0:00:05 > 0:00:09These are the remains of the medieval city of Angkor in Cambodia.
0:00:09 > 0:00:15Former capital of one of the world's greatest civilisations,
0:00:15 > 0:00:17and once the biggest city on Earth.
0:00:19 > 0:00:21In many respects, Angkor is unique.
0:00:21 > 0:00:24The things that were achieved here were unparalleled
0:00:24 > 0:00:25throughout all of human history.
0:00:28 > 0:00:31Grand temples like Angkor Wat.
0:00:35 > 0:00:37Massive engineering projects.
0:00:41 > 0:00:44And huge reservoirs.
0:00:48 > 0:00:53This was once a vast city teeming with life.
0:00:54 > 0:00:58One has to really stop and be in awe of what has taken place here.
0:01:00 > 0:01:06Explorers and archaeologists have been coming here for over 150 years
0:01:06 > 0:01:10to find out about the people who built Angkor,
0:01:10 > 0:01:15and to try to discover why they abandoned the city.
0:01:17 > 0:01:19HORN TOOTS
0:01:26 > 0:01:30Now, archaeologists are using a sophisticated mapping technology
0:01:30 > 0:01:33called LiDAR to help solve the mystery of what happened here.
0:01:35 > 0:01:39By revealing a lost world beneath the trees,
0:01:39 > 0:01:43they allow us to imagine how the great city of Angkor once looked.
0:01:43 > 0:01:46LiDAR is an incredibly valuable tool because what it allows us to do
0:01:46 > 0:01:50is to breathe life back into this landscape.
0:01:50 > 0:01:55By unlocking the secrets of how this medieval metropolis flourished,
0:01:55 > 0:01:59they're also shedding new light on the dramatic events
0:01:59 > 0:02:00leading to its fall.
0:02:00 > 0:02:03That's what we describe as a one-two punch, and I think that was
0:02:03 > 0:02:07really the part where they realised things started to go horribly wrong.
0:02:09 > 0:02:12This new technology has revolutionised archaeology.
0:02:14 > 0:02:19And it helps to explain why the world's greatest medieval metropolis
0:02:19 > 0:02:20was abandoned to the jungle.
0:02:38 > 0:02:39800 years ago,
0:02:39 > 0:02:43a vast city flourished here in the Cambodian jungle.
0:02:44 > 0:02:47Angkor was the capital of the Khmer empire.
0:02:49 > 0:02:51By the end of the 12th century,
0:02:51 > 0:02:54the Khmer people had dominated south-east Asia
0:02:54 > 0:02:55for hundreds of years.
0:02:58 > 0:03:00The jewel in Angkor's crown,
0:03:00 > 0:03:04Angkor Wat,
0:03:04 > 0:03:07the biggest religious complex on Earth.
0:03:10 > 0:03:13But the story of Angkor and its people
0:03:13 > 0:03:16didn't end with the completion of this great temple.
0:03:21 > 0:03:2540 years later, and one kilometre to the north,
0:03:25 > 0:03:29construction began here at a new site called Angkor Thom.
0:03:31 > 0:03:34Its walls and moat are over 12 kilometres long.
0:03:39 > 0:03:43They enclose an area three times larger than medieval London.
0:03:46 > 0:03:50Angkor Thom would become the new seat of imperial power,
0:03:50 > 0:03:53a symbol of Angkor's golden age.
0:03:58 > 0:04:02Archaeologists have been studying this great royal enclosure
0:04:02 > 0:04:03for over a century.
0:04:05 > 0:04:09But the world of the people who lived here and beyond its walls
0:04:09 > 0:04:11largely remains a mystery.
0:04:13 > 0:04:18Dr Damian Evans is now trying to reveal the city's secrets.
0:04:19 > 0:04:22800 years ago, we would have been standing in the middle
0:04:22 > 0:04:25of a vast city, teeming with life.
0:04:25 > 0:04:28Unfortunately, almost all of that city was made of non-durable
0:04:28 > 0:04:32materials like wood and thatch, and has completely rotted away.
0:04:32 > 0:04:34The stuff that's remaining,
0:04:34 > 0:04:37the huge temples, this wall that we're standing on,
0:04:37 > 0:04:41is a very small and unrepresentative part of the whole city of Angkor.
0:04:41 > 0:04:45So this is the fundamental challenge that we're now trying to address,
0:04:45 > 0:04:48to try and reintroduce people into this landscape
0:04:48 > 0:04:51and understand it as a living city, as a lived-in space,
0:04:51 > 0:04:55rather than just a collection of empty and abandoned monuments.
0:04:56 > 0:04:59The new technology is called LiDAR.
0:04:59 > 0:05:03It's now being used to reveal the lost world beyond the temples.
0:05:08 > 0:05:12LiDAR works by firing laser beams through the foliage
0:05:12 > 0:05:15to measure the elevation of the land surface beneath.
0:05:17 > 0:05:20Billions of data points are captured,
0:05:20 > 0:05:24creating a ghostly outline of the medieval city.
0:05:29 > 0:05:34This LiDAR map gives archaeologists a revolutionary new way
0:05:34 > 0:05:37of investigating the history of Angkor.
0:05:41 > 0:05:45Some of LiDAR's biggest revelations lie beneath the jungle
0:05:45 > 0:05:47beyond the great moat of Angkor Thom.
0:05:50 > 0:05:53With the tree cover removed,
0:05:53 > 0:05:57LiDAR reveals the outline of a grid of city streets
0:05:57 > 0:05:59stretching into the distance.
0:06:01 > 0:06:04It allows us to build a graphic reconstruction
0:06:04 > 0:06:07revealing the scale of Angkor in its golden age.
0:06:12 > 0:06:19A formally planned metropolis, with tens of thousands of houses.
0:06:19 > 0:06:22Over three-quarters of a million people lived and worked
0:06:22 > 0:06:25in this bustling city all around the stone temples.
0:06:31 > 0:06:34The LiDAR data really transforms our vision of Angkor
0:06:34 > 0:06:35as a lived-in space.
0:06:38 > 0:06:40What it shows us is that this downtown area spread
0:06:40 > 0:06:42far into the landscape beyond,
0:06:42 > 0:06:46and also was accompanied by this huge network of infrastructure
0:06:46 > 0:06:51of roadways, of canals, of neighbourhoods that tied
0:06:51 > 0:06:55these far-flung areas of Angkor into the city centre where we are now.
0:06:58 > 0:07:00By the end of the 12th century,
0:07:00 > 0:07:04Angkor was one of the most sophisticated cities in the world.
0:07:06 > 0:07:09The LiDAR survey reveals the complexity
0:07:09 > 0:07:12of its vast water management network.
0:07:13 > 0:07:16At the heart of the system were massive reservoirs
0:07:16 > 0:07:19to store water from the annual monsoon.
0:07:21 > 0:07:23In dry years,
0:07:23 > 0:07:27this network was a lifeline for hundreds of thousands of people.
0:07:28 > 0:07:32In wet years, it helped control the flow of floodwater through the city.
0:07:35 > 0:07:38By the time Angkor Thom was built,
0:07:38 > 0:07:41the Khmer were masters of their environment.
0:07:41 > 0:07:44And their power and ambition was made clear
0:07:44 > 0:07:46in a new temple at its heart.
0:07:48 > 0:07:49The Bayon.
0:07:57 > 0:08:01Construction began on the Bayon towards the end of the 12th century.
0:08:01 > 0:08:05It was commissioned by the same monarch who built Angkor Thom's
0:08:05 > 0:08:07imposing walls,
0:08:07 > 0:08:12Jayavarman VII, one of the greatest Khmer kings.
0:08:15 > 0:08:19Professor Roland Fletcher is using the LiDAR data in his study
0:08:19 > 0:08:21of the rise and fall of Angkor.
0:08:23 > 0:08:27Jayavarman VII plays a pivotal role in the story.
0:08:29 > 0:08:35This immensity of Jayavarman VII's temple illustrates his significance.
0:08:35 > 0:08:39He, in a sense, epitomises everything that the Khmer world has been doing.
0:08:41 > 0:08:45Khmer kings had been building stone temples for hundreds of years.
0:08:49 > 0:08:54But Jayavarman VII now took Khmer temple building to a new level.
0:08:54 > 0:08:59The significance of Jayavarman VII is that he builds as many major temples
0:08:59 > 0:09:03as have been built in the preceding history of Angkor.
0:09:03 > 0:09:07So this is an absolutely tremendous building programme.
0:09:08 > 0:09:13The Bayon was this great king's statement of power and authority.
0:09:17 > 0:09:21The conventional view, and I think it's a reasonable one,
0:09:21 > 0:09:24is that these faces are the faces of Jayavarman VII.
0:09:24 > 0:09:28They are the profound representation of what he is doing.
0:09:29 > 0:09:32The faces look out in every direction across the city
0:09:32 > 0:09:34and across the empire.
0:09:41 > 0:09:45Today, the stone faces stare across a vast expanse of jungle.
0:09:49 > 0:09:53The LiDAR survey reveals the original view of the city.
0:10:01 > 0:10:05Little now remains of the bustling metropolis around the Bayon.
0:10:12 > 0:10:15But, on the walls of the temple itself, the lives of the people
0:10:15 > 0:10:20who lived here during the reign of Jayavarman VII can still be seen.
0:10:26 > 0:10:30Dr Julia Esteve lives here in Cambodia.
0:10:32 > 0:10:36She's spent 12 years studying life in Angkor at its peak.
0:10:56 > 0:10:58It's really lovely to be here at night
0:10:58 > 0:11:01and to be all alone in the temple.
0:11:01 > 0:11:05I can take the time to look at the everything, look at the bas-relief.
0:11:05 > 0:11:08I can even touch it, even though I'm not supposed to.
0:11:08 > 0:11:11And, yeah, it's really quite magic, I have to say.
0:11:16 > 0:11:20The carvings run for over half-a-kilometre around the temple.
0:11:24 > 0:11:27There are over 300 separate scenes
0:11:27 > 0:11:30with thousands of meticulously sculpted figures.
0:11:33 > 0:11:39Few representations of ordinary Khmer life survive in other temples.
0:11:40 > 0:11:42The bas-reliefs of the Bayon are very special
0:11:42 > 0:11:47because they give us a window on the daily life of the Khmer people
0:11:47 > 0:11:49at the end of the 12th century.
0:11:57 > 0:12:00From farmers to fishmongers,
0:12:00 > 0:12:02these carvings reveal the pattern of everyday life
0:12:02 > 0:12:04in the golden age of Angkor.
0:12:07 > 0:12:10The Khmer enjoyed games and gambling.
0:12:10 > 0:12:14Cock fighting seems especially popular.
0:12:14 > 0:12:17The carving we see here is particularly interesting
0:12:17 > 0:12:22for comparisons with daily life nowadays.
0:12:22 > 0:12:24In fact, we see preparation for a banquet
0:12:24 > 0:12:28and, er...we see a lot of, er...food being cooked.
0:12:28 > 0:12:32For example, a pig here held by two men
0:12:32 > 0:12:36is about to be put in boiled water in a cauldron.
0:12:36 > 0:12:39Maybe to skin it, or just to boil it.
0:12:39 > 0:12:43Over there, we have also a lot of people holding little cups,
0:12:43 > 0:12:46we can assume of rice wine.
0:12:46 > 0:12:48And it seems to be a time of peace.
0:12:48 > 0:12:51And it fits well with the idea we have of Jayavarman VII's reign.
0:12:52 > 0:12:54But the carvings also reveal this
0:12:54 > 0:12:57to be a land of dynastic rivalries and conflict.
0:13:09 > 0:13:13Large parts of the Bayon are covered with images of war.
0:13:15 > 0:13:20They record a bloody battle between two Khmer armies.
0:13:20 > 0:13:25Jayavarman VII comes to power in a very unpleasant civil war.
0:13:25 > 0:13:27He clearly is opposed by
0:13:27 > 0:13:31a significant portion of the Khmer elite.
0:13:31 > 0:13:36And this is a violent enough and unpleasant enough phenomenon
0:13:36 > 0:13:39that he portrays the defeat of a Khmer army
0:13:39 > 0:13:40on the walls of the Bayon.
0:13:43 > 0:13:46Essentially, this is a method of putting in stone,
0:13:46 > 0:13:48"I'm not going to forget,
0:13:48 > 0:13:50"my descendants are not going to forget."
0:13:50 > 0:13:52This was a vicious war.
0:13:54 > 0:13:57Having won the crown, this great warrior-king
0:13:57 > 0:14:00now unleashed a religious revolution.
0:14:02 > 0:14:06Jayavarman VII is not only a great military leader,
0:14:06 > 0:14:10he also introduces a major religious change
0:14:10 > 0:14:13in the form of making Mahayana Buddhism
0:14:13 > 0:14:15the primary religion of the state.
0:14:27 > 0:14:28FAINT CHANTING
0:14:30 > 0:14:34Today, Buddhism is the state religion of Cambodia.
0:14:37 > 0:14:41It is practised by more than 95% of the population.
0:14:46 > 0:14:50But before Jayavarman VII claimed the throne,
0:14:50 > 0:14:54Angkor's kings had been almost exclusively Hindu.
0:14:55 > 0:14:58Their legacy seen in monuments like Angkor Wat.
0:15:07 > 0:15:11Jayavarman VII was now using religious reformation
0:15:11 > 0:15:13as a tool to consolidate his power.
0:15:20 > 0:15:22The key thing that Jayavarman VII is doing
0:15:22 > 0:15:25is he's removing the preceding great families
0:15:25 > 0:15:30who controlled that enormous Hindu religious system.
0:15:30 > 0:15:32And they vanished from the record.
0:15:32 > 0:15:35And a new story starts with Jayavarman VII.
0:15:39 > 0:15:42In 1181, Jayavarman VII began
0:15:42 > 0:15:45the biggest building programme in Angkor's history.
0:15:47 > 0:15:50During his reign, he would pour the empire's resources
0:15:50 > 0:15:53into the construction of major stone temples and shrines
0:15:53 > 0:15:54throughout the city.
0:15:58 > 0:16:02One of the biggest lies just beyond the walls of Angkor Thom.
0:16:06 > 0:16:07Preah Khan.
0:16:10 > 0:16:14Preah Khan means sacred sword in Khmer.
0:16:14 > 0:16:19It was built in 1191 on the site of one of Jayavarman VII's
0:16:19 > 0:16:21greatest battlefield victories.
0:16:36 > 0:16:39Like many Khmer temples, Preah Khan was a centre
0:16:39 > 0:16:41of administrative and financial power,
0:16:41 > 0:16:45as well as a monastery and a place of learning.
0:16:45 > 0:16:49Tax levied here on Angkor's rice farmers went directly to the king.
0:16:52 > 0:16:53As the city prospered,
0:16:53 > 0:16:57Jayavarman VII's temples became fabulously wealthy.
0:17:00 > 0:17:04A 12th-century inscription suggests that 60 tons of gold
0:17:04 > 0:17:06once lined the walls of this central shrine.
0:17:17 > 0:17:21It's thought that these holes were used to support the panels of gold.
0:17:32 > 0:17:37Its value today would be about £2 billion.
0:17:51 > 0:17:54Much of the temple has been destroyed by the jungle.
0:17:57 > 0:18:00Preventing the trees from causing further damage
0:18:00 > 0:18:04is a major task for architectural conservator Glenn Boornazian.
0:18:08 > 0:18:14What we're seeing here is a seed that fell one day.
0:18:14 > 0:18:16It started to grow and no-one moved it.
0:18:16 > 0:18:20And then in the end, we end up with an object,
0:18:20 > 0:18:22or, you know, almost a being, like this.
0:18:22 > 0:18:25It almost looks like an alien that has come down
0:18:25 > 0:18:28and has grabbed onto all aspects of the masonry.
0:18:36 > 0:18:41Quite frankly, this will destroy this section of the building.
0:19:11 > 0:19:14We've got probably millions of stones here.
0:19:16 > 0:19:19And when we think about what the labour and the craft
0:19:19 > 0:19:24and the time that went into the construction of just one stone,
0:19:24 > 0:19:28it then helps us understand the amazing effort
0:19:28 > 0:19:30that took place at that time
0:19:30 > 0:19:33to create an incredible site like this.
0:19:39 > 0:19:40Glenn's conservation team
0:19:40 > 0:19:45has spent over 20 years working to preserve Preah Khan.
0:19:45 > 0:19:49If this is the top of the stone, it has to be a channel, like that.
0:19:49 > 0:19:51And then the cable drops in there.
0:19:53 > 0:19:56Today, they're at work on one of the four gateways
0:19:56 > 0:19:59to the main temple, the East Gopura.
0:20:05 > 0:20:08We are moving probably one of the largest stones
0:20:08 > 0:20:11that make up the central tower here on the East Gopura.
0:20:11 > 0:20:14It's about 2.3, 2.4 metres long
0:20:14 > 0:20:17and probably well over a ton in weight.
0:20:17 > 0:20:20So the amount of energy that it takes us to move it
0:20:20 > 0:20:23is...is...is extreme.
0:20:30 > 0:20:34What it makes me think is, OK, we're doing this here in 2014
0:20:34 > 0:20:36and we have some really, er...you know,
0:20:36 > 0:20:38I wouldn't call it state-of-the-art equipment,
0:20:38 > 0:20:42but certainly equipment that makes it easy to move this sized material.
0:20:42 > 0:20:44And then, if again, if I sort of close my eyes and wonder
0:20:44 > 0:20:50how Jayavarman VII and his team in the 1190s
0:20:50 > 0:20:54was also moving these stones, it's quite a wonder.
0:20:54 > 0:20:56I really can't comprehend that.
0:21:03 > 0:21:06The efforts of Jayavarman VII's workers
0:21:06 > 0:21:08are recorded in the Bayon carvings.
0:21:09 > 0:21:13They reveal that only the most basic tools were available.
0:21:14 > 0:21:17Labourers haul rocks with ropes.
0:21:17 > 0:21:22Others use wooden hoists to lower finished blocks into position.
0:21:23 > 0:21:26One of the more exciting and wonderful things that happens here
0:21:26 > 0:21:30when you're working on an ancient temple and you start to move a stone,
0:21:30 > 0:21:33I think one of the things that goes through your mind is,
0:21:33 > 0:21:37when was that stone last moved and who actually moved it?
0:21:37 > 0:21:39And if you think about that,
0:21:39 > 0:21:42you realise that the last time that stone was moved
0:21:42 > 0:21:45was in Jayavarman VII's time.
0:21:47 > 0:21:49And it does give you goose bumps.
0:21:54 > 0:21:58The labour required to move a single block gives an idea
0:21:58 > 0:22:02of the speed and efficiency of Jayavarman VII's workers.
0:22:03 > 0:22:07This effort was multiplied at vast temple sites throughout the city.
0:22:13 > 0:22:17The LiDAR map shows the position of Jayavarman VII's temples.
0:22:19 > 0:22:24In Angkor, houses of stone were reserved for the gods.
0:22:24 > 0:22:27Everyone else lived in homes made from wood or thatch.
0:22:27 > 0:22:30Including the king himself.
0:22:31 > 0:22:35Only the ghostly footprint of these lost buildings remains.
0:22:38 > 0:22:40But one vivid first-hand account
0:22:40 > 0:22:44of life around the temples still survives.
0:23:00 > 0:23:04At the lowest level come the homes of the common people.
0:23:04 > 0:23:08They only use thatch for their roofs
0:23:08 > 0:23:11and dare not put up a single tile.
0:23:13 > 0:23:15Although the sizes of their homes vary
0:23:15 > 0:23:18according to how wealthy they are,
0:23:18 > 0:23:23in the end, they do not dare emulate the styles of the great houses.
0:23:25 > 0:23:28These are the words of Zhou Daguan, a Chinese envoy
0:23:28 > 0:23:33who came to live in the city for nearly a year from 1296.
0:23:34 > 0:23:38His journal is a detailed and intimate record of life in Angkor.
0:23:40 > 0:23:43In this country, you can go without clothes.
0:23:46 > 0:23:48Food and women are easy to come by.
0:23:51 > 0:23:55Housing is easy to deal with.
0:23:55 > 0:23:59And it is easy to make do with a few essentials.
0:24:04 > 0:24:08With its reservoirs, fertile paddies and bustling streets,
0:24:08 > 0:24:10this was a land of plenty.
0:24:12 > 0:24:15But to sustain his temple-building programme,
0:24:15 > 0:24:19Jayavarman VII needed stone in ever-greater quantities.
0:24:31 > 0:24:33The LiDAR survey revealed the outline
0:24:33 > 0:24:36of some of the Khmer quarries.
0:24:36 > 0:24:39Damian is heading out to explore.
0:24:40 > 0:24:43Travelling with him is Simon Warrack,
0:24:43 > 0:24:45an expert in medieval stonemasonry.
0:24:58 > 0:25:00It's actually really nice to drive out here.
0:25:00 > 0:25:02It's beautiful countryside and very scenic.
0:25:04 > 0:25:07You never know what's going to come at you out of those trees.
0:25:09 > 0:25:12You just have to, er...keep your wits about you
0:25:12 > 0:25:14and expect anything at any time from any direction.
0:25:20 > 0:25:23The quarries lie around 40 kilometres
0:25:23 > 0:25:26north of Angkor's main temples.
0:25:28 > 0:25:30Transporting vast quantities of stone
0:25:30 > 0:25:32would have been a major challenge.
0:25:34 > 0:25:37The Bayon Temple is around 600,000 blocks,
0:25:37 > 0:25:40but the one thing that you have to bear in mind,
0:25:40 > 0:25:44on average, when you're cutting stone, there's at least 30% wastage.
0:25:44 > 0:25:48So you're bringing down large blocks.
0:25:48 > 0:25:5230% of which gets chipped off and ends up, er...in the floor
0:25:52 > 0:25:55for the archaeologists later on.
0:25:55 > 0:25:57It's massive. It's absolutely massive.
0:26:04 > 0:26:07Getting to the medieval Khmer quarries today
0:26:07 > 0:26:09is a challenge in itself.
0:26:11 > 0:26:13We're 4Ks away.
0:26:13 > 0:26:17- Still?- Yeah.
0:26:17 > 0:26:21The road runs out. And Damian and Simon have to walk.
0:26:26 > 0:26:30Yeah. If there's any path that goes right, we need to swing right.
0:26:30 > 0:26:33They have to pick their path carefully.
0:26:33 > 0:26:39From the 1960s to 1990s, Cambodia was torn by conflict and war.
0:26:39 > 0:26:42Land mines remain an ever-present danger.
0:26:43 > 0:26:46Mind you, this is all fine. It's been cultivated,
0:26:46 > 0:26:49so land mines are not too much of a worry.
0:26:49 > 0:26:52But it's not long before the track runs out.
0:26:55 > 0:26:58What we're going to have to do is to go bush bashing
0:26:58 > 0:27:00at this point, basically,
0:27:00 > 0:27:03which is not normally the best idea in an area that's well known
0:27:03 > 0:27:05for having a lot of land mines.
0:27:05 > 0:27:08Fortunately, there's a gentleman here who apparently knows a way.
0:27:08 > 0:27:12Even if there's no path, we can kind of walk through cultivated areas,
0:27:12 > 0:27:14which, er, should be safe.
0:27:14 > 0:27:17And he reckons he can take us to those particular quarries
0:27:17 > 0:27:19that we're interested in.
0:27:23 > 0:27:26The local farmer leads them across the dry paddy fields
0:27:26 > 0:27:28to a safe path through a village.
0:27:32 > 0:27:36From here, Damian and Simon can carry on without assistance.
0:27:45 > 0:27:48Soon, they see signs of quarrying.
0:27:57 > 0:28:00- This is big.- All the way around here...!- This is really big.
0:28:00 > 0:28:02One big, huge ridge. It's amazing.
0:28:13 > 0:28:15Yeah, it's beautiful, isn't it?
0:28:15 > 0:28:17You can really see the chisel marks there
0:28:17 > 0:28:18and the stepping of the stones.
0:28:20 > 0:28:24It's incredibly silent out here, isn't it, in the middle of nowhere?
0:28:24 > 0:28:27You can just imagine 800 years ago,
0:28:27 > 0:28:29there would have been thousands upon thousands of people
0:28:29 > 0:28:33chipping away at sandstone with iron chisels in this area.
0:28:33 > 0:28:36I mean, even the sound must have been incredible.
0:28:37 > 0:28:40I would imagine that they were probably working in teams.
0:28:40 > 0:28:42Do you think they would get paid per block
0:28:42 > 0:28:44or do you think they were just told to go and...?
0:28:44 > 0:28:47My personal opinion is that people would have been rounded up
0:28:47 > 0:28:50- and pretty much forced to do this kind of work.- Yeah.
0:28:50 > 0:28:53It has to have been an incredibly difficult, difficult job.
0:28:53 > 0:28:56And really unsafe out here, as well.
0:28:56 > 0:29:01I doubt it was safety first in the 12th century!
0:29:03 > 0:29:05The labourers would have lived on a simple diet
0:29:05 > 0:29:07of rice and fermented fish paste.
0:29:08 > 0:29:11They removed thousands of blocks from this site.
0:29:14 > 0:29:16Archaeologists once thought
0:29:16 > 0:29:18there used to be many small quarries in the region.
0:29:20 > 0:29:22But LiDAR has now changed this view.
0:29:24 > 0:29:26When you have exposed bits like this, outcrops,
0:29:26 > 0:29:30it's very easy to see evidence of quarrying.
0:29:30 > 0:29:33The problem is that the quarries weren't always on bits
0:29:33 > 0:29:35that stuck out of the ground like this.
0:29:35 > 0:29:37Quite often, they were in pits dug into the ground.
0:29:37 > 0:29:39And those have filled in centuries ago.
0:29:40 > 0:29:44What the LiDAR can do is it can show us the depressions
0:29:44 > 0:29:47that are basically the remains of those in-filled pits.
0:29:47 > 0:29:49And using that new information, we can see that
0:29:49 > 0:29:52we're looking at a single, vast quarry field, in fact.
0:29:56 > 0:29:58The LiDAR survey reveals many areas
0:29:58 > 0:30:01where previously-unknown quarrying took place.
0:30:02 > 0:30:06This is the source of many of the estimated five million blocks
0:30:06 > 0:30:07in Angkor's temples.
0:30:09 > 0:30:14The new map also reveals how so much stone was transported.
0:30:17 > 0:30:19It shows canals stretching back to the city.
0:30:23 > 0:30:27Blocks were floated to Jayavarman VII's building sites on rafts.
0:30:33 > 0:30:36With a steady flow of stone from the quarries,
0:30:36 > 0:30:39Angkor continued to expand and flourish.
0:30:47 > 0:30:52When Chinese traveller Zhou Daguan arrived in 1296,
0:30:52 > 0:30:55he was impressed by the vibrant metropolis.
0:31:00 > 0:31:02There is a market every day
0:31:02 > 0:31:05from around six in the morning until midday.
0:31:08 > 0:31:12Small market transactions are paid for with some rice
0:31:12 > 0:31:14or other grain and Chinese goods.
0:31:18 > 0:31:22The ones next up in size are paid for with cloth.
0:31:22 > 0:31:26Large transactions are done with gold and silver.
0:31:28 > 0:31:32Zhou Daguan's journal reveals his interest in Angkor's markets.
0:31:33 > 0:31:37It's possible he was sent to gather commercial information
0:31:37 > 0:31:40about one of the most successful economies in Asia.
0:31:41 > 0:31:44He records a wealth of produce
0:31:44 > 0:31:46and an abundance of fresh fish.
0:31:52 > 0:31:56But the foundation for the city's wealth was agriculture.
0:31:56 > 0:32:00Its fields kept lush by the sophisticated management
0:32:00 > 0:32:02of water from the annual monsoon.
0:32:05 > 0:32:10In general, crops can be harvested three or four times a year.
0:32:10 > 0:32:12The reason being that all four seasons
0:32:12 > 0:32:15are like our fifth and sixth months,
0:32:15 > 0:32:18with days that know no frost or snow.
0:32:19 > 0:32:22For six months, the land has rain.
0:32:22 > 0:32:24For six months, no rain at all.
0:32:28 > 0:32:30The staple crop was rice.
0:32:33 > 0:32:36The expanding city was built around the paddy fields.
0:33:00 > 0:33:05By the end of the 13th century, Angkor was a sprawling metropolis.
0:33:06 > 0:33:09The LiDAR survey led by Dr Damian Evans
0:33:09 > 0:33:11has covered only a fraction of the city.
0:33:19 > 0:33:22Almost 250 square kilometres of Angkor
0:33:22 > 0:33:25have been mapped with LiDAR so far.
0:33:27 > 0:33:31This is where the major state temples are located.
0:33:31 > 0:33:34But the urban sprawl continued much further
0:33:34 > 0:33:36into the surrounding landscape.
0:33:39 > 0:33:42It's a long ride from the centre of Angkor
0:33:42 > 0:33:44to the city's medieval outskirts.
0:33:45 > 0:33:48With nearly 20 kilometres on the clock,
0:33:48 > 0:33:52Damian is now well beyond the area covered by the LiDAR survey.
0:33:55 > 0:33:58A first glance reveals few clues
0:33:58 > 0:34:02that these outlying areas would once have been part of the city.
0:34:03 > 0:34:06But some historic landscape features survive.
0:34:06 > 0:34:09Because we've gone off the edge of the LiDAR map,
0:34:09 > 0:34:12what I'm looking at here is mapping data that we acquired
0:34:12 > 0:34:15several years ago from aerial photographs alone.
0:34:15 > 0:34:18We can clearly see that there's an enormous square enclosure here.
0:34:20 > 0:34:23The enclosure of Banteay Srei lies 20 kilometres
0:34:23 > 0:34:25from the centre of the city.
0:34:27 > 0:34:30It's evidence of Angkor's extraordinary expansion.
0:34:33 > 0:34:35One of the interesting things about Angkor
0:34:35 > 0:34:37is that in terms of its size and scale,
0:34:37 > 0:34:40it's comparable to these mega cities that have developed
0:34:40 > 0:34:42over the course of the 20th century.
0:34:45 > 0:34:48Banteay Srei is one of many historic sites
0:34:48 > 0:34:51found in areas away from the city centre.
0:34:55 > 0:34:59They spread far beyond the area of LiDAR coverage
0:34:59 > 0:35:01in the heart of the city.
0:35:04 > 0:35:08These outlying sites show that Angkor's great urban sprawl
0:35:08 > 0:35:11once covered 1,000 square kilometres.
0:35:14 > 0:35:16It would be another 700 years
0:35:16 > 0:35:20before London stole its crown as the largest city on earth.
0:35:24 > 0:35:26Archaeologists are unsure
0:35:26 > 0:35:29what the enclosure of Banteay Srei was used for.
0:35:30 > 0:35:34But information from the LiDAR survey elsewhere in the city
0:35:34 > 0:35:38helps create an image of how its moat might once have looked.
0:35:41 > 0:35:44During the time that this place was built and inhabited,
0:35:44 > 0:35:47you wouldn't have had really any of this vegetation around
0:35:47 > 0:35:50and the banks of this particular moat here
0:35:50 > 0:35:52would've been populated with wooden houses.
0:35:52 > 0:35:55So you would've seen communities on stilted houses
0:35:55 > 0:35:58arrayed along the banks of this particular moat.
0:36:02 > 0:36:03In fact, Zhou Daguan,
0:36:03 > 0:36:06when he visited here at the end of the 13th century, described
0:36:06 > 0:36:10a system of residence where people lived along the banks of ponds.
0:36:10 > 0:36:13And, of course, we can see the remnants of
0:36:13 > 0:36:15those features here today.
0:36:16 > 0:36:19The place is unbearably hot,
0:36:19 > 0:36:22and no-one can go without bathing several times a day.
0:36:24 > 0:36:28Even at night you have to bathe once or twice.
0:36:31 > 0:36:35They may never have had bathrooms, but every family is sure to
0:36:35 > 0:36:40have a pond, or at least a pond to share among two or three families.
0:36:46 > 0:36:48The LiDAR survey reveals
0:36:48 > 0:36:50over 4,500 ponds
0:36:50 > 0:36:53across the centre of the city.
0:36:53 > 0:36:57By mapping them, archaeologists can identify dense clusters
0:36:57 > 0:37:02of population in long-forgotten neighbourhoods beyond the temples.
0:37:06 > 0:37:09So we've moved, in just a few short years, from a picture
0:37:09 > 0:37:14of Angkor as just a collection of cold, grey, stone temples
0:37:14 > 0:37:17to a much more nuanced and much more sophisticated picture of Angkor.
0:37:17 > 0:37:22As a lived-in space, a vibrant space full of humans and activity.
0:37:26 > 0:37:30Jayavarman VII used the vast resources of this flourishing city
0:37:30 > 0:37:33to construct his many temples and shrines.
0:37:36 > 0:37:40But the resources required to maintain them were even greater.
0:37:50 > 0:37:52Evidence for this can be found
0:37:52 > 0:37:55in the Cambodian Ministry of Culture's warehouse.
0:38:01 > 0:38:05Monumental standing stone slabs known as stele.
0:38:08 > 0:38:12Carved with inscriptions recording how the temples were managed.
0:38:13 > 0:38:16This one is from Preah Khan.
0:38:17 > 0:38:21The stele that you see here is essentially a record of the assets
0:38:21 > 0:38:23of the temple.
0:38:23 > 0:38:26It lists the number of villages that are indented to the temple,
0:38:26 > 0:38:30the workforce, the events that are occurring,
0:38:30 > 0:38:32supplies that have to be delivered.
0:38:32 > 0:38:37This text, written in Sanskrit poetry, reveals the huge
0:38:37 > 0:38:40numbers of people required to keep Preah Khan running.
0:38:42 > 0:38:48In the Ta Prohm temple stele, you have a really remarkable record.
0:38:48 > 0:38:53You are told that 12,640 people worked for this temple.
0:38:53 > 0:38:54Gives you some idea of the scale.
0:38:54 > 0:39:00There are 615 dancers, which is a very large dance troupe.
0:39:00 > 0:39:03You have over 2,000 administrators,
0:39:03 > 0:39:09you have somewhere between 1,000 and 2,000 teachers and their students.
0:39:09 > 0:39:11So, you have a very elaborate administration,
0:39:11 > 0:39:15of which you're only seeing a fraction mentioned.
0:39:17 > 0:39:21The LiDAR map has revealed where thousands of temple staff
0:39:21 > 0:39:24once lived in the area around Ta Prohm temple.
0:39:30 > 0:39:34Feeding them all required the labour of 66,000 rice farmers
0:39:34 > 0:39:36in the surrounding fields.
0:39:41 > 0:39:44So, if you total up the number of people who support
0:39:44 > 0:39:49and work for the Preah Khan temple and the Ta Prohm,
0:39:49 > 0:39:54it's over 150,000 people, and that's two medium sized temples.
0:39:54 > 0:39:58When you start adding in the staff and the support for places
0:39:58 > 0:40:02like Angkor Wat, the numbers begin to seriously skyrocket.
0:40:07 > 0:40:09Jayavarman VII's building spree
0:40:09 > 0:40:12transformed the dynamics of city life.
0:40:16 > 0:40:20By the time the Bayon was completed, over half a million people
0:40:20 > 0:40:23were committed to maintaining the temples.
0:40:28 > 0:40:32The problem with this is that the majority of the population
0:40:32 > 0:40:37of greater Angkor is servicing and supplying the temples.
0:40:37 > 0:40:41It's sucking resources in all the time and
0:40:41 > 0:40:44what the growth of the temple system does is it boxes them in.
0:40:53 > 0:40:58Jayavarman VII died in 1218.
0:40:58 > 0:41:00Angkor's golden age was over.
0:41:02 > 0:41:06During his reign, his labourers had filled his city with temples.
0:41:08 > 0:41:11But only one new stone temple was commissioned here in the years
0:41:11 > 0:41:12that followed.
0:41:14 > 0:41:16The tiny Mangalartha temple
0:41:16 > 0:41:19was the last ever to be constructed in the city.
0:41:23 > 0:41:28Within decades of its completion in 1295,
0:41:28 > 0:41:31Angkor began its final spiral of decline.
0:41:35 > 0:41:39But there's more to the fall of Angkor than an over-ambitious king
0:41:39 > 0:41:42burdening his people with too many temples.
0:41:48 > 0:41:52Archaeologists now believe that the mystery of the city's decline
0:41:52 > 0:41:55can be explained by studying the infrastructure
0:41:55 > 0:41:57which allowed it to flourish.
0:42:03 > 0:42:07Angkor's success was built on its vast water network.
0:42:17 > 0:42:21The great reservoir known as The West Baray
0:42:21 > 0:42:24can hold up to 49 billion litres of water
0:42:24 > 0:42:27within its ten-metre-high earth banks.
0:42:36 > 0:42:39This reservoir was connected to the wider water network
0:42:39 > 0:42:43by an intricate system of canals and embankments.
0:42:45 > 0:42:49To the east of Angkor Thom, other large reservoirs also helped
0:42:49 > 0:42:52manage the flow of water across the city.
0:42:55 > 0:42:59For centuries, Angkor's water network gave its citizens
0:42:59 > 0:43:02food security and flood protection.
0:43:04 > 0:43:06But by the mid-13th century,
0:43:06 > 0:43:09the system was beginning to show signs of its age.
0:43:12 > 0:43:16Scientist Dan Penny has been investigating Angkor's
0:43:16 > 0:43:19mysterious decline for over a decade.
0:43:21 > 0:43:25By analysing medieval pollen samples, he's identified
0:43:25 > 0:43:29a dramatic change that occurred here soon after Jayavarman VII's death.
0:43:31 > 0:43:34We know that from the time this reservoir was built
0:43:34 > 0:43:36in the mid-11th century
0:43:36 > 0:43:39to the time immediately after Jayavarman VII,
0:43:39 > 0:43:41it held deep, clear standing water.
0:43:41 > 0:43:43And we know that because we find
0:43:43 > 0:43:46pollen grains in the sediment in the reservoir.
0:43:46 > 0:43:51Pollen grains like this, this is Nelumbo nucifera, the sacred lotus.
0:43:51 > 0:43:55And pollen from plants like this and a range of others indicate
0:43:55 > 0:43:58the water in this reservoir was quite high and was permanent.
0:43:59 > 0:44:04However, after the time of Jayavarman VII, we have a switch
0:44:04 > 0:44:08in the kind of plants which were growing here, from these, to
0:44:08 > 0:44:14pollen grains like these, which derive from fern spores and grasses.
0:44:14 > 0:44:17Which tell us that we've shifted from an open water reservoir
0:44:17 > 0:44:20to effectively a swamp or even to dry land.
0:44:21 > 0:44:23These pollen samples reveal
0:44:23 > 0:44:26the rapid drying-up of Angkor's reservoirs.
0:44:28 > 0:44:30This was a wealthy city.
0:44:30 > 0:44:34But centuries of adaptations to the increasingly complex water network
0:44:34 > 0:44:35were taking their toll.
0:44:38 > 0:44:42It's ironic, in a way, that even when Angkor was reaching its zenith
0:44:42 > 0:44:46its major pieces of water management infrastructure were failing
0:44:46 > 0:44:47and were falling into disrepair.
0:44:49 > 0:44:53The decline of this vital system would leave Angkor vulnerable
0:44:53 > 0:44:55to what came next.
0:44:57 > 0:44:59In the 14th century,
0:44:59 > 0:45:03Angkor's ageing water network received a devastating blow.
0:45:05 > 0:45:10Evidence for what happened can be found over 700 kilometres away
0:45:10 > 0:45:12in present-day Vietnam.
0:45:26 > 0:45:30The Lang Biang highlands rise over 2,000 metres.
0:45:37 > 0:45:40They are covered in ancient primary forest.
0:45:50 > 0:45:52Scientists working here...
0:45:53 > 0:45:57..are now finding a new explanation for Angkor's decline.
0:46:05 > 0:46:09We're up kind of high here. We're high elevation, it's mist forest
0:46:09 > 0:46:12but you start doing this, you'll warm right up.
0:46:18 > 0:46:22Dr Brendan Buckley and his colleagues are taking core samples
0:46:22 > 0:46:26from a rare species of pine unique to Vietnam's highlands.
0:46:28 > 0:46:32Pinus krempfii grow slowly in the chilly mountain air
0:46:32 > 0:46:34and can live 1,000 years.
0:46:37 > 0:46:41We've found Krempfii that are more than two metres in diameter.
0:46:41 > 0:46:43So this one is 1.5 metres.
0:46:43 > 0:46:46There are some that are a lot bigger than this.
0:46:53 > 0:46:55DRILLING SOUND
0:46:59 > 0:47:04This tree is big enough, and so old enough, to have been growing
0:47:04 > 0:47:06when Angkor flourished.
0:47:09 > 0:47:12Taking core samples doesn't harm the tree.
0:47:14 > 0:47:16That's probably about as far as I want to go in this core for now.
0:47:17 > 0:47:20I'm going to pull the core out. We use this spoon
0:47:20 > 0:47:23and it just slides in under the dowel of wood that I've cut
0:47:23 > 0:47:27and when I turn this back, it breaks the end of it off.
0:47:27 > 0:47:29So now I can just pull the core out.
0:47:36 > 0:47:38And that's, that's a beautiful core.
0:47:38 > 0:47:40Actually, this is a really...
0:47:40 > 0:47:42That's a really beautiful core, you see that?
0:47:46 > 0:47:48So, you can see all the rings through time.
0:47:52 > 0:47:55These rings reveal the annual climate throughout the tree's life.
0:47:58 > 0:48:00A wet year results in a wide ring.
0:48:04 > 0:48:07A narrow ring reveals a drought.
0:48:08 > 0:48:12We've captured the whole record of this tree's life,
0:48:12 > 0:48:15its story told year by year by the annual growth rings.
0:48:15 > 0:48:17It goes back about 800 years.
0:48:17 > 0:48:21Back to the period of time when the Angkor civilisation reached its end.
0:48:26 > 0:48:30By sampling trees all across south-east Asia,
0:48:30 > 0:48:32Brendan has revealed a dramatic
0:48:32 > 0:48:35sequence of events back in the 14th century.
0:48:49 > 0:48:53Good day of coring, gentlemen. Thank you for the work. Cheers.
0:48:53 > 0:48:54Cheers.
0:48:54 > 0:48:56- Yo.- Yo.
0:48:56 > 0:48:57THEY LAUGH
0:48:58 > 0:49:02The core samples collected today will be added to Brendan's
0:49:02 > 0:49:06database of over 1,000 from the region.
0:49:06 > 0:49:07But before we get too drunk,
0:49:07 > 0:49:10we should also take a look at those cores.
0:49:10 > 0:49:14Each one will be dried and mounted, like these samples from his lab.
0:49:15 > 0:49:18That tree has got to be a millennial,
0:49:18 > 0:49:19that's got to be 1,000 years old.
0:49:20 > 0:49:23There's probably 100 rings right there.
0:49:24 > 0:49:28They show that the highpoint of Khmer civilisation coincided
0:49:28 > 0:49:31with particularly favourable climate conditions.
0:49:33 > 0:49:36The Khmer built their civilisation on the kindest
0:49:36 > 0:49:39period of climate that we had in the last 1,000 years.
0:49:39 > 0:49:41They built their whole system
0:49:41 > 0:49:44based on the way the climate was at that time.
0:49:47 > 0:49:50But this period of stable climate was coming to an end.
0:49:52 > 0:49:55Coming out of that really nice period of climate,
0:49:55 > 0:49:57you really start to see this decline in the rainfall,
0:49:57 > 0:50:00and that shows up very clearly in the tree ring record.
0:50:04 > 0:50:07The rings in this period suddenly become much narrower.
0:50:13 > 0:50:16And remain narrow for over three decades.
0:50:18 > 0:50:20So when we go back and we see these big suppressions
0:50:20 > 0:50:24in the growth rings, we know that we have droughts that took place.
0:50:24 > 0:50:27And for them to last for decades like that, they
0:50:27 > 0:50:30have to be really significant failures of the monsoon.
0:50:33 > 0:50:36The failure of the monsoon would have placed a severe
0:50:36 > 0:50:38strain on the city's crumbling water network.
0:50:42 > 0:50:44But worse was to come.
0:50:44 > 0:50:47In the late 14th century,
0:50:47 > 0:50:50the tree rings become unusually wide.
0:50:52 > 0:50:56After decades of drought came a deluge.
0:51:00 > 0:51:02So, the Khmer period of decline
0:51:02 > 0:51:04really was a matter of a few decades
0:51:04 > 0:51:08that it went from extreme dry to extreme wet and then back again.
0:51:13 > 0:51:17That's sort of what we describe as a one-two punch.
0:51:17 > 0:51:19THUNDER RUMBLES
0:51:21 > 0:51:23So that, the wet period was something that was
0:51:23 > 0:51:26equally as bad, if not more so, than the droughts were.
0:51:26 > 0:51:28So not only do they get hit by drought,
0:51:28 > 0:51:30they get hit by massive amounts of water.
0:51:33 > 0:51:38Angkor's ageing water network now faced its greatest challenge.
0:51:55 > 0:51:58The Siem Reap river flows through the heart of Angkor.
0:52:02 > 0:52:05Dr Dan Penny believes that the changing climate
0:52:05 > 0:52:09here in the 14th century destroyed the city's water network.
0:52:16 > 0:52:20'Rivers in this kind of environment, very flat plain like this,'
0:52:20 > 0:52:24will tend to meander when they're left to their own devices.
0:52:24 > 0:52:27So when we see a straight stretch of water like this one
0:52:27 > 0:52:31we know for certain that it's artificial.
0:52:31 > 0:52:35This isn't a natural river but a medieval Khmer canal.
0:52:38 > 0:52:42On the LiDAR map, the canal can be seen to follow a straight
0:52:42 > 0:52:45course for over five kilometres.
0:52:45 > 0:52:48It was built during the time of drought to channel precious
0:52:48 > 0:52:51water directly into the city centre.
0:52:52 > 0:52:56But as the climate went from extreme dry to extreme wet,
0:52:56 > 0:53:00the construction of this canal proved to be a tragic mistake.
0:53:05 > 0:53:08So, this system was designed to carry a certain level of water.
0:53:08 > 0:53:13But if you put a very much larger volume of water through a straight
0:53:13 > 0:53:16channel like this, the potential for catastrophe is very high.
0:53:22 > 0:53:24The straighter a river, the faster it flows.
0:53:27 > 0:53:29And the deeper it will cut down into the riverbed.
0:53:33 > 0:53:35These high banks reveal that this happened here
0:53:35 > 0:53:38when the climate suddenly became much wetter.
0:53:40 > 0:53:43In places, floodwater here
0:53:43 > 0:53:47cut down nearly ten metres below the original land surface.
0:53:54 > 0:53:58The devastating effect of these floods on Angkor's infrastructure
0:53:58 > 0:53:59can be seen here.
0:54:01 > 0:54:05Spean Thma is one of the city's few surviving bridges.
0:54:07 > 0:54:10It now sits high above the old canal.
0:54:13 > 0:54:15If you'd stood where we are standing now
0:54:15 > 0:54:19perhaps in the 14th century, you would be standing in water
0:54:19 > 0:54:21and this would have been a flowing canal.
0:54:21 > 0:54:25The water now is almost ten metres below the bridge,
0:54:25 > 0:54:29and in fact has destroyed its eastern side, leaving
0:54:29 > 0:54:31the bridge hanging up the side of the valley.
0:54:34 > 0:54:37The LiDAR map shows the power of the floodwater.
0:54:40 > 0:54:44On meeting the stone bridge, it took the path of least resistance,
0:54:44 > 0:54:48swerving to carve down through the soft soil of the riverbank,
0:54:48 > 0:54:50before re-joining the canal.
0:54:52 > 0:54:54But this wasn't the only damage.
0:54:56 > 0:55:00LiDAR reveals that the swollen river also breached embankments...
0:55:03 > 0:55:05..and destroyed people's homes.
0:55:07 > 0:55:11Right across the city, crucial irrigation channels were left
0:55:11 > 0:55:14high and dry above the new level of the river.
0:55:16 > 0:55:19And sediment eroded from the riverbed was now washed
0:55:19 > 0:55:24downstream past Angkor Wat, and swamped the city's southern canals.
0:55:27 > 0:55:31Angkor's intricate water network would never recover.
0:55:40 > 0:55:42The destruction of the water management system was
0:55:42 > 0:55:47the specific trigger for Angkor's demise as a viable settlement.
0:55:49 > 0:55:52In fact, in many ways it was the scale of the city,
0:55:52 > 0:55:54and particularly its water network,
0:55:54 > 0:55:56'which was vast and complex
0:55:56 > 0:55:59'and deeply interconnected, that allowed this place to become
0:55:59 > 0:56:00'so vulnerable.'
0:56:00 > 0:56:05To the point at which this episode of climate variability occurred
0:56:05 > 0:56:08and effectively it completely destroyed the system.
0:56:12 > 0:56:16With its water network in tatters, the city's decline accelerated.
0:56:20 > 0:56:23But the Khmer civilisation itself didn't die.
0:56:26 > 0:56:30In the mid-15th century, the Khmer kings abandoned Angkor
0:56:30 > 0:56:34and moved the imperial administration towards the coast.
0:56:38 > 0:56:44They built a new city, Phnom Penh, the present-day capital of Cambodia.
0:56:51 > 0:56:53Angkor was slowly devoured by the jungle.
0:56:59 > 0:57:03But it never completely disappeared like the fabled Atlantis.
0:57:08 > 0:57:13Over the following centuries, most of the people simply moved away.
0:57:18 > 0:57:21By the time French explorers made Angkor's temples
0:57:21 > 0:57:25famous in the 1860s, little of the city could be seen.
0:57:28 > 0:57:32And the legend of a mysterious "lost civilisation" began to grow.
0:57:36 > 0:57:38But many of the temples had continued to
0:57:38 > 0:57:43function for hundreds of years, including the greatest of them all.
0:57:48 > 0:57:52Angkor Wat has been in constant use since the day it was built.
0:57:59 > 0:58:02Today, it's visited by millions of tourists.
0:58:05 > 0:58:09Now, with the help of LiDAR, we can see the lost city
0:58:09 > 0:58:11all around it once again.
0:58:12 > 0:58:16One of the greatest achievements in human history.
0:58:18 > 0:58:20The medieval metropolis of Angkor.