BBC: Jungle Atlantis: Angkor Wat's Hidden Megacity

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.