All language subtitles for Ancient.Superstructures.S01E02.720p.HDTV.x264-CBFM

In Peru, in the heart
of the Andean mountains,

built at an altitude of 2430 metres

on a rocky ridge
surrounded by steep, rainswept cliffs

stands the city of Machu Picchu.

Machu Picchu is the most
impressive living testimony

of Inca civilization.

It's absolutely breathtaking.

Frequented by
over 800,000 visitors each year,

this Inca city, built
in the middle of the 15th century,

at the height of the Inca Empire,

remains, in the eyes of many,

this civilisation's most amazing
and enigmatic urban creation.

From an engineering point of view,

we just have to stand back and say,
"That's really impressive."

As an architect, I really wish
that I could have a time machine

and go back in time
and see how they did it.

Today, with the help
of new technology,

experts can turn back the clock,
by probing the invisible

and exploring what is hidden
beneath and around the city,

to expose its secrets.

To understand
the magnitude of Machu Picchu,

we'll have to see it
from very high above.

What we don't see
is that 60% is underground.

How did extraordinary
Inca civil engineering

overcome
the most violent natural threats,

and transform this extreme terrain
into the empire's most famous city?

What are the construction secrets
behind these unshakeable buildings?

What do these iconic terraces hide?

What amazing astronomical engineering
are these massive stones concealing?

And what is left to be discovered
about Machu Picchu

in its most impenetrable areas?

Machete!

Thanks to advances in technology,

Machu Picchu is revealing itself
to today's experts

in extraordinary new ways.

Surveying the depth of the mountain,

scanning from above
and exploring the ruins,

they will
share their most recent discoveries,

and allow us to enter areas of the
site never before seen by the public.

It's unique,
and it's the only one of its kind

still standing up
in the whole Inca Empire.

Exploration, science, construction.

Examined close up
and from space alike,

Machu Picchu strips down
and reveals itself on every scale.

Declared a UNESCO World Heritage
site in 1983,

the incredible sanctuary of
Machu Picchu covers 32,592 hectares

of mountainous slopes,
peaks and valleys

embedded in the heart
of Peru's tropical rainforest.

But it's just one small part
of this immense site

that is well known to the world,

the breathtaking city,
of almost 200 buildings,

built in 1450
at the height of the Inca Empire.

The nuclear part of Machu Picchu
is what we see,

but within 5 kilometres
there are other sites that probably,

in the master plan of the Incas,

were going to be integrated
into Machu Picchu.

Today, most people only know about

a tiny fraction
of the entire Machu Picchu site.

For more than a century, since
the rediscovery of the city in 1911,

explorers and scientists
focussed their research

on the heart of the citadel,
the area's most recognisable part.

But now, investigators have the means
to carry out their studies

and focus their research on areas,
which have remained invisible

to the eyes of its visitors
until today.

The goal of this exploration work

is to solve a series of intriguing
mysteries, the first one being,

what secrets are hidden in the
remote terrain surrounding the city?

What is the true extent
of this extraordinary sanctuary?

In order to understand
the magnitude of Machu Picchu,

its position and its relationship

with all the other sites,

we will have to see it
from very high above.

To comprehend the extent
of this famous Inca sanctuary,

and better understand
the archaeologists' ground work

First, it is necessary
to get a bird's-eye view,

and use satellite imagery
to visualise Machu Picchu's position

on different scales.

From above, we discover Machu Picchu

at the summit of a mountain
with the same name,

then the mountain,
at the heart of the Peruvian Andes,

and finally, its location
within the Inca Empire

and the empire's
gigantic network of ancient roads,

which traversed no fewer
than six modern-day countries,

from the south of Colombia,
to the tip of Chile and Argentina,

weaving through
the most important Inca sites.

Experts believe

that the number of roads linking
a city to this immense network

could reveal the site's importance.

This is why a large part of recent
excavation work at Machu Picchu

has been devoted to the exploration
of new segments of road,

which would link the city to the rest
of the sanctuary and to the empire.

It was once thought
that Machu Picchu was isolated,

but then the road network
was discovered.

On a yearly basis, we find
new roads or new segments of roads

during our explorations
within the sanctuary borders.

And it is absolutely incredible.

It is a network that spans
the entirety of the empire.

To find and clear these new trails
in the heart of the rainforest

the site's official archaeologists
first rely on traditional methods.

They start by collecting information

about the potential presence
of sections of road,

by studying historical documents

and interviewing the local population
who know the terrain well.

Once this information
has been collected,

and areas of special interest
identified,

they swap traditional groundwork
for new technology,

which operates at an aerial scale.

This is LIDAR, a technology
which uses airborne lasers.

LIDAR allows for reconnaissance
work before exploring the ground.

Fixed to a plane,
helicopter or drone,

the device scans
an area defined by experts.

It emits light beams
that it sends towards the ground.

These beams pass through
tiny gaps in the vegetation.

When they reach the ground, they are
reflected back to the transmitter,

recording the terrain's contours.

LIDAR makes it possible to confirm
the presence, and precise location,

of sections of road.

Nowadays, after
the latest 2014 discoveries,

we have nine roads
that arrive to Machu Picchu.

They are all connecting Machu Picchu

with all the other
settlements in the area,

and, within the sanctuary borders,
we have more than 300 km of roads

that interconnect everything
as a spider web.

And the roads
weren't just for everyday use.

You had to have
special permission to be on them.

Not everybody
was allowed to enter Machu Picchu.

The discovery
and clearing of trails,

has revealed the presence
of numerous control posts

built to filter access to the city.

Ingenious checkpoints,
located at regular intervals,

such as these suspension bridges,

from which the Incas could remove
wooden logs to deny visitor access.

Or entrance ways
once fitted with doors

to control access
to various sacred sites of the city.

Here, we are very close
to the sun gate, Inti Punku,

but before we get there
we have this double jump door.

This is what we call
a double jump door.

It's two levels of the door

and probably
this would have had two lintels.

Having a double jump door

means that you are entering into
a more important or sacred space.

Safe passage
was an important part

of the society
surviving in that landscape.

The network of roads the Incas
created across very hostile terrain,

was an information highway
akin to the internet of our own age.

They were mainly for military use

and of course you had runners who
would take messages back and forth,

and they travelled
hundreds of kilometres a day.

It's quite amazing.

Exploring this network
of highly-protected roads,

is allowing the site's archaeologists

to understand the true significance
of this now famous citadel.

A city, which is beginning to look
more and more like a megalopolis,

as additional sites
within the sanctuary are discovered.

There are still a lot of things

that we are starting to understand
about Machu Picchu.

So, in the last five years,

we have been intensively excavating
not only Machu Picchu,

but other sites within
the historic sanctuary borders.

By exploring this network of sites,

investigators have unveiled
a new gateway to the citadel,

a site called Chachabamba.

The ruins of this site
were first discovered in 1940,

but now investigators
are undertaking a new campaign

of archaeological excavations.

A satellite scale makes it possible

to visualise
the exact location of Chachabamba,

a gateway to Machu Picchu
positioned in a valley

7 kilometres
from the heart of the city.

The site exposes the vast size
of this historical park.

But it is excavations on the ground
that allow archaeologists

to determine what links this site
to the city.

They have discovered a remarkable
concentration of 14 fountains,

which shed new light

on the importance of Machu Picchu
within the empire.

Dominika Sieczkowska
is an archaeologist

from the Centre of Andean Studies
at the University of Warsaw in Cuzco.

Today, she is leading a team
to explore a new area of Chachabamba.

She is hunting for other structures
which could, like the fountains,

offer precious information
to experts.

Several days ago,
the archaeologist and her team

scanned the area using LIDAR.

Now, she is back in the field
to uncover mysterious structures

that the device has located
in the jungle.

Structures not possible to locate
so quickly with the naked eye.

For aerial LIDAR technology to be
useful to Dominika and her team,

she works with researchers
who first analyse the data,

then send her
the precise geographic coordinates

of any structures
which have been located.

In addition to these geographic
coordinates, Dominika has received

an infrared image of the structure
scanned by the LIDAR.

The image provides clues

about the shape of the structure
she is trying to locate.

The wall Dominika has located today
will soon be excavated

and can then be 3D modelled
and studied in closer detail.

This scanning and exploration work,
which was started several years ago,

allows researchers
to improve and clarify

the mapping
of the Machu Picchu sanctuary.

But it also allows them
to model the explored areas.

Sites like the citadel itself

or the additional sites,
like Chachabamba.

This is an invaluable
technological advancement

for the understanding of this area.

Today, experts have access
to perspectives and scales of study,

which would otherwise remain entirely
inaccessible to the naked eye.

As well as
contributing to revelations

about Machu Picchu's true scale,

this new method of exploration

is beginning to reveal
answers to another key mystery.

What was the function of Machu Picchu
within the Inca Empire?

In Machu Picchu, they've put
a community on top of a mountain,

and that suggests that they wanted

something other than
just to build a city or a community.

It has something else
which was important to the Incas.

Thanks to the research that we have
been doing in the past few years,

now we understand a little bit more
the function of the different areas.

And we can say that Machu Picchu
is a multi-function site.

The exact nature
and number of functions

that Machu Picchu
had within the empire

is still cause for debate
amongst experts.

But a recent discovery has finally
allowed for agreement on one.

Machu Picchu's role...

as an astronomical observatory.

The most impressive part
of Machu Picchu

are basically
the astronomical observatories.

It was very important for the Incas

to observe closely
these astronomical phenomena.

It's not only because
of the ritual calendar of the Incas,

but also it was related to the
moment of planting and harvesting.

Like many farming civilisations,

the Inca organised their lives
to the rhythm of the seasons.

Observing the sky
and the movement of the sun

was essential to keeping track
of the passing seasons,

and in anticipating the arrival

of particularly violent rains
in the region.

Experts have long known
about a few key sites in the city

that were designed
for astronomical observation.

But, two years ago, for the first
time in Machu Picchu's history,

investigators used new technology
to uncover a remarkable site,

unlike any other found in the empire.

Machete!

A unique observatory hidden
under the tropical jungle vegetation,

on the north face
of the Huayna Picchu mountain,

which has never been
revealed to the general public.

This place
is El Mirador of Inkaraqay.

And it's basically
the only Inca structure of its kind

that is still standing.

This unique site, which
can now be located by using LIDAR

to virtually
clear the area of its vegetation,

was spotted for the first time
in 1980,

by the archaeologist,
Fernando Astete.

But due to a lack of means, it
wasn't until 30 years later, in 2012,

that an excavation campaign
was started on the site.

Overlooking a foundation terrace,

archaeologists discovered
the remains of walls,

with stones that had been cut
particularly carefully and regularly.

Preparation of the kind

reserved for buildings of prestige
and of high importance to the Inca.

On the main facade,

the archaeologists
also located two openings,

very different to anything
they had discovered

on other walls built by the Inca.

So, in this fine masonry wall,
what we have is two orifices.

One here, and one over there.

Convinced they had uncovered

a structure built
for a very particular function,

they decided
to return the next year

to run a more advanced investigation

that would finally
unravel the mystery of this building.

To see further than the human eye,

the archaeologists teamed up
with Polish researchers,

to organise the scanning
of the entire site.

Their aim was to model it
and expose its function.

Without scanning or modelling,

there would be no way
for experts in the field

to study the structure
in its entirety.

Its location, on the steep slope
of a mountain side,

makes it impossible to observe
the building's layout and parts

as a whole.

So, it was only
thanks to a study of a virtual model

that investigators could reveal
the secret of its true function.

With the recent investigations
made by Fernando Astete

and Professors Ziolkowski
and Kosciuk,

now we know for sure

that this is an astronomical,
a precise astronomical instrument.

The unique perspectives
given by the 3D model

allowed
Polish and Peruvian scientists

to carry out a detailed study of the
two openings that had intrigued them.

They first discovered that the
orientation of these two openings

made it possible for the Inca

to form a horizon marker from
the sacred summit of Mount Yanantin,

situated
to the north of Machu Picchu.

Then, they reconstructed the ancient
positions of celestial bodies

to establish what exactly
the Inca astronomers were observing

through the holes.

Today 3D modelling
offers us a unique opportunity

to recreate the past and discover
what the Inca saw 500 years ago

when they looked through
the openings of this building,

which is now known
as the Inkaraqay observatory.

What we have here is an instrument

that the Incas will use
to watch the June solstice

and also the Pleiades.

The orientation
of the southern opening

allowed for the perfect
study of the rising of the Pleiades,

a group of stars whose brightness,

and position
in relation to Mount Yanantin,

allowed the Inca
to forecast the seasons.

The northern opening allowed them
to detect, with incredible precision,

the day of the June solstice.

Inca astronomers
managed to orientate this opening

so that it let in the sun's light

precisely when
it rose over Mount Yanantin,

but only upon
the exact day of the June solstice.

As well as determining

the extraordinary function
of this structure,

scientists have solved
the mystery of how it was used.

So, we are in the inner part
of the El Mirador structure,

and what we have here
is the two orifices.

How these things function...

The priest astronomers will,
in this case in the left orifice,

they will not look directly,
because...

looking directly into the sun
can get you blind.

They will just
see the projection of the light

here on this other back wall.

And for watching the Pleiades,

the priest astronomer will position
himself here inside the niche

and will watch through the orifice.

It's absolutely breathtaking.

They wanted isolation and they
wanted to be closer to their god.

Here in Machu Picchu,

they have an incredible
understanding of their environment.

Technological progress

and the tireless work
of experts at Machu Picchu

is revealing the genius of the Inca,

and exposing their extraordinary
knowledge of the environment.

Some of the most glaring proof
of this knowledge

is revealed in the construction
of the city itself,

built on a particularly hostile site
with difficult access

and extremely high rainfall.

Tons and tons of rain falling
from the sky every single year.

So you need to slowly release it.

And if you don't deal with it
in the right way,

it's just going to wash
your civilization down the hillside.

Both a deadly threat,
and an essential element to man,

the problem of water has long been
at the heart of explorers' research.

And it still interests experts today.

How did the builders of Machu Picchu

manage to both protect the city
from this devastating element

and exploit it to survive?

How did Inca engineers manage to rise
up and solve the challenge of water?

Rainfall, at the time,
when it was built,

is estimated to have
been around 2 metres a year.

Even today, floods and landslides

regularly destroy
homes and roads in this region.

But Machu Picchu's buildings have
survived for over five centuries.

We could learn a thing or two
from the Incas.

You know, the way
that we design our cities today,

we need to think about
how we deal with excess water,

how we deal with run-off.

No written testimony by the Inca
has ever been found.

So, it's only by searching for clues
in the exposed parts of the city

that experts have managed,
piece by piece, to unravel the secret

of how the city withstood the
devastating threat posed by water.

More than 50% of the effort

dedicated to build Machu Picchu,
it's underground.

If we look at Machu Picchu,
we see buildings on the surface,

what we don't see
is that 60% is underground.

60% of that city is dealing
with water and getting rid of it.

The secret to the city's survival

was found hidden underground,
beneath the feet of its visitors.

An ingenious
underground drainage system,

the visible parts of which
are these iconic terraces.

Surprisingly, the best way to measure

the extent
of this underground system,

is to take to the sky,
and scan the site on an aerial scale.

From the air, we discover the
incredible scope of these structures.

a succession of staircase terraces
of exceptional regularity.

They act as an armour
around the citadel,

covering the steep mountain slopes.

But it's by probing the depths

that we discover the true genius
of these structures

A natural drainage system,
invisible to the naked eye,

which allows the control of rainwater

and the protection
of the mountain from landslides.

So, this is an example
of a retention wall of a terrace.

Now, inside these terraces,

what we have will allow rainwater
to infiltrate slowly,

and it won't affect the structure.

It was excavation work
that allowed past experts

to understand
the function of these terraces

and their stages of construction.

Stages which 3D imagery
can now recreate.

To construct these terraces,

Inca builders started
by erecting a retaining wall

on the steep side of the mountain.

Then, they filled in
the area behind this wall,

with four layers
of different materials.

What we have is big rocks,
then medium gravel,

then we have
some sand mixed with fine gravel

and then we have the fertile soil.

And then this just gets rid of the
water in a controlled environment.

The layers
of different-sized material

stop the ground
from getting overly waterlogged,

which would weaken it.

It also regulates
the release of water.

The Inca constructed these terraces
one by one,

shaping this incredible
staircase structure

cut into the mountainside.

It's the foundations

for an effective
drainage of rainwater

that have made Machu Picchu
survive for hundreds of years.

If they didn't do that, if the Incas
hadn't put these systems in place,

they wouldn't have
had a citadel to talk about.

It would have been washed
down the hill, it would have gone.

That is
one of their engineering skills

is to realise
where the threat comes from

and then to address that threat
through design and engineering.

In the last 20 years,
with the systematic excavations,

we understand way more
about how Machu Picchu was built.

Excavations
and traditional research

allowed experts to determine
the function of these terraces.

But today, investigators
are using new technology

to gather fresh clues
and uncover a new secret

about the true extent
of the city's foundation.

Archaeologists,

investigating previously unexplored
areas around Machu Picchu,

discovered something surprising.

Contrary to long-held beliefs,

the terraces
weren't only built around the citadel

on the upper part of the mountain.

Their exploration work,
using LIDAR and 3D modelling,

allowed them to identify
and uncover new plots of terraces

in the lower part of the mountain.

From an engineering point of view,

we just have to stand back and say,
"That's really impressive."

By unlocking the secrets
of these iconic terraces,

experts have uncovered
the ingenious Inca engineering

that protects Machu Picchu
from the devastating threat of water.

But now, they face a new mystery.

Once the threat posed by water
was removed

how did the ancient engineers
meet the second challenge,

to conserve and exploit
this essential element for survival?

How did they supply a city, perched
at an altitude of 2400 metres,

with an uninterrupted supply
of water, for more than a century?

Solving this mystery is
the challenge for Alicia Fernandez,

an archaeologist
specialising in water.

This has been thought out.

Someone has actually
gone to this site and thought,

we need water to do this,
we need water to do this,

before we build anything.

This shows a level of planning
that you would talk about with

modern day megastructures.

Now, the source, which motivated
the construction of the city,

and supplied it with water
for over 100 years,

has been located
at an altitude of 2458 metres,

on the eastern side of the mountain.

A unique source,

which is at the origin
of an incredible hydraulic system.

The water system that
has been discovered at Machu Picchu,

shows that there was running water
all the time.

Following the terrain's
natural 3% incline,

the water from this unique source
was guided to the city built below

thanks to a series
of sculpted blocks of stone

just 10 to 12 centimetres wide.

This channelling system

allowed the city to be supplied with
150 litres of water every minute.

200,000 litres of water a day
for the citizens of Machu Picchu.

And the channels they've built,
they're capable of taking

twice the amount of water
that the springs can provide,

so they'll never be overwhelmed.

It was a way of maintaining a clean
drinking source for the people,

which enabled
the civilization to flourish.

Throughout the city,

there's this whole canalisation,

of channels, which
diffuse the water to outfall areas.

To distribute water around the city,

canal channels were branched
and multiplied into an immense web,

capable of supplying water to
the 17 fountains in the urban area.

The inhabitants of Machu Picchu had
access to fresh water all year round.

Enough to fulfil their needs

and to celebrate the sacred rituals,
which gave rhythm to city life.

To reach the urban areas,

the system of channels
also crossed the agricultural zone,

but it wasn't intended
to irrigate the land.

The agriculture there,
they had no form of irrigation.

They didn't need it.
They had the rain.

The gods would give them
all the water they wanted.

The more than 2000 mm
of annual rainfall in Machu Picchu

are enough
to have agriculture of corn here.

This channel is just for
providing water to the urban sector.

It just happened
that the source of water

is on the other side
of the Machu Picchu mountain,

and it has to cross
the agricultural sector.

The agricultural zone is made up
of the iconic foundation terraces.

Thanks to
the underground drainage system,

rainwater could irrigate
these terraces without flooding them.

A controlled flow of water
supplied the layer of fertile ground

and allowed for corn to grow.

Also, most part
of the agricultural sector

is directly oriented to the east,
to the sunrise.

In this way,

the terraces can capture
most of the sunlight during the day

and can generate a special
atmosphere at night for the crops.

In Machu Picchu,
they have worked in tune with nature

rather than against it.

It's genius, the system of not only
getting rid of excess water,

but equally, delivering
drinking water all year round.

Thanks to a mastery
of civil engineering techniques,

and a perfect knowledge
of their environment,

the Inca were able to overcome
the challenge set by water

and turn this threat into a strength

while maintaining the breathtaking
scenery that surrounded them.

But with the mountain
protected from landslides,

and a source of water located,
another challenge awaited the Inca.

The construction of the city itself.

At the peak
of the eponymous mountain,

the city of Machu Picchu, built
in the middle of the 15th century,

sheltered between
500 and 700 inhabitants.

With nearly 200 buildings,
and terraces carved into the stone,

it remains the best-preserved
urban creation of Inca civilisation.

Machu Picchu is actually
the most complete Inca site.

It is the most impressive living
testimony of Inca civilization.

When you are looking to locate
a city, a settlement, a community,

you're looking at trade routes,

you're looking at
lowest crossing points on rivers,

but in Machu Picchu, on top of a
mountain, that is something special.

We're still learning today
or theorising today

how they may have done it.

As an architect, I really wish
I can have a time machine

and go back in time
and see how they did it.

Without a time machine
or written testimonies,

experts attempting
to unravel the mystery

behind the construction
of these unshakeable walls

have to base their research

on archaeological
and geological excavations.

The first question is about
the origin of the raw material

used to build the city.

Where do these stones come from?

And how were they
transported to a site

so high up a steep-sided slope?

To answer this question,
geologists, like Victor Carlotto,

took an interest
in the site's topography,

as it was 500 years ago
when the Inca first arrived.

When the Inca
first discovered the site,

80% of its surface was covered by
these stunning geological formations.

To solve the mystery of its origin,

it is necessary to study it
on different scales.

First of all, on a microscopic scale,

this rock
revealed its nature to experts.

It is granite, a magmatic rock

originating
from the depths of the Earth.

Granite is an igneous rock.

It's a rock that comes
from the centre of the Earth

in a molten form.

But to understand
how this granite travelled

from the depths of the Earth
to the summit of this mountain,

we must take to the sky and
view the area on a satellite scale.

On this scale,
we can locate the citadel

in the heart of the Andes,

the longest continental
mountain range in the world,

up to 800 km wide,
stretching over 7000 km long

and peaking at an altitude
of 6900 metres.

It is the formation
of this impressive mountain range,

which is at the origin
of its specific geology,

known as 'granitic chaos'.

When the Andes were formed,

these granitic rocks
rose to the surface and broke apart.

During the formation of the Andes,
over 200 million years ago,

this magmatic rock formed at depth

and slowly rose
to the Earth's surface.

As it rose, it cooled and fractured.

Then, erosion
of the upper layers of the mountain

slowly revealed it at the surface.

As torrential rainwater seeped into
the gaps, it accentuated the cracks.

Due to gravity,
on this steep terrain,

the blocks finally separated,
fell, collided and piled up,

creating
the rocky heap of 'granitic chaos'.

discovered by the Inca
upon their arrival.

A disordered rock pile, giving
the site an uneven and rugged relief,

particularly
unsuitable for construction.

But the Inca of Machu Picchu

managed to profit from this
inhospitable geological architecture

by exploiting it as a quarry
to build the city.

It gave their buildings

the impression of being
a natural extension of the mountain.

Machu Picchu is fascinating
because of where it is located

and how the Incas
transform the mountain

with this organic architecture

that doesn't break nature,
but blends with it.

With the question of the raw
materials' origin resolved,

the next mystery

is about the construction
of these indestructible walls.

This natural granite quarry
offered the Incas

an ideal building material
as hard as concrete.

But how did they work with it?

How did they manage to cut it

when historians agree that the Inca
used neither tools nor machines?

Granite is a very hard material,

one of the most difficult materials
to actually shape, to work, to cut.

And yet, they chose
to build a city out of it.

Granite is a very,
very hard rock,

and it's usually worked with iron.

Without iron tools,

to actually shape these huge blocks
is just amazing.

Without cranes,
without machines as we have today,

this is an amazing achievement,
and probably unrepeatable.

Fernando Astete is the director of
the Machu Picchu archaeological park.

He has been studying the secrets
of this area for many years.

Now, he has developed a theory

that has become
widely recognised by his peers.

According to him, the answers to the
questions concerning cutting granite

can be found on the site.

And explained on a microscopic scale.

On this site, hematite,

natural iron oxide with a resistance
superior to granite, can be found.

According to Fernando Astete,

the Inca used hematite
as a natural hammer.

By banging the two rocks together

they could cut blocks, irregularly,
but with extreme precision.

The engineers
that were able to shape the granite

into such irregular forms

with such close bonding
between the different materials

is amazing.

But once cut, how
were these granite blocks assembled,

and fixed in place
so they wouldn't move for 500 years?

Once again,
Fernando Astete has uncovered clues

that help answer this question.

He's discovered a construction site
abandoned by Inca stone workers

and still visible today.

The site gives him
an incredible opportunity

to study the work methods
of Inca builders.

Once again, the use of 3D models

has complemented the investigators'
research and observation work.

It allows them to better visualise

the different stages
of ancient stone working.

To ensure that the granite blocks
fit perfectly together,

the Inca first selected a block
upon which they placed a wedge.

Then they placed a second block
on top of the first

and finished their cutting.

The Inca sculpted the surfaces
of the top block and bottom block

until they matched.

Once the shapes of the two surfaces
were harmonised,

the Incas took out the wedge.

The two blocks fitted together,

and stayed in place
without cement or mortar.

And mortar is there
to keep material apart

using a regular material
to create a level bed

so that you can
create vertical structures.

At Machu Picchu,
they threw away the mortar.

They didn't need it, because they
were so good at shaping the stones.

And these unusual shapes,
they're like a jigsaw.

They're all built to fit the hole.

There's virtually
no space in the joints.

You can't put a knife
or a piece of paper in there.

And now, in times of earthquake,

it's the buildings of the Incas
that survive

rather than the buildings
that were built 10 years ago.

They're all together working
as a unit, and that's their goal,

it's a unit moving all together.

The architect, Andres Adasme,

has been studying
the walls of Inca temples for years.

He wants to unravel their secrets.

One of these mysteries concerns
the resistance of these walls

to earthquakes
that regularly shake the region.

We have already
in the last 200 years,

two big ones, 1960 and 1650,
a long way ago, right?

But both, the walls are here,
just like the way it was.

In 1950, a terrible earthquake
devastated Cuzco,

80 kilometres from Machu Picchu.

The buildings, constructed
by the Spanish conquistadors

in the 16th century, crumbled,

whereas the Inca walls, built one
century earlier, remained standing.

Investigators
trying to unlock the mystery

of these invincible walls'
seismic resistance

have discovered new proof

of incredible civil engineering
techniques mastered by the Inca.

In the first layer,
in the first foundation,

they have small stones,
like circular, rounded stones.

And the idea
is that it works like a skate,

so it moves all together,
and it's not cracking.

Otherwise, if it's steady
and really strong,

it will crack with the earthquakes.

In this case, it's moving
as the earthquake is happening,

making the stones
support one with another,

and that makes that
it works all as one element,

right, moving like this.

The Incas were the best engineers
of their time.

They were on top of their technology
in their lifetime.

The main sources
for understanding the Incas

come from Spanish chronicles,

and there is still a lot of things
that we do not understand fully.

Little by little, over the decades,

through research
and technological progress,

from the heart of the city
to the depths of the tropical jungle,

the hidden mysteries of Machu Picchu
have slowly been unravelled.

And even if it still
has many more secrets to expose,

experts are far from running out
of leads in their hunt for answers.

The most unexpected one
is based on a mysterious system,

coded using tiny knotted ropes,

found in different places
over the Inca Empire, called 'khipu'.

A system currently being studied

thousands of kilometres away from
the sanctuary, at Harvard University.

It is here that a distinguished
American anthropologist,

and his student, are
on the cusp of deciphering it.

Up until very recently,
it was always believed

that it was record keeping.

But recent research
at Harvard University

is starting to demonstrate

that it's actually
a linguistic system as well.

The team of Gary Urton
has already been successful

showing us information
that was recorded on 'khipus'.

If they are able to decipher
or translate what it means...

then that would be a revelation.

Within these knotted cords,

we effectively could be looking
at the secret of the Incas...

the secret of Machu Picchu.

A secret, with a quest

which has motivated researchers
around the world for over 100 years,

and will undoubtedly
continue to do so for a long time.

Captions C SBS Australia 2020