All language subtitles for Ancient.Engineering.S01E02.The.Great.Wall.Of.China.1080p.AMZN.WEB-DL.DDP2.0.H.264-NPMS_track3_[eng]

- [Greg] We are surrounded

by extraordinary
feats of engineering

constantly pushing the
boundaries of what's possible.

- Without engineering,
there'd be no modern world.

- [Greg] Gigantic cities,
amazing infrastructure,

and ingenious inventions.

- Engineering is the key to
turn dreams into reality.

- [Greg] To reach
these dizzying heights,

today's technology
relies on breakthroughs

made by ancient engineers.

- It's mind-boggling
how they did this.

- [Greg] How did
early civilizations

build on such a scale?

- They raised the bar
for construction in a way

that no one thought possible.

- The sheer engineering ability,
which is a self-impressive.

- [Greg] By defying the
known laws of physics

and daring to dream big.

They constructed wonders of the
world from gigantic pyramids

to awe-inspiring temples
and mighty fortresses.

All with the simplest of tools.

- Can you imagine the skills
people would have needed

to build like this now?

- [Greg] Now, it's possible
to unearth the secrets

of the first engineers.

- They managed to
construct edifices

that has survived
the ravages of time.

- [Greg] And reveal
how their genius

laid the foundations for
everything we build today.

[dramatic music]

One type of engineering
has shaped the world

for at least 12,000 years.

Brick by brick.

The way we live has been
defined by the wall.

- Human civilization
is a product of walls.

- [Greg] Fundamental
to everything we build,

the genius of the wall
is often overlooked.

- Concept of a wall is simple.

It's a boundary, it's a barrier.

- [Greg] Without walls
there'd be no houses,

skyscrapers or churches.

Even the world's most
pioneering construction

relies on its walls.

Today, architects and engineers

are designing new types of wall

needed to build next
generation cities.

But the planet's greatest wall
was built in ancient China.

When this early civilization
took wall building

to epic proportions.

- The great wall of China

is one of the most incredible
engineering achievements.

- [Greg] 2,000
years in the making,

the great wall was built

with the blood and
toil of millions.

- The workers paid
a terrible price.

It was hell on earth.

- [Greg] Its purpose:
to protect the nation

against barbarian enemies.

- This was the stone dragon,
the chilling symbol of a nation

that refused to compromise.

- [Greg] But how did the
ancient Chinese build a wall

that spanned deserts, rivers
and even mountain peaks?

- They built a wall
on a knife edge

on the top of a mountain.

- It looks incredibly
powerful and impressive.

It's just amazing.

- [Greg] Could there be secrets

waiting to be discovered
within its very structure?

- People began to wonder if
there was something awful

hidden in the walls.

- [Greg] And did the great
wall ultimately caused

the downfall of the dynasty
it was designed to protect?

But this engineering masterpiece

was not the first
wall ever constructed.

It came after centuries of
architectural breakthroughs,

that began with the
dawn of civilization.

20,000 years ago, the world
was locked into an Ice Age.

At this time, humans still had
no need for walls or houses,

because they were always on the
move, struggling to survive.

- In the Ice Age,
life was really hard.

You've got extreme
weather conditions,

but you're moving
around that landscape

trying to make the most of
some really scarce resources.

So you're taking everything
you own with you,

you're trying to create
shelter wherever you go.

- All you have is basically
your wits to protect yourself

and the others around you
to help protect yourself.

- [Greg] Gradually
thousands of years,

the earth began to warm up.

The ice sheets slowly retreated.

The world blossomed.

In an area of the Middle East
known as the Fertile Crescent,

there were rivers,
natural springs, rich soil

and an abundance of
plants and animals.

For the hunter-gatherers
who lived here,

this was now a world of plenty.

- It becomes far easier
for people to survive.

You can stop and
stay where you are.

Life is less brutal.

- [Greg] The fundamental
nature of human existence

was about to change
dramatically.

After tens of thousands
of years on the move,

people started to farm the land.

And these farmers
needed permanent homes.

- So in places like
the Fertile Crescent,

we start to see the beginnings

of what we really
understand as urban life.

- [Greg] In place
of rough shelters,

the first fixed
structures appeared,

and even these early buildings

would reveal some incredible
engineering genius.

At the center of this
revolution was Jericho

in modern day Palestine.

Archeologists long believed a
muddy hill was that remained

of the Stone Age settlement.

But when they started
digging this site,

they made an
astounding discovery:

the remains of circular
houses with solid walls.

They'd found the
world's first city.

Incredibly, 10,000 years
ago, these Stone Age peoples

had already engineered something

that would become the building
block of global civilization.

- Bricks!

[brick crashing]

- [Greg] There are two key
ingredients for brick-making

and the Middle East
has each in abundance:

mud and sunshine.

- So bricks are
essentially made from clay.

Clay is a very fine-grained soil

that you can find pretty
much all over the world.

So it's a very easy material
to locate and to work with.

- [Greg] The
ancients molded clay

into rectangular blocks
and left them in the sun.

Drying made them stronger

and they could then be
pushed out in little units.

- And with this engineering
leap, the world changed forever.

Bricks were here to stay.

- [Greg] These individual blocks

were glued together with mortar,

making the first known walls.

- When you're
building with a brick,

what you're essentially doing

is taking the earth
beneath your feet,

finding a way of turning
that into a wall.

- [Greg] Humanity's 10,000
year love affair with a brick

is evident across the globe.

From the first
handmade mud varieties

to the mass produced
examples of today.

Down the centuries, bricks
have hardly changed.

- I think bricks are
absolutely amazing.

And the reason
they're much the same

over the history of building

is that they're all
broadly the same size,

and for a really good reason.

The reason that brick
is the size that it is,

is it fits in your hand.

- [Greg] The world
today produces

an estimated 1.5
trillion bricks a year.

Instead of some dried, modern
bricks are hardened in kilns

at over 1,800
degrees Fahrenheit.

Once fired, they become
as tough as rock.

Bricks keep homes cool
in summer, warm in winter

and to some they're
even beautiful.

- I love bricks!

I mean, what isn't there
to love about bricks?

I love seeing a brick building.

There's something
romantic about it.

- [Greg] The brick is
a timeless technology.

But the people that built
the first brick walled homes

had a shotgun store.

Their new shelters
could actually make
them more vulnerable.

As archeologists further
explored the ruins of Jericho,

they made another discovery.

Inventing the brick
was just the beginning.

- The thing about
stopping in one place

and expanding all the
things you can do,

like agriculture,
keeping cattle,

starting your first crops,
that makes you prosperous.

And if you're prosperous,
you need to defend that stuff

from the people that
wants to take it from you.

- [Greg] So early settlers

then made a second
great engineering leap:

creating a massive defensive
wall surrounding their town.

Jericho became the first
known walled settlement

anywhere in the world.

Its final wall was
over 11 feet tall,

visible for miles around,

a statement of power
and a warning to anyone

who wanted to attack.

- What the wall does is not
just make us safe and secure,

but it provides the
symbolism of that,

because the wall
defines this as home,

or this is my place, and
that is outside my home.

So human civilization is
literally a product of the wall.

- [Greg] With Jericho, the
defensive wall had arrived.

In the next few centuries,
great walled cities

sprang up across the region,

their defenses becoming ever
bigger, ever more complex.

Damascus, sitting at the
crossroads of Africa and Asia.

Uruk, ancient city
of Mesopotamia

and at the time
largest in the world.

Babylon, the sinful
city of the Bible,

famed for its huge
walls, hanging gardens

and mythical tower of Babel.

And Jerusalem, the Holy City,

lying just 19 miles
east of Jericho.

Methods may have changed,

but the construction of
defensive walls in this region

continues to the present day.

Standing between Jerusalem and
the ancient side of Jericho,

a very modern defensive wall:

the Israeli West Bank wall.

The Israeli government
call it a security barrier.

It divides their population
from the Palestinians.

- Walls are to a certain
extent a testament of fear,

because they are about
building something

to stop someone or
something from getting in.

- [Greg] Cutting through 440
miles of undulating land,

the West Bank wall is a
feat of modern engineering,

like it or love it.

It's made of concrete
slabs up to 26 feet tall,

bristling with
watchtowers and cameras.

At other points,
giant electric fences

supplemented by patrol roads,
razor wire, and trenches.

Modern walls can be built fast,

but for thousands of years
the defensive walls purpose

has remained the same:
keeping other people out.

Just a few hundred miles
away from this modern border

lies the home of a very
different civilization.

One that began its own
period of wall building

and construction
5,000 years ago.

[dramatic music]

Ancient Egypt.

- When it came to
building walls,

the Eguptians were brilliant.

- [Greg] Egyptian civilization
took building in stone

to another level:

jaw dropping palaces,
soaring pyramids,

and temples featuring
beautiful decorated columns.

- When it came to that temples,

in which gods were worshiped,

the Egyptians tended to
surround these temples,

which were built from stone,

with thick huge
walls of mud brick.

- [Greg] Solid walls
fortified the temples,

defining the land
within as sacred

and protecting the complex.

But in some cases,

there was something
highly unusual about them.

Bizarre undulating forms,

no other Egyptian
walls looked like this.

So was this
pragmatic engineering

or did it have a deeper purpose?

It's one of the great
mysteries of ancient Egypt.

In search of answers,
archeologists and engineers

make detailed
structural examinations.

Finding no engineering
explanation

for the undulating design,
historians had a brainwave.

- And there is the
school of thought

that this is meant to
replicate the waters of chaos.

- [Greg] Ancient
Egyptians believed

that the world was
born from the sea.

And archeologists now think

the wavy walls
reflect that myth.

But could there be another
reason why curvy walls

appealed to the
engineers of Egypt?

Neuroscientists at the
University of Toronto

may have come up
with an explanation.

After testing volunteers
in a brain imaging machine.

Participants were shown pictures
of internal architecture,

both curvy and straight edged.

Their brain scans revealed
a fascinating truth.

- So, as humans, when
we're viewing structures

that have very sharp lines
or sharp edges or corners,

it almost conveys threat.

Whereas curved lines, soft edges

much more comfortable
and welcoming.

- [Greg] This insight
could help explain

why most defensive
walls aren't curvy.

- So defensive walls are there

to not only physically
keep people out

but also to look
intimidating and domineering.

- [Greg] This may also explain

why many modern architects
are creating buildings

with curved walls.

The Guggenheim in Bilbao

with its dazzling curves of
titanium, limestone and glass

creating surfaces that ripple
in the change in light.

The Metropol Parasol, largest
wooden structure in the world,

like a giant mushroom springing
up in the heart of Seville.

And the National Museum of Qatar

with its interlocking discs

inspired by the
desert rose crystal.

Across the globe, a new
generation of iconic buildings,

abandoning the tyranny
of straight edges.

Their designs too
mathematically complex

to draw on paper,

created instead with
cutting edge 3D technology.

- What the computer
enables you to do

is to model not just the
design, not just the building,

but also how you're
going to construct it.

- [Greg] Working at the
limits of the possible,

this is high risk engineering.

- If you get it wrong,

it's not just that these
buildings will look bad,

it's that they simply
won't stand up.

- [Greg] These mind-bending
modern structures

are changing the
language of architecture.

but they're follow
in the footsteps

of an earlier
architectural revolution.

One that 2,000 years
ago to wall building

to a whole new level and set
out to build the impossible.

[dramatic music]

Ancient Rome.

Roman roads, bridges,
monuments and public buildings

were constructed on an
unprecedented scale.

And one leader would push
their engineering prowess

to the very limit, creating
one of the most extraordinary

defensive walls in history.

The emperor Hadrian.

- Hadrian, above all,
was a wall builder.

He was someone who wanted
to set the boundaries

of the Roman empire,

to divide what was Roman
from what was not Roman.

- [Greg] Hadrian came
to power in 117 AD,

inheriting the Roman
empire at its height.

It's stretched from the
sands of the Sahara desert

in North Africa, to the
rivers of Mesopotamia in Iraq

and northward to the Rhine
and Danube in central Europe.

But on the remote fringe
of this vast empire

laid one troublesome
province: ancient Britain.

- For the average
Roman infantryman,

the prospect of
traveling to Britain

would have been
absolutely terrifying.

- [Greg] The tribes
of ancient Britain

were not taking
occupation lightly.

- One of the defensive
tactics was to create displays

of hysteria, supposedly,
to really play up

the role of the barbarian,

and the Roman soldiers
were petrified.

- [Greg] One part of the country

proved particularly nerve
wracking: Caledonia,

modern day Scotland.

Faced with unruly locals

and the inhospitable
Caledonian landscape,

Hadrian came up with
a unique solution:

a gigantic wall like no other.

- Hadrian decided to
build what we now know

as Hadrian's wall,

which was to be a boundary,
but, but also a checkpoint,

a place where the Romans
could control movement

between what was their territory

and what was controlled by
the tribes north of the wall.

- [Greg] His plan would require
a massive defensive wall

studded with forts and towers.

It would have to be manned
by thousands of troops,

built across mountains,
valleys and rivers

running the width of
Britain, dividing the land.

The wall would begin at
the banks of the river Tyne

near the North Sea and
continue all the way

to the Solway Firth
on the Irish Sea,

cutting across the
country for over 70 miles.

For the Roman occupiers
far from home,

it was an incredibly
ambitious goal.

- Anyone who's visited
Cumbria or Northern England

will note it is a
spectacular landscape

but not the easiest to traverse.

- [Greg] Engineers
would have to deal

with fast flowing
rivers, hard rock

and mile upon mile
of rolling hills.

But where would they find
thousands of laborers?

- The hard graft of
the wall building

was all done by Roman soldiers
from three different legions.

- [Greg] 30,000
men were available

for wall building duties.

The Roman army spent very
much more of its time building

and making and putting
infrastructure in place.

- In the army itself, we don't
just have skilled fighters,

but also engineers,
surveyors, doctors,

chefs, people who made trumpets,

people who looked
after the animals.

It was a whole community.

- [Greg] Construction
began in 122 AD.

Soon, men from every legion
were hard at work on the wall.

Over 75,000 cubic yards of
stone was torn from the ground

and taken where needed.

Stonemasons dressed each stone
with hammers and chisels.

They were then set in place

by the hands of
the legionnaires.

Two columns were built
and the space between them

filled with a core of
rubble, earth and mortar,

and for added strength Roman
engineers had invented a way

to set their mortar rock hard.

What you do is you
take a limestone

and you roast it
at a temperature

anything between 900 to
12,000 degrees centigrade.

This drives out all the
moisture, creating quicklime.

- And what you can
do with quicklime

is you grind it into a powder,
you can slake it with water,

and then what you had in
essence is a form of concrete.

- [Greg] The Romans used
this super tough concrete

to lock stones together.

And it's still in evidence
in some parts of the wall

nearly 2,000 years later.

[sheep bleating]

[gentle music]

And the wall today
holds other secrets,

carved into its fabric.

- We know that Roman
soldiers built the wall,

because they left
their signatures on
some of the stones.

We have the names of the legions
who were stationed there.

Sometimes we have the emblem

for the legion as
well, their identity.

- [Greg] But how did
the Romans ensure

their mighty fortification

would succeed in
its intended job?

Only monumental
engineering could hold

the so-called barbarians.

The main stone wall
stood almost 10 feet wide

and nearly 20 feet high.

Small forts built into the
walls a Roman mile apart

housed 32 soldiers.

And two stone lookout turrets
were placed between each fort.

Any sign of trouble

and reinforcements could be
deployed rapidly along the wall.

14 much larger forts were
also built next to the wall.

- A purpose was to
fortify the wall.

Soldiers would be
stationed in these forts

to keep control over who
was passing through the wall

to keep watch at who
might be approaching.

And so that they
could send signals

to assemble a field
army if necessary.

- [Greg] Hadrian's wall was
a huge statement of intent.

- To the local tribes,
this would have been

a powerful expression
of Roman dominance.

This was a structure
which sent the message:

We're here to stay.

- This is something alien.

This is something brutal.

And this is something that's
been designed to control us.

- [Greg] But massive walls
weren't the only deterrent

in Rome's arsenal.

The occupiers also engineered
small-scale defensive weapons

that were surprisingly
effective.

And in the soil beneath
the imposing battlements,

archeologists discovered a
piece of Roman engineering

so simple, yet so devastating

that it's design is
still in use today.

The caltrop scattered
on the ground.

Its sharpened edges can
lame a soldier or a horse.

Modern equivalents are now used

to take on horsepower
of a different nature.

Deployed by armies and police
forces to disable vehicles.

[helicopter buzzing]

For the Roman military forces,

the ability to stop the
enemy was equally important.

Thanks to their
incredible manpower

and engineering prowess,

Hadrian's wall was
completed in 128 AD.

It had taken just six
years to construct.

Hadrian's wall served as
the Northwest frontier

of the Roman empire
for 300 years.

At its peak, more
than 10,000 men lived

and worked here
as border guards.

Today the wall is a
world heritage site,

recognized as a landmark
in military engineering.

It's rumored that
Hadrian's masterpiece

was inspired by word of an
even bigger defensive wall.

One being built in
a mysterious kingdom

thousands of miles
away from ancient Rome.

China.

Today at the forefront
of engineering,

over the last 30 years China
has transformed itself,

rebuilding infrastructure
on a massive scale.

- Modern day China is a
huge engineering project.

- [Greg] 60% of the population
now live in urban areas,

including six of the
world's mega cities.

The Three Gorges Dam
is the world's largest

and possibly the greatest
single engineering project

of the 20th century.

This manmade mountain
took wall building

to record breaking heights.

Standing nearly 600 feet
tall and 1.4 miles long,

it required 988 million
cubic feet of concrete

and 463,000 tons of steel,

enough to build
63 Eiffel towers.

Other gigantic
engineering projects

include the fastest
supercomputer, highest bridge,

and the world's largest
high-speed rail network.

China is a civilization
on the move.

- They find out how to
remove the barriers.

They don't let things
hold them back.

They will advance
and keep developing

and keep pushing the boundaries.

- [Greg] Groundbreaking
engineering

is in the country's DNA.

China first became a unified
nation 2,000 years ago

and almost immediately embarked

on the legendary
engineering project.

One that defines the
nation to this day.

The Great wall of China, the
most astonishing fortification

ever seen on earth.

It's so long.

The guards at the
eastern end of the wall

would witness the sunrise
one hour and 20 minutes

before guards at
the western end.

This gigantic stone
dragon is an iconic image

recognized through the world,

and even from space.

- The great wall of
China is undoubtedly

one of the great sights
of the whole world.

As a work of architecture,
it's extraordinary

and a work of engineering,
it's extraordinary.

- [Greg] The story of
wall begins in 221 BC.

China was a newly unified
country and under attack.

- To the north of China were
a nomadic group of people

known as the Xiongnu.

- [Greg] The so called
barbarians lived
in the mountains

and the plains of what
is today Mongolia.

They regularly crossed
into China, raiding farms

taking food and goods by force.

[riders yelling]

- These nomadic warriors
work famous for their use

of bow and arrow and also
for their horsemanship.

So they were renowned for
their lightning fast attacks.

It would have been
absolutely terrifying

being attacked by them.

- [Greg] With a huge
border to defend

and unable to mount
a military response,

emperor Qin came up
with an audacious plan:

to keep the enemy
out with a wall,

a wall thousands of miles long

to be built across
extreme terrain,
deserts, high mountains,

plunging valleys and rivers.

Only a madman would contemplate
such a feat of engineering.

But the emperor Qin had
the resources of an empire

at his disposal.

- He was one of the most
powerful autocrats in history.

- He was the most ruthless
of the most ruthless.

[dramatic music]

- [Greg] Nothing
would stand in the way

of the emperor's dream of
the biggest wall of all time.

Especially, when it came to
assembling a huge workforce.

- Well, the most forced
labor, ordinary people,

were taken from
the heart of China,

and criminals also sent
off to the great wall.

- More than 200
crimes were punishable

with laboring on the wall.

And if someone died
during their sentence,

one of their family members
had to take their place.

- [Greg] For the next 10 years,

more than 3 million
soldiers, peasants,

prisoners, and laborers were
forced to build the wall.

They started in the barren
lands of the Gobi desert.

Here, there was little
stone to be found

for hundreds of miles.

So engineers had to find

a different material
for construction.

For centuries Chinese farmers
have been building walls

out of rammed earth to
protect their homes.

Working in large groups,
they create a wooden frame

and then fill the space with
a mixture of earth and reeds.

They then ram the earth down
using tools or bare feet.

Engineers call this
downward force compression.

Pressure packs the earth
together, making it very strong.

Workers then added another
layer and continued the process,

building ever higher until
the wall stood 20 feet tall.

The finished earth and
structures were so tough,

that section still stand
in the desert today

more than 2,000 years later.

- Now, if you came galloping
in across the Gobi,

you would have seen a wall

such as no one had seen
the history of Asia,

and perhaps in human history.

- [Greg] Beyond the
desert sections,

walls erected by
farmers already stood

along some of the route.

- So the Qin emperor, he took
these sections of old wall

which already existed, and
he built new sections as well

to create a single
unified barrier.

- [Greg] As the wall
snaked on through valleys

and across mountains,

Qin's engineers used
whatever materials

they could get their hands
on: stone, earth or wood.

The Chinese people
paid a terrible price

for their emperor's vision.

It's been estimated that more
than 400,000 died of disease,

malnutrition or exhaustion.

The wall stretch from Lintao

into deserts of Northwest China,

to the banks of the Yellow River

and onto the steps
of inner Mongolia,

ending in the Northeastern
region of Liaodong.

A truly formidable defense.

Emperor Qin's wall was
known as the Long Wall.

It wasn't finished
in his lifetime.

It would take hundreds of
years and a twist of history

for it to become the
Great Wall we know today.

Emperor Qin died in 210 BC.

In life he ruled
with an iron fist.

And it turned out he planned
to do the same in death.

In 1974, workers unearthed

another incredible
construction project:

thousands of life-sized
warriors made of clay

ready to fight for the
emperor in the afterlife.

The terracotta army.

Like most walls,
emperor Qin's Long Wall

was built to keep people out.

- Throughout history
walls have been built

as a defining point to say: on
this side, we are civilized,

but on that side, you are not.

- [Greg] But perhaps the
most famous modern wall

was created to keep people in.

The Berlin wall.

It's purpose to stop East
Germans escaping to the West.

In the early hours of
August the 13th, 1961,

East German construction workers

backed up by soldiers and police

began erecting barriers
throughout Berlin,

dividing the city
street by street.

What began as barbed
wire and fences

evolved into a sophisticated
reinforced concrete wall

with watchtowers, kill
zones and minefields.

Guards were ordered to shoot
anybody who tried to escape.

For 28 years, the wall stood

as a symbol of the Cold
War, dividing Europe.

Until the 9th of November, 1989,

when thousands of demonstrators
marched on the checkpoints,

forcing overwhelmed
guards to open the gates.

Rejoicing crowds poured
into West Berlin.

Revelers danced on top of
the wall and demolished it.

The years of
separation were over.

The Berlin wall had fallen.

A reminder that throughout
history regimes come and go.

And in the year 1368,

a new regime was taking power
in China, the Ming dynasty.

And they would push Qin's
architectural legacy

to the next level.

- China really changed
under the Ming dynasty.

- [Greg] The Ming were a
modern, outward looking dynasty

sending trade missions abroad
and selling their silk,

brocade and porcelain.

This trade brought
them great wealth.

Before they tackled
the Great Wall,

the Ming first chose to
stamp their identity on China

with another extraordinary
construction project:

the Forbidden City, the
emperor's new palace.

10 years in the
planning and built

with some of the most ingenious
engineering techniques

of all time.

- It was a palace
unlike any other

that had ever been
built in China.

And it was a real statement

that the man living in
the middle of this palace,

the emperor, was
the son of heaven.

- [Greg] But like many
cities around the world,

the Forbidden City was built
on a geological fault line.

- Earthquakes are a
really devastating force

that gets applied
to our structures.

It's a large force.

It's chaotic, that often
very unpredictable.

- [Greg] And while modern
engineers seek ways

to defend their buildings
against earthquakes,

it seems they have much to learn

from their ancient
Chinese equivalents.

The Forbidden City has
been hit by over 200 quakes

and survived them all.

Present day architects
wanted to learn how.

Researchers examined
the wooden buildings

and discovered the answer lay
with their complex carpentry.

Wooden beams and columns
formed the structural core

of all the forbidden
cities buildings,

and between their crossbeams
and roofs are ornate brackets.

They're made of interwoven
beams and blocks.

None of them fixed.

They support the eaves and roof,

and sit on a large beam
supported by tall columns.

But the columns
are free standing.

All these structural parts
bear the roof's immense weight,

but nothing is fixed
glued or nailed.

So when quake strikes, all
parts are free to move.

- They figured out how
to allow the buildings

to rock in an earthquake
without breaking.

We're now fully
understanding how that works.

- [Greg] The forbidden
city was built

to survive natural disasters,

but there's another secret
hiding within its walls.

The flashy show palace
doubles up as a fortress

defended by soldiers.

33 feet high defensive walls,
a moat, and watchtowers.

Walled cities may no longer
have a role in the modern world,

but even today the most
important buildings

are still designed
with security in mind.

One of the most recent is
the U.S. embassy in London.

- It's been designed to
look open, transparent

and be a symbol of equality.

- [Greg] $1 billion
buys a lot of subtlety.

- [Alex] It looks lightweight.

It looks very soft
and almost delicate.

- [Greg] But don't be fooled.

The glass is blast proof.

The interior is solid concrete.

And the embassy boasts all
the latest defense systems,

including a 100 foot blast
zone, defensive ditch,

hidden steel and concrete
bollards, even a moat.

Inside, there's a
barracks for soldiers,

anti surveillance technology,
and a fully staffed hospital.

The pursuit of security would
also lead the Ming dynasty

to a groundbreaking
engineering solution.

One that would go
down in history

as among the most amazing feats
of construction of all time.

- Although the Ming
dynasty was looking outward

as much as possible,

there was still a problem
with the Northern border.

- [Greg] In the 15th century,

China's old barbarian enemies

were threatening the
nation once again.

And sections of the
emperor Qin's ancient walls

were now crumbling.

- The Ming dynasty decided
to rebuild the wall

to firm up that boundary
between China and the North.

- [Greg] The Ming aimed
to create a huge new wall

thousands of miles long.

It would be manned by guards

and dotted with
towers and fortresses.

This time their
engineers would use

the same basic building block,

first created thousands
of years earlier:

in the wall cities of
the ancient Middle East.

- The wall was
built out of bricks

and they created
these enormous kilns

to create those many,
many thousands of bricks.

- [Greg] But no
brick is effective

without a good mortar.

And for this, the Chinese
had a secret weapon.

- So I've read that they
use sticky rice in there,

which is not something
you would see

on a materials list today.

- And the reason we
believe that that was done

is because the starch
and the sticky rice

gave the mortar a little
bit of flexibility,

so that when the
wall was experiencing

the temperature
variations it did,

it just allowed that
little bit of flex,

so that you wouldn't
get any major cracking.

- [Greg] This mixture
of clay, lime and rice

was so strong, it's
still bonding many
of the bricks today.

The wall was an epic
production line of quarrying,

stone cutting, brick
making and construction.

And it was brutal.

Some sections ran
across mountain ranges,

angles as steep as 70 degrees,

before plunging down
into deep valleys.

- It's incredible.

You can hardly walk
or climb up there.

You'd need ropes to hang on.

And yet they've built a wall

on a knife edge on
the top of a mountain.

So the people who did this,
they were incredibly brave.

And it's an amazing
piece of engineering.

- [Greg] Solutions to
these physical challenges

came from an expert in
an entirely different
field of study.

Liu Hui was one of the
greatest mathematicians

of ancient China.

He wrote a book that solved
complex engineering problems,

such as how to calculate
the depth of a ravine,

the width of a river or
the height of a building.

Using these instructions,

an army of engineers
plotted the course

and construction
of the Great Wall

and one simple but effective
bit of Chinese engineering

helped get their equipment up
the steep and narrow paths.

It is believed the Chinese
invented the wheelbarrow

somewhere around 200 AD,
and it remains in use today,

a staple of the
modern building site.

But other aspects
of wall construction

were far removed from
the modern world.

The Ming weren't big
on health and safety.

- The building work would have
been incredibly difficult.

We know that they suffered
badly from lack of clothes.

And we know they also suffered
badly from a lack of food.

And yet, the wall still
managed to be built.

- [Greg] Thousands of people
died building the Ming wall

and the horror of the work
gave rise to superstitions

that persist to this day.

- It's no surprise that
myths and legends of grownups

suggesting that the ball may
have actually been packed

with the bodies
of dead laborers.

- [Greg] Some
stories, even claim

the famous white rice mortar

was actually made from
the bones of workers.

Generations lived
and died on the wall.

It was a building project that
took 200 years to complete.

- So the Wall still stands today

as a magnificent
engineering achievement

but there's a shadow here,

because it could never
have been constructed

without the deaths of
thousands of Chinese people.

- [Greg] The world's
greatest defensive wall

begins in the East, on the
edge of the Gobi desert

at Jiayu Pass.

From here it runs through
mountains and across rivers

to the Shanhai Pass and the
coast of the Yellow Sea.

When finished, it was
patrolled by a huge army

occupying 25,000
watchtowers and garrisons.

If attacked, they send
smoke signals by day

or fire by night.

And the wall would
become a highway

bringing reinforcements
into battle.

But despite this extraordinary
engineering triumph,

the Ming dynasty fell in 1644.

The cost of building
and maintaining the wall

contributed to an
economic crisis.

The rebel army of
peasants angered by
poverty and starvation

stormed the capital.

- Historians believe that
the wall was actually crucial

to the collapse of
the Ming dynasty.

So expensive was it to
build and then to maintain

and to man with soldiers,

that it led to financial
and strategic collapse.

- [Greg] Shortly afterwards,

an army of Mongols
from the north invaded

and took over China.

The very people the wall
had been built to keep out.

It may not ultimately
have succeeded,

but the Great Wall of China is
a landmark in human history,

almost incomprehensible
in scale.

But it was never one wall:

different emperors added
to it across 2,000 years.

And in fact, it's precise length

has been something of
a mystery until now.

After a five-year
survey measuring

all known sections of the wall,

the Chinese government announced
that the official length

of the Great Wall of China
is just over 13,170 miles.

- The Great Wall of
China stands as testament

to those extraordinary engineers

but also the people
who had the vision

of creating a wall to
defend an entire empire.

[dramatic music]

- [Greg] The need for protection

is as old as
civilization itself.

Defensive walls first
appeared 10,000 years ago,

built around the
earliest cities.

The Romans went on
to supersize them.

And they reached
their absolute peak

with the Great Wall of China.

Many still stand today,

their construction involved
thousands of workers,

overcoming enormous challenges,

learning to build ever
more complex structures,

ancient engineers paving the
way for the modern world.

[dramatic music]