All language subtitles for a.s.s02e02.1080p.hdtv.h264-cbfm_track3_[eng]

NARRATOR: In Asia, in Cambodia...

..hidden in the tropical jungle,

is the largest religious
structure ever built.

The majestic temple complex
of Angkor Wat.

A sprawling structure 1,500 metres
long and 1,300 metres wide,

covering 160 hectares,
larger than 200 football fields.

It's 200-metre-wide moat surrounds
an intricate central sanctuary.

Five gigantic towers, the tallest
of which soars 65 metres,

the height of a 25-storey building.

12th-century builders finished
this monumental temple

in just four decades, sparking the
fascination of archaeologists today.

Today, experts are using science
and technology to unlock the secrets

of Angkor Wat by revealing details
invisible to the naked eye.

This is a hand-held 3-D scanner.

What's incredible is that
we have a perfect virtual model

of the stratigraphy.

By scanning from the satellite
scale to the molecular scale

and the aerial scale, archaeologists
can now shed light

on the greatest enigmas of this
UNESCO World Heritage site.

How did the architects complete
this unprecedented project

in just a few decades?

How did the builders supply
this site with stone?

What secrets explain how

this thousand-year-old structure
remains standing?

The moat of the temple,
it's built in the concept.

The sand, when it's humid, it can
become strong like the stone.

Why was this monumental temple
built in the first place?

And what remains to be discovered

of the legendary city
that surrounds it?

We see this mound in many areas,

but we don't know
exactly what it is.

History, science, engineering
exposed as never before.

The Temple of Angkor Wat finally
reveals itself on every scale.

In south-east Asia is Cambodia.

In the north of the country
is an area known as Angkor.

It's a site known all over the world,

thanks to the unique remains
of the Khmer Empire.

More than 100 temples dating
from the 9th to 15th centuries

are hidden amongst 400 square
kilometres of tropical forest,

an area four times larger
than the city of Paris.

These legendary ruins are visited
by 2.5 million people every year

who all want to explore
one special temple - Angkor Wat.

It's the largest religious monument
on the planet,

dedicated to the god Vishnu
and built in just a few decades.

I think Angkor Wat
probably constructed

during the life of
King Suryavarman II

from approximately 1113 to 1150.

It's about 37 years.

So it's amazing, right?

An extraordinary feat because
every part of this superstructure

was built in stone,

a very heavy and labour-intensive
material to transport and use.

Examining the stones on
a microscopic scale reveals

that this is
a sedimentary rock - sandstone.

One cubic metre, it's about
one tonne, so it's very heavy.

The material choice raises a mystery.

Examining the site
on a satellite scale shows

that the nearest quarries are
many kilometres from Angkor.

Some of them came from
30, 40, 50 kilometres away

from the temples themselves.

The blocks of stone
are very, very heavy,

and literally millions of these
blocks had to be transported

from these distant quarries
to the sites of the temples.

We know roughly that
about 10 million blocks

have been used on Angkor Wat.

How did Khmer builders transport
millions of tonnes of sandstone

in such a short space of time?

To solve this mystery,

archaeologists today rely on
the most advanced technology

at their disposal to hunt
for clues on a satellite scale.

The Angkor Archaeological Park
is overseen

by the APSARA National Authority.

Kim Samnang is the director of its
geographical information system...

..a service that collects
and analyses mapping data

enriched in recent years by the
global view of satellite images.

The zone of Angkor is very big,
very huge.

And when we have these kind
of satellite areas,

we can learn more
how the ancient people

organise or set up their
urban cities in that time.

When we zoom in to the Angkor Wat,
you can see the structure,

the main temple here, the moat.

And then, another example,

you can see the Angkor Thom as well.

Examining the site on a satellite
scale exposes Angkor Wat's location

amongst a vast expanse of ruins.

To the north, the royal city of
Angkor Thom is surrounded by

a giant square moat.

A little further west,
the satellite images reveal

a huge rectangular area
eight kilometres long

and more than two kilometres wide.

We can see clearly from
the satellite, the 'baray'.

It's a reservoir that's
built by humans in that time,

built by hand, and can store
about 56 million cubic metres.

Satellite images also reveal traces
of other reservoirs now dried up

but all once connected to Angkor Wat
by a series of canals.

One of the more interesting features
that we see about Angkor

is its hydraulic network,

its network of canals
and reservoirs,

which has been the focus of a lot
of debate, a lot of research

and a lot of scholarship
in the last few decades.

There are many theories
about what these reservoirs

and canals represent.

A sophisticated irrigation system
for the population

or for sacred water to symbolically
bless the city?

But now another idea has been
suggested, and it could help

solve the mystery of how stone
was transported to Angkor Wat.

From the stone quarry site,
stone quarry site here,

there is one ancient road
that connects from here.

You see, the straight line
like this close to that area?

The latest scientific research
makes it possible to visualise

how the hydraulic network of Angkor
was once connected to the quarries.

At the foot of the sandstone source,
a network of canals and rivers

stretches some 40 kilometres all
the way to the centre of the city,

a route for efficiently transporting
millions of tonnes of sandstone.

By connecting the quarries
to the central area

of Angkor with canals,

and the blocks would be
presumably floated down the canals,

perhaps on rafts made of bamboo.

That was a giant undertaking.

Thanks to their ingenuity,

Khmer builders supplied their site
with vast quantities of sandstone.

Examining the material
on a microscopic scale

exposes that this sedimentary rock
is composed of 40% felspar

and almost 50% quartz.

These are very hard minerals,

which makes the stone
difficult to shape.

So how did workers building
these sandstone walls

carve the stones quickly?

World Monuments Fund is conducting
a restoration project

at Phnom Bakheng.

And this for us is a great
opportunity to get to see

more in detail about how
the temple was built.

Khmer engineers built the temple
of Phnom Bakheng from sandstone

in just 30 years.

Approximately in a day,

a team of two craftsmen
will cut and finish two blocks.

Here we're in front of thousands and
thousands and thousands of blocks,

so we can imagine how 30 years
was really actually a short time

to build this whole structure.

And what we also can imagine
is there were a lot of people

working in this working site.

To finish Angkor Wat
in just 37 years,

archaeologists calculate
that the labour force

could have numbered
in the hundreds of thousands.

But building the entire temple in
sandstone using traditional methods

would have taken too long,

so Khmer builders must have
discovered an engineering technique

that sped up the work.

In Phnom Bakheng, the dilapidated
state of the sandstone walls

gives archaeologists a surprising
clue about the construction process.

For instance, at this corner,

we can see that a lot of
the original wall stone units

were actually collapsed.

And this gives us a chance
to see more in detail

the foundations
inside the temple mounting.

In the case of Phnom Bakheng,

actually the temple mounting was
built around the natural hill.

Here, ancient builders laid sandstone

onto the bedrock of a natural hill
to save time.

But at Angkor Wat they
couldn't use the same trick.

It was constructed on
a flat foundation of sand.

Now 3-D modelling makes it possible

to visualise a remarkable secret
hidden inside the structure.

Underneath an outer layer
of sandstone blocks,

architects used a red rock
called laterite.

Actually behind
every sandstone unit,

which we see being part
of the raised platforms,

there are laterite blocks.

Examining laterite on a microscopic
scale exposes an iron-rich mineral

with a honeycomb structure

whose properties make it
particularly easy to work with.

When it is extracted,
when it is quarried,

it's actually very much
filled with water.

So it's just left drying
and then it hardens.

By building from the foundations up
using laterite

and then placing
the sandstone on top,

Khmer builders sped up
the construction of Angkor Wat.

But once the different types
of rock had been cut,

they still had to be lifted to build
the towers of the central sanctuary,

which are up to 65 metres high.

Today, restoration teams use cranes
to quickly move enormous blocks,

weighing between
one and three tonnes.

But in the Middle Ages,
without modern tools,

how did the Khmer builders
solve this problem?

With the help of
the latest technology,

experts can now reveal clues that
are invisible to the naked eye.

Today, a team from
the APSARA National Authority's

photogrammetry laboratory is
visiting the site of Banteay Thom,

a small temple built
a few decades after Angkor Wat.

Its towers are made of
thousands of sandstone blocks.

But how did builders reach the top?

The team plans to take thousands
of photographs to create a 3-D model

of the site and record
every tiny detail of the ruins.

The operation would be impossible
without the use of drone technology.

The drone is really important
for the 3-D model for the temple

because we cannot climb up
to the top of the temple.

So we need the picture on the top.

By flying over areas
usually impossible to reach,

the drone takes unique shots
of the temple,

covering a full 360-degree view
in minutes.

The team then processes
the photos on a computer.

They use powerful software
to automatically place the images

in a digital space and
create a point-cloud volume.

They can then texture the volume

to re-create the temple
in minute detail.

With this 3-D model, we can show
everything on the top,

on any direction from anywhere.

We can zoom inside and go
to see everything in accuracy

about the decoration,
about the structure.

And we can go any place
that we cannot go by the human.

By studying the 3-D model
of Banteay Thom from all angles,

the team finds strange markings
on the sandstone blocks.

Hundreds of holes from the base
to the top of the temple.

These are vital clues
to solve the mystery

of the construction process.

In Angkor Wat, we can observe in
many of these blocks, these holes.

And really refers to the way that
the stones were brought into place.

Originally, the holes
are where wooden pegs

would have been installed
in order to lift the blocks

and bring them to
their final location.

3-D imagery exposes a theory

about how Khmer engineers
used these holes.

They inserted large wooden sticks
directly into these notches

on each side of the stone, allowing
them to handle and move the blocks

much more efficiently.

But this doesn't explain how
builders lifted them so high up.

I think the way of moving the stone
from the bottom to the top,

using the scaffolding is not enough
to support the stone

because the stone is too large.

Simple wooden or bamboo scaffolding

could not support the weight
of the blocks.

So how did the builders haul
tonnes of stone

to heights of 65 metres?

Now archaeologists have found
new clues at the site of Rong Chen,

an unfinished mountain temple
dating from the 9th century,

allowing them to suggest a theory

that can be revealed
using 3-D modelling technology.

Builders constructed earthen ramps

to drag blocks to the top
of the construction site.

Then they dismantled
the temporary ramps.

Thanks to this ingenious process,
the Khmer builders were able to haul

millions of sandstone blocks
to the highest points of their site.

But once the blocks were in position,
the work was far from over.

The mystery is how,
in only four decades,

did the Khmer carve
kilometres of bas-reliefs,

thousands of small columns
and monumental towers.

To finish in time,
architects had to plan ahead

and ensure their work
was ultra-efficient.

The process of the construction
is the structure built first,

you know, from the base
up to the top,

and then the carving went down
from the top to the bottom.

It would have been extremely
difficult to carve the stone units

when they were not yet in place,

because only once the blocks are
perfectly sitting in their place

that it is possible to carve
the details to this level.

And it is thanks to this extreme
precision in the setting of stones

that we can now have the feeling

that basically
it's just one big stone.

Today, examining
Angkor Wat from the air,

the monumental temple appears
lost in the jungle.

And on the ground, the many
structures surrounding it

seem to have been abandoned.

But the temple walls are covered in
carvings that illustrate the lives

of people living in
a great civilisation.

So where did their homes go,

and how big was the city
that once stood here?

EVANS: The temples are made of
stone, they're very durable.

They survive relatively well
until the present day.

But the cities that grew up
around these monuments

were made of wood and other
non-durable materials

that have just disappeared
almost completely

in this tropical environment.

Which presents a real challenge
for us trying to reconstruct

what happened, you know, everyday
life around these temples.

Now scientists are lifting the veil

on the true size of
the city of Angkor,

thanks to a cutting-edge technology

that operates on an aerial scale -
LiDAR.

LiDAR can, like, take out
the forest from the ground.

Attached to a helicopter,
LiDAR uses light waves.

The rays pass through
the forest canopy

and are reflected back
to the LiDAR sensors,

allowing researchers
to chart the topography

of the ground in
unprecedented detail.

In 2012,
an international team scanned

an incredible 370 square kilometres
around Angkor in just 20 hours.

We were able to map huge areas
of the landscape very, very quickly

and with exceptional precision
and detail,

achieving in a few hours of flying
what may have otherwise taken

years or even decades on the ground.

Results were obviously
a revelation for us.

The LiDAR revealed something
astounding about the landscape

around Angkor Wat.

Hidden within the temple enclosure,

the team discover
an astonishing urban grid

made up of countless man-made
hills and depressions.

The Geographic Information
System Department keeps

all the LiDAR data collected
by the international teams.

See?

This is LiDAR areas.

Different colours represent
different elevations.

The darkest are the highest ones.

You can see the grid and
you can see the deep shape

upon the small points.

And the dyke.

You see? And a small mound.

And then the traces of the...
could be the road here.

That is the way the people
organise the cities.

This is the landscape
in which people lived,

for the most part,
in the central area.

In city blocks, square city blocks,

surrounded by roads or canals.

They built their wooden houses
on top of mounds

to stay above the floodwaters
during the wet season.

And they also dug ponds
into the ground

to keep water during the
dry season for household use.

Of course, the wooden neighbourhoods
have disappeared,

but the traces of their earthmoving,
the traces of these ponds and mounds

remain on the surface.

By using LiDAR, experts discovered
the hidden elaborate urban structure

filling the enclosure of Angkor Wat.

All around the sacred temple,

archaeologists have uncovered
more than 370 square kilometres

of urban structure.

Evidence of a high
population density.

It's very impressive, you know.

Through this information,
I can say there are many people

inside the compound, but also
outside the compound as well.

The picture that we have today
of monuments covered in jungle

are kind of cliched

and the temples themselves represent
in a way the kind of skeleton

of the society that lived there

in the middle of Angkor
a thousand years ago.

In fact, it would have been
a very busy place, full of life,

full of colour, full of noise,
full of people moving around.

These builders living at the foot
of the Angkor Wat construction site

form part of a gigantic
medieval city called Angkor,

the capital of the Khmer kingdom.

SOKRITHY: We probably believe that

more than 800,000 people
live in the capital city,

so roughly 1,000,000.

This is maybe the biggest city
in the world at 12th century.

At its height in the 12th century,

the capital was the centre
of a gigantic Khmer Empire

that can only be visualised
on a satellite scale.

From its very beginnings
in the 9th century,

the kingdom had an incredible
urban organisation.

EVANS: Angkor, in a way,
is unique in human history

for the degree of transformation
of the landscape

that took place as part of
this extraordinary project

of urbanism and engineering.

But how widespread were these
structures around the kingdom?

What was the real size of the city?

Now French archaeologist
Jean-Baptiste Chevance

is revealing the answer.

In 2017, his field work,
illuminated by a vast LiDAR campaign,

exposed the urban remains of one of
the very first cities in the empire,

located in a remote area 40
kilometres north-east of Angkor Wat,

the city of Mahendraparvata.

In this remote massif
of the Phnom Kulen Plateau,

teams used LiDAR
to sweep an enormous area

stretching 900 square kilometres,

revealing ruins previously
unknown to researchers.

Today, Jean-Baptiste is
trying to reach a temple

identified by this new technology.

He uses GPS to track his position
and plot a route.

It's the only way
to navigate the jungle

and reach the hidden ruins
in order to explore them further.

The temple is 40 kilometres
from Angkor Wat,

giving an indication of the scale
of the Khmer Empire ruins

hidden in the region.

But the most important discovery
revealed by LiDAR

remains invisible from the ground.

As early as the 9th century,

Khmer builders had constructed
residential quarters

around the temples,
stretching 1.5 kilometres

on each side, connected to each other
by large communication routes.

The discovery illustrates

the extraordinary building capacity
of the Khmer

from the very beginning
of their empire.

Examining the area
on a satellite scale

is the only way to expose the true
footprint of Angkor urban planning.

For more than 600 years,
builders constructed cities

and a vast communication network
throughout the empire.

There were very different scales
of infrastructural development

going on, from the local scale
where you had pathways and roadways

connecting houses
and neighbourhoods.

But it was also something much
bigger and much larger than that.

For instance, Angkor was connected
to various far-flung provinces

across mainland south-east Asia
by this vast network of highways.

If we, you know, calculate all the
road structures in the capital city,

it's more than 400 kilometres long.

But since the 12th century,

Angkor Wat has survived
the test of time.

So how did this UNESCO World
Heritage site remain standing

for nearly a millennium?

What are the secrets
of its incredible longevity?

According to Mr Im Sokrithy,

Director of the Conservation
of Angkor Park Monuments,

the 12th-century builders had learned
from their past mistakes.

They built a small pyramid,

but the temples collapsed.

3-D technology makes it possible
to visualise the structural problem

posed by heavy Khmer temples.

The monumental weight of
the sandstone towers

exerts phenomenal pressure
on the structure,

a pressure that tends to
push the stones to the sides.

The King of the Angkor Wat

understands that failure
of the structure,

and that's why they built
the central tower

with some kind of support.

The precision of 3-D scanned images
reveals a technique

that builders used which is difficult
to see with the naked eye.

Around the central tower, to counter
the forces exerted on the structure,

they placed 11 staircases intended
to act as buttresses.

But only the central staircase,
which was less steep,

could be used to reach
the top floor of Angkor Wat.

Many people misunderstanding.

This is the real staircase
getting up to the central tower.

But others were planned

used as supporting structure
to the central tower.

This secret of construction
allowed the towers

to stand the test of time.

Specialists have calculated
the number of stone blocks

and estimate that Angkor Wat
weighs 10 million tonnes.

A colossal mass built
not on bedrock

but on millions of cubic metres
of compacted sand.

A thousand years ago,
we don't have the technique

to make the foundation.

And the soil,
especially in Siem Reap,

is not strong enough

to support this kind
of heavy construction.

So what is the secret to
the sand's resistance?

Dr Hang is the director
of the APSARA National Authority.

A hydraulic engineer by training,

he has devoted his life to restoring
and studying the city's waterways.

According to his research,

the secret to the temple's
solidity is water.

The moat of the temple,
it's very important.

It's built in the concept.

By infiltration, they go to fit
the sand layer under the temple,

to keep the sand humid
to support our temple.

Once again, the latest technology
makes it possible to visualise

the ingenious concept
employed by the Khmer.

Thanks to the moat,
water seeps through the walls

that support the sand foundations.

But why is wet sand
any better than dry

at supporting 10 million tonnes
of temple?

We can say the sand when it's humid,
it can become strong like the stone.

The Khmer ancestors,
they understand that very well.

Examining the sand
on a microscopic scale

exposes what makes this material
particularly resistant.

Water distributes amongst the grains,

acting as a glue
between each particle

to create a new state,
a solidified sand aggregate.

The enormous moat of Angkor Wat

contributes to the incredible
longevity of the temple.

But the engineering challenge
can only be fully appreciated

on a satellite scale.

In order to sufficiently
moisten the foundations,

the moat is proportional to
the scale of the monument -

200 metres wide,
5 kilometres in circumference,

containing up to 1.5 million
cubic metres of water.

The moat is connected to
a network of canals and reservoirs

to guarantee the stability of the
temple, even in the dry season.

The temple,
it's built for the god.

So it is why they want to make sure
that the temple, it stands forever.

Restoration work allows experts
to decipher the ancient techniques.

Because the blocks need to
interlock with each other,

we need to make sure that
there is a perfect match

between a stone
and the one next to it.

When we look at the Angkor temples,
we're often fascinated by the fact

that the joints in between blocks
and between sandstone blocks

are extremely, extremely thin

and so tight that we cannot even
slip a credit card inside.

How did they make such
perfectly fitting joints

to lock the blocks together?

This was actually achieved,
this technique

of rubbing, or frottage,

where basically the two blocks
would be rubbed together

with each other,
against each other,

and an abrasive sand
would be placed in between.

And so they would have been rubbed
until the fine joints were reached.

3-D imaging technology exposes

the technique used
by the Khmer builders.

By means of abrasion,

the irregularities of the sandstone
are ground down

until the blocks fit
together perfectly.

Then when they erected the walls,

the builders would slide a smaller
stone called a key

between the large blocks,
which would lock the structure.

Sandstone and laterite were not
the only materials used

by Khmer craftsmen.

In 2012, an important discovery
brought to light

other ancient techniques.

The discovery sheds light
on a little known aspect

of Angkor craftsmanship.

They adorned temples and sculptures
with decorations of precious metal.

The central towers were
covered with gold leaf.

But the Khmer used metal
for more than just decoration.

Builders cut notches in the sandstone
to fit metal pieces,

many of which, like the decoration,
have been stolen by looters.

What did these objects look like

and what were their roles
in the temple's engineering?

This question is now being
closely studied by science.

In the CEA Paris-Saclay laboratory,

archaeometallurgist Stephanie Leroy
uses the latest technology

to decipher the history
of these mysterious objects.

Today she is studying
a precious specimen

dating back nearly 1,000 years and
found in 2018 on the Angkor site.

3-D imagery helps visualise
the role of these metal clamps

in the structure of the temples.

These objects were used to join
the sandstone blocks together.

Examining the metal
on a microscopic scale

exposes a material
that is easy to work with

to create the shape
of the clamp - iron.

This very resistant metal
was usually used by the Khmer

for weapons and tools,

but here it was used to reinforce
the structure of the temple.

In Angkor Wat, builders placed
hundreds of thousands of clamps

inside the structure to ensure
impressive longevity.

This latest revelation poses
a new mystery for archaeologists.

Where did the Khmer find so much
iron to build this temple?

By studying clamps from Angkor Wat
before they are restored,

Stephanie looks for clues
on a microscopic scale.

Thanks to cutting-edge technology,
a scanning electron microscope,

the laboratory is now trying
to determine

the origin of the Angkor Wat
clamps on a molecular scale.

On satellite images, the quarry site
is located in Phnom Dek,

literally meaning the Iron Mountain.

The site is some 100 kilometres
east of the city

and has been exploited
since the 11th century.

But when samples from the temple
of Angkor Wat itself were studied

in 2020, the results were unexpected.

The origin of the iron
used at Angkor Wat

remains a great enigma
of this sacred temple.

The Khmer built this engineering
wonder with one goal in mind -

to build an eternal monument.

But this building is still
shrouded in mystery.

Why did King Suryavarman II
order the construction

of the largest temple
ever to rise from the ground,

and what does the
fascinating architecture

of this incredible
monument symbolise?

In the 19th century,
when archaeologists began to study

the symbolism of
the largest Khmer temples,

it was impossible for them to easily
visualise its gigantic plan.

But today, thanks to the latest
satellite technology,

archaeologist Ginevra Boatto can
observe the entire 160 hectares

that the building covers.

The use of aerial pictures
or satellite images today

is very helpful in the sense
that it helps us

get a better understanding,
seeing better

these incredibly huge structures
like Angkor Wat.

It measures 1,500 metres

along its west-east axis

and 1,300 metres along
the north-south axis.

When we look at its moat,

a total perimeter of
5 kilometres, approximately.

But why build a moat and a monument
of such magnitude?

The architecture has been
designed for the heaven

and they apply it on the space.

When planning Angkor Wat,
the architects were inspired

by the image of
the heavenly paradise

according to Hindu mythology.

3-D modelling makes it possible

to better decipher the hidden
symbolism of Angkor Wat's layout.

This pyramidal structure
called Temple Mountain

is topped by five towers,

representing the five peaks of
a mythical mountain, Mount Meru,

home of the God Vishnu,
to whom the temple is dedicated.

A sanctuary surrounded by not one
but three stone enclosures

evokes the mountain ranges
surrounding the celestial residence.

Finally, the gigantic moat
symbolises the cosmic ocean

separating humans from the gods.

In a kind of a magical way,

a certain power is also
given to this place.

This temple becomes
a heavenly palace,

it becomes heaven on earth.

The king wanted a paradise on earth
but his ambition didn't stop there.

To understand, you have to look at
the structure of the temple

on an aerial scale.

In this case, specifically,

when we look at one
of these aerial views,

we can appreciate a geometric
pattern, which is called mandala...

..which was commonly used
in Hinduism and Buddhism,

which shows a square with the four
openings at the four cardinal axes

and the circle inscribing it
with a central point.

This central point represents
the axis mundi,

the central axis of the cosmos.

Therefore, having this kind
of geometric pattern

imposed on Angkor Wat means
that Angkor Wat is placed

around the axis of the world
and is the axis of the world.

Builders used this symbol
for the foundation of the temple.

Khmer engineers first drew
the sacred mandala

directly on the ground to define
the location of the superstructure.

Then they dug out the earth
to place the foundations

in the form of a huge amount
of compacted sand.

During the excavation of
the foundation for Angkor Wat,

a well was also dug at
the bottom of the foundation.

Today, 3-D modelling techniques help
to expose the mysterious structure

discovered in the 1930s.

From the foot of the central tower,

a 20-metre-long well
joins the base of the temple

where the builders dug a cavity.

But why did they form this structure
within the foundations?

To better understand the role
of this underground cavity,

experts travelled some 100 kilometres
north of Angkor

to the site of another Khmer temple.

This is Prasat Khnar,

a little-known site
whose construction began

approximately three centuries
before Angkor Wat.

Now, for the first time,
an international team

is carrying out
an excavation campaign

to understand its history
and construction.

One long building is of
particular interest to researchers.

It's an ashram, or monastery,
dating from the 9th century

and partially destroyed.

The floor has long disappeared,

giving archaeologists a unique
opportunity to dig a trench

and study the foundations
of the temple.

It's a chance to discover
what could be hidden

in the depths of Angkor Wat.

The study is facilitated
by cutting-edge technology

now being tested by these
University of Toronto researchers.

This is a hand-held 3-D scanner
that uses two cameras

and a light system
to develop an image.

It's called stereoscopic vision.

So, you have two eyes in order
to have a sense of depth.

This does exactly the same thing.

The scanner uses stereoscopic vision

similar to the principle
of human vision.

Both camera images are sent
directly to the internal computer.

Instantly, just like the brain,

a software program calculates
a three-dimensional model,

allowing archaeologists
to study bas-reliefs,

statues and other ruins
in precise detail.

But today, this tool is
an opportunity to observe

the foundations of
the Khmer monastery

and reveal details
in three dimensions.

You can really pick up the relief
there, you see, Giles?

And from that basis you can draw
the actual stratigraphy.

That's nice.

In just a few minutes,
the trench is fully modelled.

If I can take a look
at what you have here.

It's very good. OK.

So what's incredible is that
we have a perfect virtual model

of the stratigraphy.

So in a sense, if this was ever
destroyed or once it's buried,

we can revisit the trench
and reanalyse it.

By zooming in on this digital model,

the archaeologists observe a recess
which forms a small cavity.

So, in fact, we found
a small looter's pit

that didn't go very deep.

From this pit, looters stole
precious objects

that had been placed by the builders.

But which is very common in
Angkorian temple construction

is offerings that are placed right
at the bottom of the foundation

as a way to bless and sanctify

the major cult building of
the monastery that was founded here.

It's likely that many years ago,
this temple was, in fact, looted

for these very precious objects.

Situated 20 metres below
the main tower,

at the very heart of the foundations,

this space, sheltered from looters,

was used to protect
precious offerings to the gods.

But some archaeologists believe
this cavity had another function.

They think the Khmer deposited the
ashes of King Suryavarman II here,

meaning that Angkor Wat is more
than a temple, it's a gigantic tomb.

No coffin or ashes that could prove
this theory have been unearthed

during excavations, but the idea is
commonly accepted by archaeologists.

Angkor Wat, the largest
religious building on the planet,

was built at the request of the king
to embody the centre of the universe

at the home of the god Vishnu.

This symbol of Khmer civilisation
has survived for almost 1,000 years.

But according to the legend,
the capital of Angkor

brutally disappeared
in the 15th century.

So how did this enormous city,

finally revealed by LiDAR,
really decline?

Why did the population leave
this gigantic capital?

There was an idea, for instance,
one theory

that something catastrophic
happened at Angkor

and there was a mass migration
of people away from Angkor

into alternative places.

Many theories exist about
the disappearance of the capital...

..the occupation of forces from
the nearby Ayutthaya kingdom,

violent political
or religious disorders...

..or natural disasters that forced
hundreds of thousands of inhabitants

to leave the city in a hurry.

In fact, the LiDAR tends to show us
that that was not the case,

actually, because the cities
that came after Angkor

were very modest in size
by comparison.

What we really need to do
from that point onwards

is to complement these horizontal
surveys we've provided by LiDAR

with other kinds of information
right down to the microscopic scale.

In 2019, to check whether or not
the city had suddenly been abandoned

by its Khmer population,

an Australian team turned to
microscopic research.

By carrying out core sampling
and collecting soil samples

from the moats of Angkor Thom,

scientists studied sediments
present in the soil,

exposing a biological
archive of the city's history.

Pollen analysis made it possible
to determine the precise use of land

year after year.

EVANS: What we would
then expect to see

if there were periods of abandonment

is gradually species
reclaiming that landscape

and eventually pollen from forests
reappearing

at the top of that archive.

That was not the case, actually.

What the cores have shown
is that there was a very gradual

resumption of this sort of jungle
environment at Angkor,

spanning many, many centuries,

and probably a progressive
abandonment of particular areas,

even as other areas continued to
function and remained occupied.

But just as advanced technology
has shed new light

on the history of Angkor, it
has also raised new mysteries.

Following the LiDAR campaigns,
archaeologists discovered

strange alignments of earthen mounds
at various sites,

360 structures whose function
are still eluding specialists.

We see these mounds,
these alignments,

and mound, a small mound like this,

in many areas, like Phnom Kulen,
as well.

But we don't know
exactly what it is.

Decade after decade,
archaeological research,

aided by the latest technology,
has exposed many of Angkor's secrets.

From the gradual decline
of the city from the 15th century

to the mountain temple
symbolising paradise on earth,

built in just a few decades,
using ingenious techniques.

Scientific progress has
allowed investigators

to reveal an incredible capital

hidden underneath
vast expanses of forest.

But many great mysteries
of the Khmer builders

remain to be solved.

BOATTO: Basically, everywhere
there is a new temple, a new ruin

that has been discovered
in the jungle, among the trees.

So it's a never-ending experience.

And there is so much still left
to understand

and to discover
about this civilisation.

Captions by Red Bee Media
(c) SBS Australia 2022