Angkor Wat's Hidden Megacity Jungle Atlantis

1,000 years ago, one of the world's greatest civilisations

built an empire here in Cambodia.

It dominated Southeast Asia for nearly 600 years...

..and was the biggest superpower the region has ever seen.

Their capital was the great city of Angkor.

This was an extensive kingdom.

Its power surpassed the modern-day borders,

an empire this great is something to be truly marvelled at

and to have so much remaining from that time,

it's just a remarkable thing to witness.

Starting as a nation of rice farmers,

the Khmer people would go on to build some of the most

spectacular structures of the Medieval age.

The pinnacle of their culture was the great temple Angkor Wat,

still the largest religious monument in the world.

But 500 years ago, the Khmer kings abandoned their capital.

The city of Angkor was quickly devoured by the jungle.

For over 100 years, scientists have been unable to explain why

one of the world's most powerful civilisations abandoned their city.

Now an international team of experts is trying to solve

one of the great mysteries of the Medieval age.

As archaeologists, we're interested in questions of, who the

people were who built these temples,

where do they come from? How did they survive?

What did their cities look like and what happened to them?

Using a revolutionary laser-scanning technique called LIDAR,

they're looking beneath the jungle to uncover the secrets of this

extraordinary civilisation.

This is the royal palace, the civil centre of that ancient city

where the king would live.

It's amazing. Really amazing.

For the first time in 500 years, LIDAR is helping to reveal

the lost metropolis of the people who built Angkor Wat.

Some colleagues of mine have described it as, essentially,

a scientific revolution.

We are now closer than ever before to

an understanding of how the Khmer people came to dominate

Southeast Asia and why their great city ultimately collapsed.

Deep inside the stone chambers of Angkor Wat,

the annual candle ceremony - Meak Bochea.

A Buddhist ceremony to purify the mind.

Many people think of Angkor Wat as a dead monument,

a place that was abandoned

and the tourists come here just to admire its architecture.

But, you know, it's a living monument.

It's a place which has real life in amongst the people of Cambodia.

It's an amazing place, a special place.

Angkor Wat is a place full of surprises.

Angkor Wat is one of the most beautiful and mysterious buildings

in the world.

Five huge towers shaped like lotus buds,

surrounded by a six-kilometre moat.

A temple of perfect symmetry covering an area

of two square kilometres.

This is one of the wonders of the Medieval world.

What I feel when I see Angkor Wat is, I am impressed

by the coming together,

the collectivity of a great many kinds of genius here.

The genius of the mathematician,

the genius of the artist, the genius of the architect,

the genius of the engineer and the genius of the people who

aspired to build these things.

Who cannot be in love with Angkor?

The temple was constructed nearly 1,000 years ago.

In Europe at that time,

the Normans would spend over 100 years building their

vast cathedrals.

The Khmer people completed Angkor Wat in under 40,

and that included 2km of intricate engravings with

nearly 2,000 celestial dancers from Hindu mythology,

every one unique.

In the 12th century, this was the spiritual and administrative

heart of the city of Angkor.

It would come to rule an empire

that stretched a million square kilometres across Southeast Asia.

Every year, more than two million people are drawn to the Khmer's

archaeological treasures.

They drive a tourist industry worth more than 2 billion a year,

nearly 20% of Cambodia's entire economy.

But the people who built this temple

and the city around it remain an enigma.

Most evidence for how the Khmer people built their city

has been lost or swallowed by the jungle.

Archaeologists and historians have been studying Angkor

for about 150, 160 years, but little was known

about the actual people who inhabited these spaces.

The great stone buildings were one thing,

but not everyone lived in the temples,

and so more and more throughout the 20th century

the questions were being asked, what about the everyday people?

Who were they? Where did they live? What was their life like?

Now a new project is attempting to solve some of these mysteries...

..by using a revolutionary technology called LIDAR.

We're airborne above Angkor.

Damian Evans, from the University of Sydney, is leading a team

of international experts who are peeling back the layers of forest

to reveal the secrets of the people who built Angkor Wat.

Most of the city that existed here 1,000 years ago

would have been made of very, very flimsy material.

Just light pieces of wood and thatch and so on.

Within one or two years, that stuff just rots away completely.

We can still make out these very, very subtle traces of where

they used to be, by analysing the surface topography of the landscape.

LIDAR works in a similar way to radar.

It scans the ground by sending out a million laser points

every four seconds and analysing the information reflected back.

The time it takes for each pulse to break through the trees,

hit the ground and return is measured.

The results are then mapped.

The shapes revealed are the footprints of structures

from the long-lost capital of the Angkorian empire.

We get this data back to the office, we can click a button,

strip those trees from the picture and really, for the first time,

see those cities of Angkor emerge in incredible detail

on the computer screen in front of us.

The jungle is removed in an instant.

The LIDAR data renders an outline of everything on the surface

of the land.

The glory of Angkor Wat becomes a ghostly outline of digital points.

But LIDAR also reveals the shape of the old city.

Angkor Wat is shown to be surrounded by the ghostly

outline of a vast metropolis.

And we can use this data to re-build the city of Angkor

as it would have looked over 900 years ago.

Shadowy lines that were once roads...

..canals long since swallowed by the jungle...

..and the outline of thousands of houses, monasteries and palaces.

It's an incredible leap forward for us to be able to use this technique.

You can imagine that doing things by hand on the ground

is a process that would take decades, basically.

Now, using these new techniques, we have the opportunity

to do a bit of flying, just a few hours, to take that data back to the

office and with a few clicks of the button, we see entire urban

landscapes unfolding on the screen in front of us for the first time.

The LIDAR imagery shows that central Angkor

was organised into regular-sized city blocks...

..and that many of the dwellings of the Angkorian era

were clustered around thousands of ponds.

LIDAR is an incredibly valuable tool,

because what it allows us to do is to breathe life back into that landscape.

For the first time, it reveals with exceptional clarity

these vanished cities that surrounded the monuments

and allows us to create a new image of Angkor as a place

that was teeming with life and full of activity.

LIDAR confirms that the city

spanned an area larger than the whole of New York City.

In the 12th century, when Angkor Wat was being built,

London had a population of 18,000.

It's been estimated that Angkor had a population

approaching three-quarters of a million.

Until the 19th century,

Angkor was the most extensive city in the world.

Bringing the old capital back to life

was only one of the project's ambitions.

LIDAR has also started giving revolutionary insights

into the origins of the Khmer Empire.

Since 1999, French archaeologist Jean-Baptiste Chevance

has been studying the Kulen Hills, 40km north of Angkor.

He has dedicated his life to uncovering

the remains of a 9th-century Khmer settlement.

It's a tough, simple existence.

I've been driving around for years, so I know the place pretty well.

I feel comfortable with the local people,

with the research, with the temples.

It's part of my life.

The dirt bike is fun, it's the easiest way to go from A to B,

especially in rainy season. Roads are turning into rivers, so you have to be cautious.

Historians believe that the Khmer Empire

began here in the Kulen Hills

300 years before Angkor Wat was built.

Before the LIDAR project,

Jean-Baptiste used conventional archaeology

to piece together a picture of an early Khmer capital.

This is Rong Chen temple.

Rong Chen sits on one of the highest peaks in the Kulen Hills.

At the time it was being built,

Anglo-Saxon Britain was being attacked by the Vikings.

Rong Chen is the only mountain temple in Phnom Kulen.

A temple made of different levels, like a pyramid,

it has always been considered the centre of the religious city.

Nobody has really studied and maintained this temple,

because Angkor was attracting most of the attention.

Inscriptions in temples built 200 years later

suggest that Rong Chen was the religious heart

of a new capital called Mahendrapravata.

And it was built for a powerful Khmer king, Jayavarman II.

Before his rule, Cambodia was a collection of small kingdoms ruled by local lords.

11th-century inscriptions suggest that Jayavarman

came to dominate the area by declaring himself

to be a special mediator between God and man.

Jayavarman II was the first king to unify those kingdoms.

He also installed a new cult of the god-king,

which made him even more powerful.

That cult was perpetrated by all the kings that were following him

and therefore Jayavarman II

has always been referred as the king who was unifying the Khmer kingdom

and starting the Angkorian period leading to Angkor Wat.

With only a few ruins and inscriptions to go on,

understanding the early days of the Khmer Empire has always been difficult,

and for many years, archaeological digs here were also impossible.

From 1975 to 1979, the Communist Party of Cambodia, the Khmer Rouge,

established a totalitarian state based on the teachings of Mao Tse Tung.

Under the leadership of dictator Pol Pot,

they ruled by terror,

rejecting urban culture and trying to build a self-sufficient agricultural society.

By the end of Pol Pot's rule

more than a million-and-a-half Cambodians had been killed.

Many more were left with permanent injuries.

The Kulen Hills was one of the last strongholds of the Khmer Rouge.

Until '96, it was completely impossible to come here.

At that time, the Khmer Rouge were occupying an artillery battery just behind this temple.

As a Westerner, you would've been kidnapped or killed.

Even the Cambodians couldn't come here, it would have been just too dangerous.

Today, the Kulen Hills remain heavily mined.

So this part of the Khmer Empire is one of the least explored.

Jean-Baptiste's work and his participation in the LIDAR project is changing that.

Laser information reflected from the surface of the Kulen Hills

revealed the shadow of Jayavarman's city

for the first time in more than 1,000 years.

The LIDAR results showed that Mahendrapravata

was a much more sophisticated city than anyone had expected.

It also covered a much greater area.

We found the urban network, which is massive,

which is covering at least 8km by 4km,

what you have here is the area which was covered by the LIDAR.

It's very, very surprising, because we passed over those sites for years.

This is a modern road we use almost every day,

but you go in the field and you barely see things.

We knew that in Kulen Hills you had a high concentration of temples,

one of them being the mountain temple,

but we didn't really know how it was connected together.

We didn't have the link between all these religious sites.

The LIDAR give us a complete vision, but in a way that is so spectacular

that we couldn't really believe it.

When we saw the result, that was like a big surprise, to be honest.

The LIDAR survey provides precise information

about where to look for the remains of further hidden structures.

This is a GPS, which allows me to know exactly where I am.

And we have downloaded the LIDAR result on it,

so I know exactly where I am, according to the LIDAR.

And I can check every feature,

I can check everything going back on the field.

In an area cleared of mines,

Jean-Baptiste is following up LIDAR data

that suggests the presence of an unexpected structure.

This is what I was looking for.

We have, actually, here two termites.

One here and one over there.

They're all in a line and this is not natural.

Termites don't build their mounds in straight lines in nature,

yet here there are six of them.

The LIDAR map suggests that the termites built their nests

on the remains of an earth bank built in the 9th century

at the edge of a medieval Khmer road.

So we're standing exactly on the blue arrow here.

What we have beneath is the LIDAR images

and on the top, we have highlighted the main road.

So if you go this way, you will see that line that we have on the screen here,

and this is exactly the bank of that massive road.

The termites are unwitting markers of a vast boulevard...

..80m wide, 6km long.

The size of these roads are amazing.

You could have a plane landing here,

you could have dozens of elephant running,

and probably hundreds if not thousands of people.

It would have been a very impressive sight.

The LIDAR images of Mahendrapravata

reveal that Jayavarman II began the construction of a remarkable city.

The Khmer people managed to clear tens of kilometres of jungle

to begin the construction of their new capital.

The LIDAR survey reveals a huge centrally planned metropolis -

canals,

reservoirs,

dams

and a network of giant boulevards

covering an area of at least 30 square kilometres.

We're actually here on a dam,

which is a massive dyke blocking the valley,

one of the main valleys of the Kulen Hills,

and it's running over 300 metres

and blocking right behind me a huge reservoir.

It's covered now by vegetation, it's a big swamp,

but at that time you have to imagine water all over.

LIDAR allows us to re-imagine this early Khmer city.

A huge reservoir of eight square kilometres

to sustain a rapidly growing population.

In a sense you could say that LIDAR is literally and figuratively

shining a light into these forgotten aspects of Khmer history.

The focus has always been on the temples and the monuments

and these elite aspects of Khmer civilisation.

For the first time we can consider the bigger picture

and put people back and consider these cities in all of their complexity.

Constructions like the dam

show that the city was ruled by a leader

who could plan and deliver huge engineering projects.

BIRDSONG

You have a massive structure

irrigating and controlling the water system up here.

This required a huge amount of labour,

therefore whoever is behind this is quite strong in terms of power,

in terms of politics.

A powerful political system was also needed to help overcome

one of the Khmer people's major challenges.

THUNDER RUMBLES

A metre-and-a-half of rain falls in the monsoon

between May and November, nearly 90% of the annual total,

and then, after six months of deluge, the long dry season begins.

Temperatures hover around 40 Celsius and for six months nothing grows.

If the crops fail during the wet season...famine follows.

The Khmer were obsessed with water

and at this river in the Kulen Hills,

they sought to sanctify it

by creating an elaborate underwater shrine.

These carvings in the rock of the river bed

were made in the 11th century,

200 years after Jayavarman founded his capital.

The shapes represent Hindu symbols of male and female fertility.

This is one of my favourite places here because it's beautiful.

It's a river bed which is completely carved for more than 1km,

carved with this symbol of the Khmer and the Indian mythologies.

This is a very unique place.

These intricate designs were carved to preserve life.

The water running here goes to the Angkor region.

This sacred carving brings a kind of spiritual value to the water

going down to the reservoir and to the rice crops.

The whole idea is quite magical.

Rainwater from the Kulen Hills flows over these carvings

down to the Cambodian plains.

The sanctified water sustained the staple of life for an entire people.

90 years after Jayavarman made Mahendrapravata a capital of his kingdom,

the administration moved here to Angkor.

Landscape archaeologist Scott Hawken

has been studying how rice farming shaped the new capital.

Mostly for the history of research on Angkor,

people have been studying temples, and the magnificent structures

that everybody talks about and notices,

but you can't understand the city until you go to the rice fields.

It's really interesting to start off

with the smallest elements of the archaeological landscape,

the humble rice fields,

and then to build up a picture of this mighty, mighty city

that was over 1,000 square kilometres in size.

The rice harvest here has always depended on a secure water supply.

I use satellite imagery, aerial photography

and map the rice fields

and the particular patterns that they make within the landscape,

then I can understand from these patterns

how the city developed over time.

THEY SPEAKS VIETNAMESE

He's been farming these rice fields here for many years,

and all this water comes from a local reservoir just upstream

which is 1,000 years old. So it's remarkable.

These rice fields have been watered by a reservoir

that his ancestor built 1,000 years ago.

Scott's work shows that the solutions found by Angkorian engineers

are still used today.

A successful harvest still depends on careful management of the monsoon waters.

Rice is a very demanding crop,

you really have to control water in a very precise way,

and this takes a lot of labour and energy,

and if you don't do this then the rice crops will fail.

At first, the people of Angkor tried to reduce the chance of failure

by building their city close to an enormous natural body of water.

Every year, these fields are nourished by the rising waters

of the largest lake in Southeast Asia.

Tonle Sap...the "Great Lake".

Tonle Sap is still critical to the survival of nearly a quarter of all Cambodians today.

It's only when you get down and are on the lake itself

that you really understand how vast it is.

It's just enormous. It's like an inland sea.

Even in the dry season, the lake covers

nearly 2% of the surface area of Cambodia.

During the monsoon it expands to cover

almost 10% of the whole country.

The edge of the Tonle Sap is a tremendously fertile resource

for around a million people.

As the lake swells and then as it shrinks,

it leaves this rich layer of silt.

But the people here had little control over the dramatic extremes

that Tonle Sap imposed on their lives.

During every monsoon the water rises by ten metres.

People living here today

are still forced to adapt to the lake's natural cycle.

So this fascinating village here, Kompong Phluk,

is perched up in the air on these enormous stilts,

ten metres high in the sky.

And this tells us something very interesting about the local environment.

In the wet season the waters here rise up,

so this village in the air becomes a village in amongst the water.

It's a remarkable village, it's really surreal, it's extraordinary.

People in the Angkorian era faced the same challenges.

There are two ways that a society can face

these dramatic climatic conditions of rising and falling water levels.

It can adapt like this village has

or it can actually take control and go beyond living on the margins

and really try to change the ecosystems and the environment

to suit the society itself.

The people of medieval Angkor chose to take on the environment

and to move from managed subsistence to a mastery of the landscape.

If you're a subsistence farmer it's a very precarious existence,

so the key really to surviving in this kind of landscape

is to develop technologies to overcome that inherent limitation.

The people of Angkor developed new engineering skills.

And nearly 1,000 years ago,

they built two huge reservoirs known as "barays".

Right now, just below us is the West Baray, the largest of the reservoirs of the Angkor period.

It's an absolutely huge construction,

it's 8km long on its north and south sides,

and 2km long on its east and west sides.

It's an incredibly impressive piece of engineering.

The West Baray is the largest hand-dug reservoir on the planet.

It can hold over 48 million cubic metres of water.

It's estimated that 200,000 people

were needed to construct its high embankments.

It's really remarkable to stand on the edge of the West Baray.

It's just an enormous, beautiful lake

built to precision engineering standards.

But it's not just a functional piece of infrastructure,

it's also really humbling and moving how beautiful it is.

900 years after the baray was completed,

its waters are still used to irrigate the surrounding fields during the dry season.

The West Baray is really the pinnacle of the Khmers' ability to transform their environments

and attempt to neutralise the flux of the monsoon.

If you look at society today, we're all about risk management, climate change.

They were doing the same thing back then,

trying to manage these droughts and to even out the disturbances,

so that the local population wouldn't revolt

and the kings could manage their society.

LIDAR work across Angkor shows how the Khmer people

transformed this area with advanced hydraulic engineering.

The elaborate network of canals and reservoirs

meant that they could now grow crops far away from the area irrigated naturally by Tonle Sap.

From an engineering point of view, what was achieved here is absolutely incredible.

They moved phenomenal amounts of the landscape from different parts of Angkor to other areas

and, basically, terraformed the entire plane into a completely artificial landscape

in order to release themselves from these limitations

of relying on the rainfall for one crop of rice per year.

A Chinese diplomat writing in the 13th century

marvelled at the Khmers' ability to harvest three or even four crops a year from their irrigated lands.

Once you've solved the problem of water supply, you've solved the problem of food security.

What you've done then is provided an extremely solid economic foundation for the growth of the empire.

The king can turn his attention to things like empire-building,

to warfare, to temple-building and so on,

and so it's a complete transformation, actually, in the way that things are done in Cambodia.

This mastery of the natural environment is one of the reasons

for the rise and the success of the Khmer Empire.

These engineering projects

demanded huge investments of labour and expertise.

The whole society had to contribute time and resources

to build the system of canals and reservoirs.

10km from Angkor Wat is Preah Ko temple.

Inscriptions on the walls of this 9th-century shrine

tell how the Angkorian kings

used the temple system to tax the population.

Archaeologist Julia Esteve has spent the last ten years translating them.

Most people think that temples are only religious entities,

but you have to understand the king, Jayavarman II,

the founder of the Khmer Empire

was at the same time a god

and used the temples to strengthen his economic and political power,

and so these temples are not only religious entities,

but also economical and political tools.

Temples had administrative as well as religious functions.

No coins have been found from this period,

it's thought the economy was run by exchange and barter,

with a duty to make donations to the temples.

There were contributions coming from the lower strata of the society made by rice farmers.

They would donate some of their time to the temple

in order to give some rice to the god.

With these kind of donations, we see another side of the temples,

and through the temples, the king would develop a system of taxation.

Inscriptions from the temple walls

suggest that payments took a surprising variety of forms.

This is one of the inscriptions.

And it's a fascinating text because it gives us the list of goods

donated to this particular shrine.

We have, for example, an umbrella-holder, a spice-grinder.

Also a garland-maker.

And along with this, we also have workers that would give labour.

But Julia's work has revealed

that people would also give up their own children.

We can see children. There is here a baby.

And over here there is a child who is at the age of running.

So children were donated to a temple or were considered as future workers

to help all the people who were here to serve the gods.

The inscriptions reveal a highly hierarchical society built on forced labour.

Julia's studies show how the Angkorian kings

built a network of religious shrines to consolidate their imperial power.

And LIDAR reveals the footprint of these religious buildings

across the medieval city.

LIDAR isn't just useful for areas that are covered by forest,

we also flew the instrument over large areas of open landscape.

And even in those areas, we're getting tremendous new insights into archaeological sites

that lie out in the open rice fields.

There are some things that just jump out of the imagery at you.

There are some classes of temples

that have a very, very distinctive layout.

5km from Angkor Wat, close to the edge of another huge reservoir,

the ghostly footprint of one of these buildings

appears on the LIDAR map.

300 metres in length and clearly broken into three sections,

these were "ashramas",

part monastery, part tax office, part school.

The building behind me is an ashrama,

and we know that there were communities of religious people living in the ashramas,

but we also think that some people, if they could afford it,

could send their kids to get educated,

maybe...to learn how to read.

These ashramas reveal the growing sophistication of Angkor.

Some were now wealthy enough

to invest their time in leisure and learning,

and their religious buildings were taking on a grander scale.

We're able now to say that they all had the same layout,

for those in Angkor at least.

And they were built around a central sacred building

where the religious people would gather.

Many ashramas were built on the edges of Angkorian territory,

a symbol of Khmer power

and a demonstration that the land around

belonged to a strong and unified empire.

We know from writings from the time

that the king needed money and a lot of people to build ashramas.

The building of more than 100 came at a period of great economic growth.

The king who built these ashramas all over the country

wanted to put his stamp on these lands

by saying, "This is my kingdom. I'm a strong king.

"I'm the best of the kings. I'm the king of the kings.

"And now these lands are mine."

By the end of the 11th century,

Khmer lands stretched across the modern-day borders of Vietnam,

Laos and Cambodia.

The Khmer Empire now dominated the region.

Mitch Hendrickson, an archaeologist from the University of Illinois,

has been studying how the Khmer expanded beyond today's borders of Cambodia.

We're actually following along the northwest road, which connects Angkor

to the site of Phimai, which is in modern-day Thailand.

The road extends roughly 280km,

so we're really following in the footsteps of people from 1,000 years ago.

The Khmer were the only people who built roads in Southeast Asia at this time.

By the 11th century, they'd built 1,000km of roads across the region,

a network that stretched to every part of their growing empire.

The ultimate result of this road network

is that it enabled the Khmer to become a regional superpower,

enabling them to branch off into different parts of Southeast Asia

and led to their ultimate control over mainland Southeast Asia for about 200 years.

Ox-drawn carts were used

to carry copper, iron and food to the capital.

As the empire expanded, trade improved the quality of life for the people of Angkor.

Today's travellers would have recognised some of the roadside developments.

40km from the capital - a medieval rest stop,

part temple, part restaurant, part refuge.

This is an excellent example of the type of infrastructure

and the desire to create support for travellers moving in and out of Angkor,

traders, pilgrims.

There would have been many people who would have stayed here,

seeking shelter from bandits

or just to get some water from one of the nearby ponds.

Along this road alone there are 17 rest areas

each spaced a day's walk - about 20km - apart.

Today, there's also an international frontier.

So here we are at the modern-day border between Cambodia and Thailand.

Of course, 1,000 years ago, during the peak of the Khmer Empire,

Angkor's influence actually extended into this region.

If I can find my passport...

Imperial expansion into new territories

also brought conflict and rebellion,

and Khmer kings were capable of mustering huge armies.

Carvings at Angkor Wat show a Khmer army on the march.

Thousands of soldiers able to travel fast to wherever trouble flared.

We're actually off to a temple now that commemorates the actions of one of the local lords

who helped put down a rebellion for one of the Khmer kings.

We're here at Phnom Rung...

one of the most impressive temples on the edge of the Khmer Empire.

Deep in enemy territory,

this temple was extended to mark a Khmer leader's victory over a local rebellion.

The large proportion of this temple that we see today

was actually an embellishment that was made in honour of that particular lord.

So we have this interwoven connection

between the civil conflict and external expansion,

which is interconnected with these road systems.

Beyond Phnom Rung temple

the road continues through what is now northeast Thailand.

The northwest road that we're tracking right now

is a little bit different from all the other of the Angkorian roadways

which brought what we think are more precious commodities such as metals.

The principal cargo passing along this road was a vital commodity.

The Khmer's great northwest road leads to a giant open mine.

It's still in use today.

This is one of the reasons why the Khmer travelled

hundreds of kilometres away from Angkor.

Salt.

What we're standing on now is a salt plain that we think was

probably used back to about 500 BC, during the Iron Age.

The salt would have been extremely important for so many reasons.

We know that without salt the human body can't survive,

and rice is one of the least saline of the cereal crops.

It was very significant from a physiological perspective

but, more significantly, we know that salt tastes good.

So from the peasants to the elite

and even the king, they would have desired this salt.

Then, as now, salt was an important preservative.

For a good chunk of the year you can get fresh fish, but in the rest

of the year you need to maintain your source of protein, and the way

that the Cambodians did it was

to create this lovely dish called prahok.

And prahok is essentially the salt from here,

taken down there to ferment this lovely and extremely appetising

fishy paste

that doesn't look good but I'm going to give it a little taste,

just to see how it goes, so let's try and find a bit.

Give it a whirl.

Whoof!

Ho!

Aw, man!

By the late 12th century, 300 years after

Jayavarman united the kingdom,

the Khmer had built the biggest empire ever seen in Southeast Asia,

and then a new king came to the throne, Suryavarman II.

His story is one of the best-known in Khmer history,

partly because of the reliefs carved into the walls of Angkor Wat.

Here we have Suryavarman II in all his glory,

probably the first time a Khmer king had been depicted in life.

He's surrounded here by his court.

We have the nobles, the Brahmin advisors,

and all around there's a scene which takes place in a forest.

There are animals cavorting around.

There are processions of people. Women carried in palanquins.

Soldiers... A scene of utter prosperity.

It looks fantastic, it's beautiful.

But this peaceful scene contrasts with the legend of how

Suryavarman II became king.

It's said that he stole the throne by raising an army against his

aged uncle, the Khmer king, and killing him with his own hands.

This section of Suryavarman's army has a quite a unique

body of men, and they're wearing very distinct uniforms.

An inscription actually identified them as being Siamese.

So this is one of the first depictions of the Thai people.

What it actually shows us is that Suryavarman was drawing

mercenaries from the extent of his empire to fight for him.

After the battle, Suryavarman brought his men back to

Angkor to work on the most important building project of his reign,

the biggest religious monument the world has ever seen.

It would draw on everything the Khmer people had

learned about architecture and temple-building.

Former UNESCO regional advisor Richard Engelhardt has spent

decades studying Angkor Wat.

Once he became the king, Suryavarman II imposed a great

peace over the entire empire,

so he built this temple as a way of saying, "This is

"the stability that I wish to impose upon our land,

"and this stability is going to continue and continue for ever."

It's the real pinnacle of the achievement of Khmer art.

Suryavarman wanted his Angkor Wat to eclipse everything that had

gone before.

We have to remember that this is a temple to the god,

and the god needs a universe populated with

beautiful things, with beautiful women, beautiful goddesses,

beautiful animals, and so they needed a

vast canvas on which to sculpt all of these magical creatures.

They did this by bringing these huge blocks of sandstone

here on site, fitting them together almost flawlessly.

There is no mortar, there's no mortar anywhere at Angkor.

They fit the blocks together very, very precisely.

Look, here's the sandstone blocks.

You can almost not see the join,

you certainly cannot even put your fingernail between it.

All the technical expertise and wealth of the empire was

channelled into this spectacular building.

Most striking of all was the scale of the construction.

Angkor Wat covers an area more than

four times larger than the Vatican City.

And this created huge challenges for Suryavarman's engineers.

During the monsoon, the land becomes saturated

and expands.

After the monsoon, it dries out and contracts.

How do you build high with such heavy material as this sandstone?

Well, look behind the facade and what do you see?

You see that it's filled with this very lightweight, porous

material called laterite.

It's a kind of ancient breeze block.

Laterite was a core building material of all Khmer temples,

stretching right back to the Kulen Hills.

Now it was used to help solve the Khmer's greatest engineering

challenge.

This building is much,

much lighter than you might think it is. The weight of the building

is not pushing, pushing down and pressing out on the earth,

but instead is rising up and you can build and build

and build almost as high as your imagination lets you build.

But Richard Engelhardt thinks that the use of laterite was only

part of the solution.

He believes that Angkor Wat is still standing today

because of the water surrounding the great temple.

In the ideal Khmer structure, you cannot separate

the building from the moat.

They are inextricable.

They are symbiotic and you cannot have one without the other,

both in the terms of the design and the conception

of what we are building and the civil engineering features of it.

Now, the Khmer were great artists, they never did anything that wasn't

beautiful, but the real purpose of the moat is not for decoration.

The construction of the moat surrounding Angkor Wat was

a huge operation. It's estimated labourers removed enough silt

and sand to fill St Paul's Cathedral ten times over.

Its perimeter stretches nearly 6 kilometres and is 200 metres wide.

Then the moat fills with water.

Water is heavier, it's more dense than laterite and earth,

so the weight of the water is actually heavier than

the weight of the materials you've taken out.

Richard believes the weight of the water in the moat pushes

back against the downward force of the stone temple.

The moat is essential to the success of the entire structure.

Without the moat, the structure could not stand.

The two are completely part of one holistic engineering system.

The Khmer had become masters of the monsoon.

Angkor Wat was an engineering masterpiece.

Everything the Khmer had learned over hundreds of years

of temple-building and engineering great water projects

came together in the construction of the jewel of their civilisation.

Through hundreds of years of experimentation

and gradual augmentation, we find that moving from a very,

very simple rice paddy to this extraordinary expression

of both civil engineering genius and an ability to communicate

through the symbolic meaning of Angkor,

this is what is so extraordinary about this particular monument.

Absolutely a stroke of genius.

The LIDAR project is enhancing our understanding of

the Angkorian empire and shedding new light on

the great civilisation that built it.

But it has also uncovered new mysteries.

Even though LIDAR has in, in some senses, transformed our vision

of Angkor by giving us new insights into the cities,

there are a couple of things which really took us completely by surprise.

Emerging from the LIDAR data by the side of Angkor Wat's moat,

the outline of eight huge coiled shapes,

partly obscured by the remains of a canal,

each one more than 700 metres in length.

Nothing like them has ever been seen before.

In terms of the features that we can see in the LIDAR,

those are definitely the most striking.

You wouldn't know it just to look down there,

you basically can't see anything from above except forest

right next to the moat of Angkor Wat right there.

These shapes have remained hidden for hundreds of years,

right next to one of the area's busiest roads.

We've launched a campaign of excavation

and closer study onto these features

to try and really come to terms with what they might be.

A team of Cambodian archaeologists is excavating

a section of one of these coils. They're looking for any physical

evidence - tools or pottery - that might suggest why they were built.

Some people have speculated that they're gardens,

that they're used for agriculture,

perhaps that they have some sort of ritual or symbolic dimension.

All the excavations so far have proved inconclusive.

No clues about their meaning or function have been found.

It's the nature of the game that there's not much

certainty here.

We might never understand fully what these things are.

And I guess, as archaeologists, sometimes we just have to

resign ourselves to that reality.

Angkor Wat marked the high point of the Khmer's artistic,

architectural and engineering skill.

It's a great symbol of a civilisation that grew from

the rice paddies of the Kulen Hills and came to dominate the region.

Angkor Wat is a peak of Khmer society.

It was a statement of where they'd come from

and where they were heading to.

LIDAR is revealing the epic scale

and sophistication of the Khmer capital

and helps to explain how the Khmer people

transformed their landscape and turned rice into gold.

Angkor is totally unique, and the things that were achieved here were

unparalleled throughout all of human history.

In the next programme, a vast new temple-building project,

the Khmer Empire's great metropolis faces destruction

and LIDAR helps explain why the Khmer people

allowed their capital to be devoured by the jungle.