monuments in Angkor Thom is based on Gaucher (2004b). Depressed linear structures, earthwork, ponds and recent rice field patterns are identified in the RRIM map. The distribution of dense forest and vegetation is shown based on satellite photo. While many depressed linear structures and ponds can be confirmed in the dense forest, no such vestiges were found in wet-rice cultivation fields. The distinction between new and old water channels (depressed linear structures and recent channels) includes channels that are difficult to decipher at present. In particular, it should be noted that there are cases where a new water channel was built using a water channel that existed during the Angkor period.
  • Source: "The Advanced Hydraulic City Structure of the Royal City of Angkor Thom and Vicinity Revealed through a High-Resolution Red Relief Image Map", 2016.
  • Caption: The central urban grid of Angkor extending from Angkor Thom (top left) and Angkor Wat (bottom left) past the temples of Ta Prohm and Banteay Kdei (moated temple-sites on top right), visible in a combined hillshade and digital elevation model derived from LiDAR ground returns (LiDAR courtesy of KALC).
  • Source: "The landscape of Angkor Wat redefined", in: Antiquity, 2015.
One of the interesting outcomes of the 2012 campaign, something that was in the news a lot a few years ago, was that one of the very first cities of the Angkor area was up here in Phnom Kulen; it's called Mahendraparvata: it was known mainly from inscriptions, there were some large temples up there and so on ... but no-one had mapped or really understood how the city was laid out in any kind of detail: just basically a series of disconnected dots on the map. In the 2012 LiDAR campaign to go up there, fly up around this remote mountain plateau, and look through the forest, and basically uncover the remains of this city of Mahendraparvata. It wasn't a lost city as you would hear in the press; in fact none of them are really. We had a fair idea that this city was there, based on the existence of temples, inscriptions that refer to the city being there, and so on. But if you have a look at this image, what's marked here on this 3D-representation of the LiDAR data; in green are the elements that we know before the LiDAR, and in red [...] the elements that we discovered after the LiDAR: as you can see, that's basically the city revealed with incredible complexity for the very first time.

  • Caption: Mahendraparvata. Shaded relief map of terrain beneath the vegetation in the Phnom Kulen acquisition area, with elevation derived from the LiDAR digital terrain model at 0.5m resolution and 4x vertical exaggeration. Green denotes previously-documented archaeological features; areas shaded red contain newly documented features indicative of an extensive urban layout.
  • Photo: Archaeology and Development Foundation - Phnom Kulen Program/Handout PNAS News.
  • Source: "Airborne laser uncovers ancient hidden city near Angkor Wat", in: National Post.
What was also clear is that the city extended beyond that coverage area. You can see this network of canals, infrastructure, and roads and so on. Obviously, it just doesn't end at the end of our coverage; but must extend much much further. So what we did is we built on the success of the 2012 campaign to raise money from the European Research Council for a new coverage which we completed in April last year: the 2015 LiDAR coverage, which is the one that's just made the news this weekend.

And there is an image of the helicopter that we used: basically the same set-up than we used as last time: the next generation LiDAR instrument ...

  • Caption: For the 2015 acquisition we’re using a Leica ALS70 lidar instrument with full waveform capability, mounted to the right skid of a Eurocopter AS350 B2 “Squirrel” helicopter. For the install we have to remove much of the interior of the chopper and replace it with special computers, power supplies, GPS upgrades and additional avionics. The helicopter is the same one that’s used for tourist flights around the Angkor Archaeological Park, and the same helicopter we used last time in 2012, although the lidar instrument we’re using this time around is capable of much greater point densities than the ALS60 instrument that we deployed last time. We also have a 40 megapixel Leica camera looking straight down as well as a forward-facing Canon EOS 5D at the front of the pod to take oblique aerial shots of what we’re flying towards.
  • Photo: Francisco Goncalves.
  • Source: Cambodian Archaeological Lidar Initiative.
One of our main priorities was to greatly extend our coverage of that remote mountain range to the north of Angkor, which comes to terms with the true size of the city of Mahendraparvata; and also find out what else is going on up there, in those mountains, looking at occupation, the extension of Angkor into the forested areas.

It's also where the stone came from, from the temples; so we can use the LiDAR to find quarries. This is the sort of work, obviously very important for a number of reasons.

What we also did in the 2015 campaign, is to extend it to the capitals that heired before Angkor Wat, the capitals that heired after Angkor, and provincial, industrial and military centres like Preah Khan Kompong Svay and of course Banteay Chhmar. And so, just to give you a couple of examples of the outcomes of that 2015 campaign: what we were able to do, if we look at that mountainous area to the north of Angkor, is that we were able to identify the full extent of that city of Mahendraparvata to the North. It turns out we got most of it the first time around actually, but that's the extent of it there. It turns out to be really really big, the size of a lot of modern cities in the region of South-East Asia. And we also found a lot of other evidence, it's not like we didn't find anything in this area: there's lots of other evidence for occupation, temples, that kind of thing, as well as quarrying and so forth. So a really quite fascinating set of outcomes in that particular area.

Just to give you a final example: one of the things that was, in my opinion, the most spectacular outcome; of the 2015 campaign; are the results of the city of Preah Khan Kompong Svay in Preah Vihear province in North-West Cambodia. So, this is a quite enigmatic site actually. If you look at a conventional satellite image, you can make out that it has a huge enclosure around; in fact the largest enclosure in pre-modern South-East Asia: it's about 5 kilometres on either side. And also a very very large reservoir here as well.

  • Caption: Conventional high-resolution satellite imagery of Preah Khan of Kompong Svay.
  • Source: Google Static Map Maker (click here to open the image if the image failed to load).
And there is a very very substantial and heavily looted sandstone monument in the middle of the complex. And myself and my colleague Mitch Hendrickson, from the the University of Illinois at Chicago, had spent about 10 years at this place working; trying to work out where the people lived, where was the city surrounding this particular temple. What we'd done is, used basically every method at our disposal, on the ground and from the air: doing pedestrian surveys, using radar imagery, satellite imagery; everything at our disposal; and basically came to the conclusion that there was nothing much going on inside that enclosure, aside from a bit of iron working and smelting. And, in fact, we published a paper between the two of us last year, which showed an updated map of this site of Preah Khan, with the temple in the middle, and really not a great deal going on in the rest of the enclosure.

Unfortunately we probably should have waited for the LiDAR results to come in before we published this paper. It was too late to pull it out of press by the time the pictures came in. But, to give you an indication of how LiDAR is such an improvement over these traditional methods, we can see, in fact, the LiDAR image of the same area. On that scale, you can't see much; but if we zoom in to this central area here; just to give you an example; in fact you can see that, not only do you have that temple in the middle there, but you also have the remains of a wonderful 100 meter by 100 meter urban grid inside the temple moat, just like almost every single one of the temples of the 12th century that were built by the Khmer; and once again you can see that city extending expanding on the outside as well: this network of canals, and ponds, and so on. And this stuff had more or less been hiding in plain sight for a decade. We tramped all over this endlessly, and just've been completely unable to see it or to map it. And it was quite striking actually to have this kind of revealed on the screen in front of us, after the LiDAR data delivery. And here you can even see the degree of complexity, as revealed by the laser data, compared to this quite embarrassing map which we unfortunately [...] published in December last year. Very very different from the kind of imagery that you see in the LiDAR data.

  • Caption: Preah Khan of Kompong Svay: one of the major ‘temple cities’ at the height of the Khmer Empire in the 12th to 13th centuries CE. Showing developments associated with king Survayarman II (first half of the 12th century), with areas within the moat divided neatly into ∼100 × 100 m ‘city blocks’. This is not a development associated with king Jayavarman VII (late 12th century to early 13th century), which would show much greater variability in spatial patterning.
  • Source: "Airborne laser scanning as a method for exploring long-term socio-ecological dynamics in Cambodia", in: Journal of Archaeological Science, 2016.
So, one of the other places that my colleague Dr. Sharrock will talk about in a moment, is Banteay Chhmar. We covered this area as well. This was another place where we really spent probably again about 10 years looking for evidence of a large and complex and extensive city arround the major temple complex. If you zoom in to our coverage area in the LiDAR: there's the main temple there with its huge reservoir. That's an image, a conventional satellite image, of that area. You've got the temple within its moat; the large reservoir there; it's obscured a lot by vegetation and by contemporary urban remains. And this is a LiDAR image of the same area. And [...] uniquely; well, not perhaps; but definitely uniquely amongst all of the major temple sites; Banteay Chhmar shows very particular evidence for a formally planned urban grid either inside or outside of its moats or successive enclosures. And so it's a real mystery for us, actually, this particular place; which Peter [D. Sharrock] might have more comments about. In fact, as you can see, the LiDAR data really doesn't add much insight to the maps that we had of the place before: it's really much the same as the maps that we created using regular satellite imagery. And indeed, you can zoom in to that central area there, and we can have a look beneath the modern occupation and the trees, and we can see that [...] really not much is going on inside that enclosure, aside from the existence of a couple of ponds. A bit [...] the south, you can see, even beneath the forested area, that there's some; maybe; some evidence of some linear features and a couple of ponds and so on. So, there's something going on inside that enclosure; but whatever it is, it's totally different from the rest of the temples of this 11th, 12th, 13th century period in Cambodia's history.

So, in the interest of time; I think I'll leave those examples there. And just as a final point I'll make of these great engineered landscapes of Khmer are not the only ones that exist in antiquity. So, even as we sit here; there are archaeological projects all around the world that are undertaking projects, large-scale acquisitions of airborne laser scanning data, peeling back vegetation and revealing ancient landscapes. And it's quite interesting; because a community of scholars has emerged which are interested in this sort of dynamic interaction between humans and their environments. And the whole thing is underpinned really by LiDAR data-sets: people sharing data-sets that are incomparable and that can be used as the basis for an emerging global comparative archaeology of early urbanism in the tropics. So, this is one of the areas also where the study of past really begins to resonate with a range of contemporary issues about the sustainability of these sites and so on. And we should look forward to seeing a range of the [...] sites from LiDAR projects in the coming years; hopefully reported a little bit less sensationally than the discoveries in Cambodia, so that the whole point of the research doesn't become lost in the hype.

Anyway, on that note, I would like to thank you for your kind attention, and at this point I'll pass the floor to my colleague Dr. Peter Sharrock. Thank you.


Peter D. Sharrock's main speech

Banteay Chhmar didn't produce the results we had anticipated. We anticipated a very large city in Banteay Chhmar, the second city of Cambodia. Because of the temple construction there. There are 2 major inscriptions which give us an account of the history of this temple. One is in Banteay Chhmar, the other one is in Vietnam, in the former country of Champa. And if you put these 2 sides of the story together, with what we know of the site, we have 3 sources of information; it's quite brief; on one temple, and what was happening with this temple as a base in Cambodia. Not much has been written about Banteay Chhmar because there has been no excavation. The French went there in the 1930s, photographed it; fortunately; and then more or less left it. They were too busy, there was too much to do in Angkor itself and elsewhere. So, it's one of the outer sites which has been little studied.

But in recent years, scholars have looked at the 2 inscriptions which talk about this king's extension of his power to Champa. Its predecessor, not its immediate one but the one before: Suryavarman II, the man who built Angkor Wat, had arranged a deal in Champa; which, in return to Khmer engineering skills (water engineering skills) seeded a certain amount of territory to the Khmer. So together they were going to build a huge dewatered port, where both peoples would profit from the expansion of the [...] dynasty in that period: in the 12th century [...] China was organized again and was growing enormously; and both countries wanted profit from it. However, the Khmers lost control of the port in Champa, because the Chams envaded angkor. And in 1177 they actually hit Angkor, burned the palace, and killed the king. It's the only ever raid of Angkor. They then went back, we think probably needed [...], but Cambodia was in a mess for about 4 years: it was in a sort of state of civil war. And this king, who was not the most correct or the strongest claim to the throne, emerged from that war, as the king; the king of kings; the king of Khmer kings; because there were many Khmer kings. And he turned out to be most powerful, the most successful, and he had a very long reign. So he came to the throne in middle age, already a great general, and with very very big ideas for where to take the country and, in particular to promote Buddhism. Because Angkor had been Hindu for most of its; or at least for the first 200 years of its life; Buddhism was there, but as a second religion, faith. Both were more or less tolerated. He wanted Buddhism; the Buddhist umbrella; to cover the whole empire, and that's indeed what he did.

A new inscription has just been discovered in Paris; where a collector bought a stone with a lot of writing on it, and very unusually went to the EFEO (The French Institute for Eastern Archaeology), French school, and said: 'could you tell me what it says?' Apparently most collectors buy these stones, and they don't ask; they just keep them because they like them and the writing is beautiful. This one has just been translated, and we discovered a whole new Buddhist king who was in fact the younger brother of Suryavarman II, and he built 8 Buddhist foundations in Angkor, and he reigned for 27 years. So we have another major Buddhist king in Angkor. His dynasty went back to 2 predecessors in the previous century, who were also Buddhist kings; but they did not do what this king did: they did not impose Buddhism as the major, the dominant religion of the state. Now maybe [...] that stretching the Buddhist umbrella over Angkor didn't actually move the Brahmans out; or it's more or less that they were accumulated within the state. The Brahmans had lots of key functions, and they continued to fulfill those functions and they still do today. The Buddhism is no longer Mahayana in Thailand and Cambodia, but there are Brahmans of course, who carry out the ancient rituals of coronation [...] the annual rituals of both states and [...] they have high status in the society. So, the Hinduism, the Brahmans, remain; but the umbrella of Buddhist philosophy was stretched over them by this king.

The interest of Banteay Chhmar is that some of the Buddhist temples in Angkor were actually attacked about a 100 years after Jayavarman: 1 king, I think it was in 1327, so a 100 years after the king died ... 1 king turned the Bayon; which is this great Buddhist temple that Damian was talking about; back to Shiva worship. So we find shiva lingas erected in the Bayon: 6 of them; and quite a lot of engravings of Buddhas were chiselled into shiva lingas. So it was turned to Shiva rituals. And, in the process, many small Buddha figures were chipped out of the walls of other temples. So there is signs of Buddhism coming under attack in Angkor. It's the only time it happened, and I think it happened within a couple of years; and it's much quicker to remove things than to carve them again anew. So that was 100 years after this king.

So the desecration, for some reason, does not appear in Banteay Chhmar. So there is iconograpy in Banteay Chmar, which only exists there. So it's a unique source for art historians and archaeologists, from that point of view. I call it, in my book [Banteay Chhmar: Garrison Temple of the Khmer Empire], a Garrison temple, because the story of the 2 inscriptions I told you about (the main inscription from the temple, and the one from Champa) talk about a prince who led the Khmer army to Chapa; which is a long journey, over the mountains; into Vietnam, to install the prince as king of Vijaya. This prince seems to have come from Banteay Chhmar. He didn't survive very long on the throne, the Chams were powerful military people: they rose against him and removed him after about a year, and he fled back to Cambodia. In Banteay Chhmar; if you put the 2 inscriptions together; and you look at the engravings of the walls of the temple, I think we can ... we find that story of the prince going to Champa and coming back. And the main inscription of Banteay Chhmar to venerate the generals who died during that retreat from Champa. So they were deified: they became gods. And the main inscription is to venerate them and their deeds, preserving the life of the prince who had been very briefly king of Vijaya.

The lack of desecration means that the iconography is quite unique. And there are icons in Banteay Chmar which are unique: there is a famous road of 8 bodhisattvas; the compassion bodhisattva avalokiteśvara large man-sized along a whole wall: quite unique in Cambodia. And this was unfortunately the subject of an egregious looting event when a number of tracks; apparently with high personnel on board; took down 4 of the avalokiteśvaras, and took them to Thailand. I will get around to that in a picture shortly.

So the reliefs of Banteay Chhmar; for those of you who have been to the Bayon temple, you will remember the reliefs; Damian [Evans] showed one; of an army fighting on the wall. This was an invention of this period, that politico-military reliefs of contemporary life and major political events were reported on the walls of the temple. Inside the temple you had the gods, but on the outside was the world [...] king.

LiDAR has now given us an incomparable new base on which to go and explore on the ground in Banteay Chhmar to understand why it is the way it is. Now, this is one of the face towers, which was the mum of the rei Jayavarman VII. Who is the deity in the face tower is a major question. There is still no consensus on this. My view of it, is that it is an esoteric tantric Buddha: the sixth Buddha of esoteric Buddhism, called Vajrasattva; and that the face towers are part of a mandala of state which Jayavarman brought into Cambodia. The mandala of state ... this one is, by the way, the first face tower that has been restored by anastylosis: a smart greek word for say "build again"; so, you take all the stones down, you clean them, and put exactly the same materials back, filling in where necessary but in a minimal way; so, by anastylosis. It's a very complicated structure: they hollow it out on the inside; it's a very delicate structure, and I have to credit to the Global Heritage Fund for attempting this: this is the first one that has ever been restored fully, and I think; you have to agree; it's looking pretty good. There are all sorts of interesting traces of [...]; that statue found right underneath, in the sanctuary, under the face tower.

"Banteay Chhma", rather than "Banteay Chhmar": if you remove the final 'r' from the name, it's "the citadel Banteay, the second citadel", rather than "the citadel of cats". So, this is a word that has gone into middle Khmer: it's not the original word at all, it would have had a Sanskrit name but that is lost. But "Banteay Chhma" means "the second citadel". Why would it be the second one? Well, because there are 59 face towers, according to Olivier Cunin's calculation, in the Bayon temple in Angkor; and 50 in Banteay Chhma, so the Buddhists supporting this kingdom were geographically placed in these 2 places. So, this was highly significant in religious terms. And because we now know that the expedition to Champa was mounted from Banteay Chhma, it was also militarily very significant, which is why I call it a Garrison temple. Apparently not a great population centre. But it could have been a place to raise an army to go on a large expedition without a large population centre: it could have perfectly well have fulfilled that. My own guess about this anomaly of the low population data that LiDAR is bringing out in Banteay Chhma is that it was possibly a late city that was incomplete: because it does have a massive water system, coming from Dangrek mountains, in canals, to fill the moat of Banteay Chhma. So, it was set up to sustain a large rice-growing agriculture and a large population; so it's possible that it was simply never completed and never built into a large city. The military function: why raise an army in Banteay Chhma, when you could have raised it in Angkor which would have been a 100 kilometres closer to Vietnam? I think that was probably a political calculation, that he would safer ... the king didn't have the best claim to the throne which he just possessed, and he did have many rivals: and many of them were Hindu, some of them were Buddhist, so my guess is that he raised the army for that large acquisition in Banteay Chhma, which was traditionally a Buddhist area of the Khmer empire ... it was safer to raise it there, than to raise it in Angkor, where it could have been used against him.

This is another surprising thing about the scale of Banteay Chhma: it's much bigger than the Bayon. The Bayon of course is in the middle of a city: it is a very very large and dense structure. Banteay Chhma is much more spread out. This is Olivier Cunin's drawing. But the reliefs that you look at in the Bayon are here, and they are mostly incomplete. They are very interesting. In Banteay Chhma they are twice as long, and much more complete. Unfortunately, they are mostly lying on the ground. So we have to get in with conservation effort, to raise them and we will learn a great deal more, and we will able to connect it with these 2 texts that we've already got.

So this is again the mandala of state, this is the height of a man, at the Bayon. And there are 3 in the picture of the 59 all together towers with 4 faces. And these are the ones from Banteay Chhma ... slight differences in style, but just as majestic and powerful and imposing under a tropical forest in a large ruin. Here is [Olivier] Cunin's picture: the mandala is a circle, with the king at the centre and subsidiary kings all around. We think of mandalas as being flat, actually they were pyramids and based on a circle. So, if Angkor was the centre, Banteay Chhma was here; and the only other place [...] in Preah Khan of Kompong Svay; which Damian [Evans] was talking about earlier; so it looks as though the geographical extension of this mandala is something like that. That is not fully understood, but it seems to be the circle of state of Angkor.

So that is what the conservers are confronted with today: huge amounts of rock on the ground, huge amounts that need careful lifting up; and pathways cut through so that visitors and tourists can go through ... with a good deal of carving ... so there are ... LiDAR has given us a great leap forward, it has given us a map of what is there: what the old city was ... but there are decades of work to be done on the ground, restoring this temple, as best as we can.

That is our inlook in its pristine state, according to [Olivier] Cunin's computer reconstruction. With sanctuary centres [...] here ... face towers in critical places, a shiva temple up here. And the external walls with the reliefs outside ...

  • Caption: Architectural Reconstruction of the Central Complex of Banteay Chhmar. Sponsored by The Robert Kiln Charitable Trust in collaboration with the Global Heritage Fund.
  • Visualization: Olivier Cunin
  • Source: Visit Banteay Chhmar.
So this is the graveyard stones; where the Global Heritage Fund took down the east part of the eastern gallery, cleaned it, and put it back. But there is so much more to be done, in exactly the same way. We can now read what is going on on this [...]

This is the prince Banteay Chhma, we knew nothing about him before. He doesn't exist on the Bayon. The king appears all over the Bayon, he's always much larger than everybody else. Here, he appears with this prince. So this seems to be the duke of Banteay Chhma, who was commissioned by the king to go to recover the territory in ... so; Indravarman is his name in the Banteay Chhma inscription.

And here we have the king again, with the sword of state; the prince sitting in front of him; the Brahmans with the large hats, in an important ceremony. My suggestion is a chalice coming up, with holy water. I think he is making him; he's crowning him king of Vijaya, in Champa, before he goes off with the army. The army is down here: officers looking back, and the soldiers walking on. So, I think that is a scene which is the beginning of the Vijaya expidition.

One other function of Banteay Chhma is the medical function, because the Khmer empire; not only conquered by military means, it also did it by medicine. This king produced the earliest national health service: he produced a 102 hospitals, provided with medicinal herbs, staffed them; and they were open to everyone; and most of them positioned outside the cities. So this is 200 years before the first hospital in Europe. Quite an extraordinary event, and it looks as though; in North-East Thailand ... first of all, Banteay Chhma is next to the Dangrek mountains, and the herbs grow in the mountains, and the animals whose parts also contribute to medicine, lived in the mountains. Also gold produced in medicine, was found in the mountains. So, everything was [...] in Banteay Chhma ... it looks as though it was positioned there partly as the service centre for this whole network of hospitals. So the gathering and blessing of the herb; the medicinal herbs that were then distributed; would probably been taken place in Banteay Chhma.

And here, I think, is a scene where the king is making an offering, and we used to think it was a rice festival. I think it is possibly a medicinal festival.

Here are the sacks containing something that everybody is very focused on.

There are a group of merchants, with little piles of gold in front of them; who, I think, are the middlemen in the pharmaceutical business. So they are gathering things, transporting them, mixing them, and so on.

Now this is what happens in Tibet today: every so many years a huge amount of medicinal herbs are brought together; put in these sacks; and for several days there are blessing operations that go on; and then it's distributed right across the Himalayas. And everyone in Tibet has a little bit of this mixed medicine: it's not 1 herb for 1 problem; it's having a little bit of it in your house all the time, and if you get really ill, you will take it, you will ingest some of the medicine. But, if you don't get the blessing, it doesn't work. So the great ceremony to bless the herbs. So, I think, Banteay Chhma; when I go back and try and discover what its role was; it seems to have been a key part in the mandala of state, it seems to have a key military role, and it had a medicinal role with [...] amazing hospital [...]

These are the 8 avalokiteśvaras on the western gallery: these are the only 2 which are left standing ... computer reconstruction ... these are 2 which were stopped by accident in Thailand. A policeman said: "Can I look at this cargo of meat products that you have in your truck?" And it turned out that it was part of Banteay Chhma. Eventually the Thais [...] allow them to go back ... they are now: there they are in the Bangkok museum, because they thought it must have been that they were from a Khmer temple in Thailand ... but they were completely unique, so they've actually gone back to Cambodia and they are now being re-installed in the Phnom Penh National Museum [of Cambodia]. Eventually, when Banteay Chhma is safe enough, we all hope they will go back to Banteay Chhma.

These are 2 which are lying in the grass [...] this is a major job.

So, 2 are still standing; 2 are in a museum in Phnom Penh; 2 are in the grass; and 2 are still missing ... The Cambodian Ministry of Culture and Fine Arts would love to have them returned. So they are going [...] we don't know where they are. We guess that they are in Bangkok; but we just don't know. But one of the objectives of the Cambodian government, at present, is to return these to Cambodia. And these are 2 absolutely key items on Banteay Chhma. So they are quite high up on the political list of things to be repatriated to Cambodia. Thank you.


Questions (Q) and Answers (A) session with the audience

Q: A speaker of the Global Heritage Fund

I have a question: Damian [Evans] ... [...] can you tell me a little bit about the Khmer involvement in your scheme, in your LiDAR scheme; and how that sort of obliterating through [...]?

A: Damian Evans (1)

So, in the last slide, Eric; [...] the campaign that we carried out last year: the LiDAR campaign. It's a joint effort between the Ministry of Culture and Fine Arts, responsible for places like Banteay Chhmar. The APSARA National Authority [National Authority for the Protection and Management of Angkor and the Region of Siem Reap], responsible for Angkor, its mountainous areas to the north of Angkor; and also the EFEO [The French Institute for Eastern Archaeology] as well. And so a large part of the work that we do involves training and capacity building, and in fact we have reached the situation where Cambodia has the largest archive of archaeological LiDAR data of any country in the world. [...] And as heritage managers, so as far as I'm aware they are the only ones who routinely use it for decision-making purposes on a day-to-day basis about planning, construction [...], archaeology, and that kind of thing; so Cambodians and Cambodian institution are really at the fore-front; not only of research applications, but also practical applications in terms of heritage management.

Q: 'A lady in the back'

Hi, Damian [Evans], a question for you: I saw on one of your slides that you also looked at Sambor Prei Kuk. Could you tell us a little bit about what you found there?

A: Damian Evans (2)

Sambor Prei Kuk is quite interesting: this is the pre-Angkorian capital; the capital [...] basically immediately preceded Angkor. And a Japanese scholar did his PhD thesis on the site, in 2010-2011. [...] to map a fairly elaborate network of ponds and other infrastructure surrounding the lawn mowed temples. And so we had a pretty decent map of Sambor Prei Kuk to begin with. Once again though, LiDAR adds a whole new dimension to that picture: so things that were mapped as being walls turned out to be moats, or canals connecting to other moats, and that kind of thing. So [...] a hydraulic network of running through and among the temples that had been mapped before using conventional imagery. So, in some places like Preah Khan Kompong Svay, essentially it's fair enough to say that entire cities emerged, completely surprisingly, from underneath the vegetation. In other areas, a quite reasonable amount of work had already been done. But in even in those areas, the LiDAR adds up an extraordinary level of precision and definition to the archaeological maps that already existed.

Q: 'A man in the front'

Could I ask: when you were mapping the canals, did you find a technology to change levels without lock gates?

A: Damian Evans (3)

They did. In fact, one of the key problems; one of the reasons for the eventual break-down of the system, is that because they cut down all of this forest in the northern region of Angkor, what happened was that the monsoon rains come down very hard and very strong during the wet season in Angkor, and normally you have this large forest buffer, basically to even out the flow of water rushing into the system. Of course, without that buffer; when the forest is all cut down; the waters from that northern [...] thrust very very quickly into the system, and what would happen is that the water would run so fast that it would, inside into the ground, down-cut: the canals became much deeper than they should have been, and things didn't flow nicely from one level of the system to the other. And then of course when the water finally reached low-energy environments like these huge reservoirs that [...] because of that sediment, and similarly caused problems for this kind of sedimentation. This is the problem of this system. And so in order to devise solutions to these various problems that were caused by the forest degradation, they developed schemes of weirs and dams and so on, to brace water levels and this kind of thing. But, you know, the system; I think; I don't think ever really worked all that well. What would happen is that they would build a reservoir with a water entrance system in one area; it would fail after a couple of 100 years; they migrate to another place, build another bigger better reservoir which would also fail after a couple of 100 years; and then they would rinse & repeat over and over again. And they managed to muddle their way through over the course of many many centuries, until; in the 13-hundreds & 14-hundreds, they were faced with droughts of 20 or 30 years in duration, which were really un-liable to be compensated for by the existence of these quite problematic water management systems. The [...] ; the canals and so on were also made of earth, so they were prone to things like erosion and so on. Very few structure in the water management system were actually made of stone: a couple of spillways, 1 or 2 dams, 1 or 2 [...] and outlets to the reservoirs. So it's quite a delicate system, which was subjected to [...] fractures of their own making.

Q: 'A lady in the front'

The new technology that you spoke about tonight reveals patterns under the ground. Do you have any sense what actually is under-ground: is it still some wooden structures, houses, ... what do you expect to find there?

A: Damian Evans (4)

The LiDAR doesn't ... just to sort of clarify the first point ... the LiDAR doesn't reveal structures beneath the ground, it reveals only this topography. One of the things that makes archaeology so interesting; aerial archaeology so interesting in Cambodia, is that the cultural deposits tend to be very very shallow. So normally, during excavations, we dig down 1, 2, maybe 3 meters at the most: so these are very very close to the surface. And we have cultural remains so close to the surface; normally when something was buried under-ground, you find some kind of surface manifestation. The thing is that would have been buried underneath the ground, centuries ago, things like the remains of wooden structures and so on, would have completely rotted away. So, what we find, when we excavate this patterned archaeological topography, tends to be things like post-holes, things like potsherds. Basically 99% of the archaeological material that comes out of these places are just potsherds ... which we can tell a fair amount; about who lived there; on the basis of these potsherds. For instance, within the moat of Angkor Wat, we have done a fair few excavations then, looking at this kind of household archaeology, and contrary to what I expected, but a lot of my colleagues seemed to think of as the way it would have been: the kinds of potsherds we found was very very simple, domestic [...] there were no [...] corporate [...] elite [...], within the moat of Angkor Wat. You can also look at things like post-holes, so the residents that lead people [...] were much more substantial and had much larger post-holes remaining in the soil. The houses of elites also would have had ceramic roof-tiles or; ornate ceramic roof-tiles; whereas the houses of ordinary people had roots of thatch. [...] the main archaeological record as well; so even just from looking at the potsherds that remain; we can [...] who lived in these kinds of places; but that's our main source of evidence.

Q: 'A man in the back'

First of all, thank you very much for the presentation; that was lovely. Out of curiosity, as a user of LiDAR: what company did you get, what kind of LiDAR equipment was it; was it for instance; from [...] like Z+F [Zoller + Fröhlich], [...] or ...?

A: Damian Evans (5)

It was a LiDAR ALS70 in full waveform mode.

Q: 'A man in the back'-2

Was it custom-made for this?

A: Damian Evans (5)-2

No, no. The pod that we attached to the helicopter was custom-made. I mean: basically we used an off-the-shelf LiDAR system, the latest generation of it. But we ... the instrument doesn't belong to us: we hired a LiDAR engineering company; a Canadian company called McElhanney, that are branched in Indonesia. We gave them a contract on both of our acquisitions actually. They come over to Cambodia, they brought that big black fibreglass pod, they bring the instrument to fit inside of it; then we rent the helicopter locally, and get our surveyors locally and this sort of thing. So we kind of do it on the cheap by bringing things in, and bringing people together rough than pay a company come in and do everything for us, or even worse: buying one of these things for ourselves. Because the whole ensemble is worth a couple of million dollars, which is reasonably expensive for an archaeologist.

Epilogue by the host, of the Global Heritage Fund

Thank you very much Damian [Evans], and thank you very much Peter [D. Sharrock].

[...] Peter [D. Sharrock] will be running a tour with our sponsors ABOUTAsia Travel, to Cambodia; visiting some of the most interesting sites, and he will be illuminating them as you have seen him doing this evening in an incomparable way; that runs from the 8th to the 14th of January in 2017.

Thank you very much to our hosts of the Royal Geographical Society; thank you very much all of you for coming; and in particularly to the supporters of the Global Heritage Fund who stayed with us throughout all these years, and we hope to see you at the next [...] Thanks.

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