All language subtitles for Ancient.Engineering.S02E09.1080p.AMZN.WEB-DL.DDP2.0.H264-chr00t_track3_[eng]

[reverent music]

- [Narrator] The world's
greatest structures

push the boundaries
of engineering,

all fueled by a constant
desire to innovate.

- Without engineering, there
would be no modern world.

- [Narrator] Gigantic buildings,

complex infrastructure,

and ingenious inventions.

- Engineering is the key that
turns dreams into reality.

- [Narrator] Many of today's
incredible achievements

rely on breakthrough
technologies

first devised by
ancient engineers.

- It's astounding how
they achieved this.

- [Narrator] Early civilizations

built on an unimaginable scale

and with incredible precision.

- The raised the
bar for engineering

in a way that no one
thought possible.

- These are some of the
finest engineers in history.

- [Narrator] Redefining
the known laws of physics

and dreaming up the impossible,

they constructed
engineering wonders,

from colossal stadiums
to mighty waterways

and complex machines, all
with the simplest of tools.

- You can not imagine the skills

people would have needed
to build like this.

- [Narrator] By
unearthing the mysteries

left by these ancient engineers,

we can now decode their secrets-

- That so many of their
creations still survive

is testament to their
engineering prowess.

- [Narrator] And ultimately
reveal how their genius

laid the foundations for
everything we build today.

[reverent music continuing]

Nothing has defined
human existence

like our relationship
with water.

- Water is essential
for humanity

and always has been
since ancient times.

We all need to drink it.

We can't survive without it.

- Agriculture is the
most important part

of modern civilization.

Water is the key to that.

- [Narrator] And waterways
have played a vital role

in the development of cultures
and the growth of societies.

- You can't underestimate
the importance of waterways.

They've united empires,

they facilitated the
movement of people and goods

all over the world.

- These great civilizations
achieved their prosperity

because of their control of
great waterways and canals.

- [Narrator] Since
ancient times,

engineers have invented
ways to exploit water

for human benefit.

- We all owe ancient
engineers huge thanks

for their work in
mastering water

to allow us a way to navigate,

to transport goods,
and to build economies.

- [Narrator] And where
land didn't exist,

we've even created it on water.

- Nothing could stop these
ancient engineers dreaming big.

- [Narrator] But water is
also a destructive force

we've had to overcome.

- We've had to engineer
ways to protect ourselves

and our homes from
this enormous power.

- [Narrator] Pioneering
structures like Palm Jumeirah

and the Burj Al Arab
prove there are no limits

to our creativity in
building on water.

- So, this is harnessing water

using the most advanced
modern engineering.

- [Narrator] But how
did ancient engineers

first unleash the
potential of waterways?

[gentle music]

The first manmade waterways

were built for
transporting water itself

in one of the world's
earliest civilizations:

ancient Mesopotamia, a land
situated on the floodplains

between two great rivers,
the Tigris and Euphrates.

From the 5th millennium BC,
it's southern half was home

to one of the most innovative
societies in history,

the Sumerians.

- Ancient Mesopotamia
has often been described

as the cradle of civilization,
the Fertile Crescent.

This was an area
where agriculture

was first developed
in the Near East.

- [Narrator] But to reap
the land's full potential,

the Sumerians faced a challenge.

- Mesopotamia, a
large part of which

now falls within
modern-day Iraq,

is essentially large landmass.

It's incredible fertile,

but outside the banks of
the river it was very arid.

And when the water did come,

it more often came in the
form of flash-flooding.

- When there was too much water,

that devastated their farms,

so they needed to
be able to control

the amount of water
going into their fields.

- [Narrator] As a result,

they developed ways to
control these floods

and maximize the potential
of the two rivers.

- The Sumerians were
master engineers.

They knew how to
survey their land

and they built huge
levees or dikes

of earth, reed, and mud bricks,

which allowed them to build
huge, strong structures

to hold back water.

- [Narrator] To divert it
to where it was most needed,

the Sumerian engineers
designed channels

for the purposes of irrigation.

- And it's in this
process of digging

and casting up of
earth that they create

a really very complex
system of canals.

This is almost certainly

the first canal
system in the world.

- [Narrator] But the real
mastery of the Sumerians

was in how they
controlled the flow

of such a precious resource.

- So, the Sumerians were
incredible basket weavers.

Reeds grow naturally in
the Euphrates-Tigris area.

So, reeds themselves
are quite weak,

but the way that they were
interwoven in a complex way

created a material
of great strength.

That could be used to make
dams, sluices, boats, or houses,

but especially was
used in irrigation.

- [Narrator] When closed,
sluice gates woven from reeds

would prevent oversaturation
of the farmland.

To water crops, they
would be opened,

diverting water
either to reservoirs

where it could be stored

or into smaller canals
which led to the fields.

- In many ways, what they
did is turn a very arid

and inhospitable
land into what is,

in essence, an earthly paradise.

- [Narrator] And to ensure
these gates and canals

did not leak, the Sumerians
used an ingredient

that was in plentiful supply...

Bitumen,

a form of crude oil which
occurs naturally in the ground

across many parts
of Mesopotamia.

And the Sumerians made good use

of one of its
valuable properties.

- Bitumen is a thick,
oozy, sticky, viscous oil

and the fantastic thing about
this is it's hydrophobic,

so it literally repels water.

It doesn't mix with water.

This meant they could waterproof
their irrigation systems,

everything from their
sluices, their weirs,

their canals, and their dikes.

- If you could
waterproof your canal,

you're in much greater
control of the entire process

and you reduce the amount
of water that you lose,

something that was crucial
in the middle of the desert.

- [Narrator] The
ability to harness water

not only secured a food
supply through irrigation

but also allowed the
movement of goods and trade

and expanded the
Sumerian economy,

which in turn allowed a
rich culture to blossom.

- Alongside these
irrigated fields,

the Sumerians
built great cities,

huge, large structures.

A central feature would
often be the central temple,

the ziggurat.

These complexes would have

tens of thousands of
people living within them.

And with this form of
complex urban life,

we see a beginning of writing

in order to keep a
bureaucracy going.

They really were the
first cities on Earth.

- [Narrator] Through their
expert control of water,

the cities of Sumeria
grew to become

the most sophisticated
of their time.

But the rise of another
great ancient civilization

was powered through its ability

to better navigate its
most important river.

[pensive music]

The Nile,

ancient Egypt's central artery.

- I think it's very
difficult to overstate

just how important the
Nile was to ancient Egypt.

Without it, there would
be no Egypt at all.

- [Narrator] The only
source of fertility

in this desert land,

which the Egyptians also
controlled through irrigation.

- So, Egypt becomes
this sort of machine

for producing food

and it allows for a
population to flourish.

- [Narrator] But the
Nile had a problem.

While it was mostly navigable,

in several places to the south,

it was partially blocked
by massive patches of rock,

known as cataracts.

- Cataracts are
stretches of the Nile

which are really treacherous
to navigate through

on account of the
fact that the riverbed

is so close to the surface

and you've got lots
of exposed rocks.

- One way of navigating
the cataracts

was to take boats onto the land

and then haul them along and
then drop them back down again

at a point at which
the river is navigable.

- This wasn't just a few feet,

it was often several
hundred feet,

and the cargo was
often very heavy

and the boats themselves
very cumbersome.

So, for their society, their
prosperity, their culture,

it was essential that
they found a solution.

- [Narrator] There's evidence
that in the 3rd millennium BC,

Pharaoh Merenre
I had cut a canal

through the rock and
stone of a cataract

using sheer manpower
and determination.

Using their skills as
master stonemasons,

succeeding pharoahs
used these same methods

to carve more canals.

- They were prepared to
go to what seemed to us

to be extraordinary lengths
to achieve their ends,

and that meant even
manipulating the course

of one of the
world's great rivers.

- [Narrator] A few hundred
years later in around 1870 BC,

Pharaoh Senusret III
invented a faster

and less labor-intensive method.

He would build a
slipway on the riverbank

and slide his boats
around the cataracts.

- Imagine railway sleepers
with wooden tracks laid on top

greased with river mud,

which allowed those
boats to be dragged.

- [Narrator] Around 10 feet
wide and over a mile long,

the slipway was supported
on both sides by bricks.

Wooden beams then ran across
it like railway sleepers,

while river mud created
a gently-sloped base

to support the boat and help
it slide along more easily.

- This was still no easy task.

It would have taken an
immense amount of muscle power

to move those boats
just a few feet.

But now the Egyptians
could transport materials

in either direction.

- And that allows them
to band their territory,

expand their control
of the region

and its resources even further.

- [Narrator] By finding
ways around the cataracts,

Egypt's pharoahs
were able to extend

their country's southern border,

opening up trade with
the rest of Africa

and making the Nile one
of the most efficient

inland waterway
systems in the world.

- I think it's a testimony
to just how powerful,

capable, and determined
the Egyptians were.

- [Narrator] In the modern era,

manmade waterways have
revolutionized global trade,

exemplified by the Suez Canal.

An engineering triumph
completed in 1869,

it cut through a
75-mile-long stretch of land

connecting the Mediterranean
with the Red Sea

and halved the journey time

for vessels traveling
between Europe and the East.

- The Suez Canal
was the first canal

to be built right
through a country

and to be accessible
to all nations.

- [Narrator] Today, nearly
20,000 vessels a year

travel along the Suez Canal,

transporting cargo worth
in excess of $3 trillion.

Just how important this canal
is became clear in March 2021,

when a cargo ship
called the Ever Given

was blown off-course
by sideways,

completely blocking the
route for other traffic.

- And although it was
only blocked for six days,

this had a ripple
effect across the world,

affecting global
trade for months.

- [Narrator] Proving
just how vital

manmade waterways still
are to our modern world.

But in ancient times,
canals were so important

they could even become the
means of uniting a vast empire.

China, one of the world's
oldest civilizations.

Like many other cultures,

China's earliest settlements
grew up alongside its rivers.

- The northern frontier of China

was against the great
grasslands of Central Asia.

This presented a
continual military threat

to the settled
agricultural communities

of southern and central China.

So, how do you get the grain

needed to feed the
army to the north

when it's all being
grown in the south?

- [Narrator] Most of China's
great rivers flow west to east,

with very few natural
connections joining them.

This meant there was no easy
way to travel between them.

To overcome this, the Chinese
built a series of canals

traveling north to south across
China's five major rivers

that would become known
as the Grand Canal.

Built in sections over
hundreds of years,

it would eventually span a
length of over 1,000 miles.

- The first canal, built
in the 5th century BC

between the Yangtze
and the Hubei Rivers,

was constructed
by the Wu kingdom

in order to transport troops

and particularly
food and supplies

to protect their
northern frontier.

- [Narrator] And as
subsequent dynasties

expanded their territories,

they also built
sections of the canal.

A thousand years later,
in the 7th century AD,

leaders of the Su Wei dynasty

had the visionary
idea to connect all
these smaller canals,

creating one vast waterway.

Built entirely by manual labor,

this monumental task
required a workforce

only an emperor could enlist,

but this would come
at a huge cost.

- The emperor, Yang, mobilized
about five million people

it's been estimated
would have been employed

in constructing
this grand canal.

- By any standards, this is
an amazing engineering feat,

but I don't think we
should underestimate

the cost to human life
because the conditions

within which these people
were working were truly grim.

- [Narrator] Over the
following centuries,

the route of the canal
was further developed

to resemble its
current course today.

Extending for over 1,100 miles,

the Grand Canal was the
longest manmade waterway

in the world.

It stretched from the city
of Beijing in the north

to Hangzhou in the south,

the equivalent of the distance
between New York and Miami.

- This was the world's largest,

most extensive civil
engineering project

that anyone had ever seen

prior to the
Industrial Revolution.

- [Narrator] But as the
canal grew in length,

this disparity between
the water levels

of the connecting rivers
became a major obstacle.

- One of the big
engineering challenges here

is that this enormous
water network

is joining together
five different rivers

that were all at
different heights.

So, how do you join waterways

when you've got a height
difference to contend with?

- So, what the canal needed

was a system of moving
uphill and downhill,

and this came in the form of
really quite rudimentary locks.

- The earliest
invention of the lock

was called a flash lock.

It was created
with just one gate

and it would hold back the
water, keeping a vessel high.

It would open, and then the
vessel would travel downstream

with that flow of water.

- [Narrator] A flash lock was
a narrowed section of canal

with a navigable gap.

Planks were slotted into grooves

in two vertical wooden poles

embedded on either
side of the riverbank

to form a wall that could
dam water behind them.

Once a sufficient level
of water had built up,

the planks were quickly removed,
releasing a surge of water,

carrying the vessels
downstream and over any rapids.

But going upstream
still required manpower

to physically winch or drag
vessels to higher levels.

This was fine for smaller boats,

but larger vessels were
prone to getting stuck,

especially on steeper gradients.

So, some expert believe
that Chinese engineers

of the Song dynasty
in the 10th century

found a revolutionary solution.

- So, the big innovation came

with the invention
of the pound lock.

- [Narrator] To raise
or lower a vessel

between stretches of
water at different levels

required an enclosure
to be created

by the introduction of
an upper and lower gate.

Wooden planks are set into
grooves in the upper gate

to dam the water ahead
at the higher level.

As a boat enters, the lower
gate is closed behind it,

creating an enclosed
pound or chamber.

Water is allowed to
flow into this chamber,

raising the level
along with the boats.

Once the water level is the
same as the river ahead,

the remaining upper gate planks

are removed by a
rope and pulleys

and the boats carry
on their journey.

- This meant that not
only could it better deal

with different heights of water

but you could also travel
in either direction.

- [Narrator] The pound lock
was a revolutionary invention

and one that's still in use
today all over the world.

This was the piece of the
puzzle that allowed boats

to be able to reach
any part of the system.

The Grand Canal became the
backbone of the empire,

not only facilitating
the easier transporting

of goods and troops

but also providing a
link between the peasants

and the Imperial Court,

helping them to create and
control a more unified China.

- This engineering endeavor,

I think it's one of those feats
that almost defines a people

and defines a culture.

- [Narrator] Although
sections of the Grand Canal

have fallen into disuse,

China still has the most
extensive waterway system

anywhere in the world,

with over 75,000 miles of
navigable rivers and canals.

[pensive music]

Where the Grand Canal's locks

allowed rivers of varying
heights to be connected,

in recent centuries canal
locks have also been used

to connect oceans, each
with differing tidal ranges.

- The Panama Canal is
a 51-mile-long waterway

connecting the Pacific
and the Atlantic.

It's huge in its scale.

And when it opened in
1914, it was innovation

at the very peak
of what humanity

thought they could
achieve at the time.

- [Narrator] It was
one of the world's

greatest-ever engineering
works, saving ships the lengthy

and often treacherous
trip around Cape Horn,

the southernmost tip
of South America,

opening coastal shipping routes
to the American West Coast.

- The challenge with the
terrain for the Panama Canal

was that it wasn't flat;
it was mountainous.

Instead of building a trench,

which would have been incredibly
time and labor intensive

and cost a huge amount of money,

they lifted the vessels
up by creating locks

that would allow the vessels

to go over the
mountainous terrain.

- [Narrator] Connecting these
two vast bodies of water

presented one of the greatest

engineering challenges
of the time:

how to bridge the
85-foot height difference

between the two
oceans and Lake Gatun,

the body of water dividing them.

The only way to raise
the ships high enough

to reach the lake was to create
a series of massive locks.

- The engineers built
a series of three locks

on the Atlantic side that
would lift the vessels up

the 85 feet to the Gatun Lake.

At the highest point,
they did channel through

the most mountainous section.

And then on the Pacific side,
they had another three locks

that would lower
the vessel down.

- [Narrator] And to ensure
the canal was protected

from the Pacific's
strong currents,

the engineers devised
another solution.

- They designed
these V-shape locks,

entirely different
from the Atlantic side.

These V-shape locks were
huge, massive steel gates,

730 tons, and they
were vastly deep,

but this allowed
them to mitigate

against the volumes of water
and the changing tidal range.

[water rushing]

- [Narrator] The lock
gates close in a V shape

with the tip upstream

so the force of the water from
the upper side secures them,

keeping the mighty
Pacific Ocean at bay.

- The fact that they were
V-shaped was very important

because that V resisting the
hydrodynamic pressure here

actually, in a way, wants to
close the gates even more,

so they fail safe.

- [Narrator] Thousands
of workers were employed

over the course of a
decade to carve these locks

out of the difficult
mountainous terrain

using heavy machinery
and dynamite,

with the tropical climate

significantly adding to
this challenging work site.

Today, the canal sees around
13,000 to 14,000 ships

pass through it every year

and hundreds of millions
of tons of cargo,

providing a reliable passageway
between opposing oceans.

[reverent music]

Both natural rivers and manmade
canals can be vital conduits

to the growth of cities
and civilizations,

but harbors have also
played an important role.

- Since ancient times,

sea harbors have been
crucial waterways

because they enable
different cultures

to interact through trade

and also provide a base for
navies to protect that trade.

- [Narrator] Through the ages,

many port cities have prospered

and grown around
existing harbors.

- The preferred choice
for early sailors

was a natural harbor where
they would find an inlet

which was protected by land
from the sea, from the wind,

and therefore they could
set up their harbor

and then they could carry out
their trade all very safely.

- [Narrator] But not every
port city has a natural harbor.

Some had to be
created artificially.

[reverent music]

Caesarea, on the coast of Judea

in what is now
modern-day Israel.

At the end of the
1st century BC,

it was ruled by King
Herod of biblical fame,

an independent kingdom
under the ultimate control

of the Roman Empire.

To rival the architectural
marvels of Rome

and tap into its
lucrative maritime trade,

Herod embarked on
an ambitious plan

to found a new port city and
give it a grand manmade harbor.

- Herod's objective
here was to replicate

the success of
Alexandria in Egypt,

which was famed across
the Roman world.

So, he wanted to build a harbor

where he could export
good from Judea,

things like olive oil,

but also provide safe
harborage for Roman merchants,

which would then
enable all the wealth

from the Roman Empire
to come to Judea.

- [Narrator] But
this visionary idea

was never going to
be straightforward.

Judea lay on a particularly
long, flat stretch of coastline

in the Mediterranean
with no natural features

that could be used as a harbor.

- Virtually devoid
of bays and inlets.

If you wanted a harbor here,
you'd have to build one.

- [Narrator] But this coastline
came with another issue.

- It's also susceptible to
very strong longshore currents,

which causes shifting sands
and creates an unstable base,

very difficult for building
strong foundations.

- [Narrator] To help realize
Herod's maritime ambition,

his engineers looked
to one of Rome's

greatest engineering
innovations...

Concrete.

- It was strong, durable
and, crucially, easy to make,

and the Romans
used it everywhere.

So, they used it for
the amphitheaters,
for their theaters,

they used it in their aqueducts.

- [Narrator] But to build the
harbor foundations underwater

and to ensure it would withstand
the most turbulent seas,

the concrete needed to
be even more durable.

- Roman concrete famously
had many ingredients,

but one of the most famous
was pumice porcelain,

which is a volcanic ash which
comes from the Bay of Naples.

And this has a
very unique quality

because it enables Roman
concrete to set underwater.

- [Narrator] Herod imported
this crucial ingredient

all the way from the volcanic
basin of Vesuvius in Italy,

1,000 miles away.

- The Romans had very advanced
maritime transport networks,

which made it very easy to
transport the pumice porcelain

from Italy all the
way through to Judea.

- [Narrator] To create
the massive breakwaters,

the Romans floated
large wooden boxes,

called caissons, out to sea.

These were half-filled
with marine concrete

to stabilize them in rough seas.

From boats, the
caissons were then

fully filled with concrete
until they sank to the seabed.

This process was repeated

until the breakwater
foundations were complete.

Over time, the concrete
would slowly harden

and the wood would rot away.

This breakthrough allowed
them in just 10 years

to construct the largest harbor
ever built in the open sea.

- Herod called his new
harbor Caesarea Maritima

and it became one of
the most famous harbors

in the ancient world.

- [Narrator] Enclosed by
its two massive breakwaters,

it covered an area of 25 acres,

the equivalent of
20 football fields.

- The Roman engineers used

1.25 million cubic
feet of concrete

and all mixed without the
use of modern machines.

- Herod's ambition was big,

but his achievement
was incredible.

By the time it was finished,

the harbor was one of the
jewels of the Mediterranean.

- [Narrator] And it
stood the test of time.

Even 2,000 years later,

the harbor's concrete
breakwaters are still visible

due to a remarkable
chemical reaction.

- This reaction makes
a binder or glue

which bonds the volcanic
particles to the mortar

to make a very durable concrete.

- [Narrator] Volcanic
glass and crystals

inside the pumice dissolve

and react with alkaline
fluids in the concrete.

Over time, this
creates a mineral

called aluminous tobermorite,
which forms within voids

and prevents cracks from
traversing through the concrete,

increasing its resilience.

- The Romans used
their marine concrete

across their entire empire.

It was absolutely astonishing.

- [Narrator] But it's not
only defense against the sea

that ancient harbor-builders
have had to overcome.

[gentle music]

The Bosphorus, Istanbul.

Located in northwest Turkey,

it is the world's
narrowest strait

used for international
navigation

and one many have tried to
control throughout history.

[pensive music]

Back in the 8th century AD,

when the city was known
as Constantinople,

it was the center of
the Byzantine Empire.

- Founded by
Constantine the Great,

who was the first
Christian emperor.

Constantinople was built
in a key strategic location

because it's on the Bosphorus,

which links the Black Sea
with the Mediterranean.

- [Narrator] Due to its
geographical position,

Constantinople found itself

under constant
threat of invasion,

including, at this time
in the 8th century,

from the Arabic
Umayyads in Syria.

- Constantinople was famous
because of its walls.

It's a triple series of walls,

each one bigger than the other,

each one with a huge
ditch in front of it

and then a flat area of land,

which gives you
a killing ground.

So, it's almost impenetrable.

- [Narrator] While the
city's fortifications

protected it on land,

there was still one
major weak point:

the Golden Horn, a
great natural bay

that flowed through
the heart of the city,

leaving Constantinople
vulnerable to
attack from the sea.

- In the first few centuries
of Constantinople's history,

the Byzantine fleet was one
of its greatest strengths.

But during the 8th century,

there were a series
of naval defeats,

meaning that their navy
was severely weakened.

So, to protect their city,
they had to think again.

- [Narrator] Finding a way to
effectively defend themselves

would require a design
that drew on skills

acquired across a
range of disciplines.

- The Byzantines
were great engineers,

from siege weapons, grenades,
the pendentive dome.

- And they even invented
a mechanical throne

which allowed the
Byzantine emperor

to disappear below the floor.

- [Narrator] The solution came

in the shape of an
immense mechanical chain

at the entrance to
the Golden Horn,

a defense system
the likes of which

had never been seen before.

- And this involved an
enormous metal chain

which went all the way along
the entrance to the Golden Horn

and was set in place with
two towers at either side.

The real genius here
was that the chain

could be raised
or lowered at will

using very advanced
hydraulic technology.

- [Narrator] An
enormous cast-iron chain

almost half a mile in length

was strung between
two stone towers,

one on each side of the
entrance to the Golden Horn,

and held in place by eight
wooden floating pontoons.

To allow friendly
ships to pass over it,

the chain was lowered
between one set of pontoons

on each side of the river.

But when an invading
fleet approached,

the chain could be
pulled taut, raising it,

effectively closing any
safe passage through.

Despite its enormous
size and weight,

the chain could be maneuvered
surprisingly quickly

when an alert was given.

- Soon as the enemy is seen
coming over the horizon,

you can give the warning.

In as little as 20 seconds,
that chain could be raised.

- [Narrator] But its real genius
lay inside the two towers.

They contained a complex
hydraulic operating system.

Seawater from the Golden Horn
was channeled into the towers

and then pumped into
a holding tank above.

When enemy ships approached,

this water could
be quickly released

into large
counterweight containers

attached to each end of the
chain via a massive pulley.

[water sloshing]
As they filled with water,

the counterweights
lowered, raising the chain,

closing the gaps on each side
within a matter of moments

and preventing enemy invaders
from entering the Golden Horn.

- [Sam] Operating the chain
required exact coordination.

A lookout on each tower would
communicate with light signals

so they would know
the exact moment

to let water into
the counterweight to
operate the chain.

- And the reason why the chain

was so good at sealing
the harbor off was
the enormous size,

the enormous weight of
these cast-iron links

in the chain itself.

- [Narrator] With each link
weighing over half a ton,

this colossal chain defended
the city of Constantinople

from its enemies
on many occasions.

- The enemy ships trapped at
the entrance to the Golden Horn

could then be
attacked on two fronts

by military on the land and
also by Byzantine ships at sea,

perhaps using Greek fire,

a combustible compound
released with a flamethrower.

- [Narrator] When the
threat had passed,

water was released
from the counterweight

by unscrewing a
plug in the bottom,

forcing it to rise as
the weight decreased

and lowering the chain.

When the city finally
fell to the Ottomans,

it wasn't because of the
chains' ineffectiveness.

During the last siege
of Constantinople,

the chain, together with a
handful of Byzantine ships,

repelled the attempts of
Sultan Mehmed II's great navy,

forcing them to
find another route.

- When the Ottoman Turks
finally captured the city,

they had to drag their
warships over land

to get into the Golden Horn.

- [Narrator] The fall
of Constantinople

also marked the end
of the great chain.

Abandoned by the
victorious Ottomans,

it fell into obscurity
on the seabed.

Throughout history,

people have gravitated
to living near waterways.

And in ancient times,

entire cities were even
constructed on them.

- Venice is the most famous
medieval city built on water.

It was inhabited by people

who fled to the
swamps to survive,

and there they built the
most magnificent city,

all through the wealth
generated by maritime trade.

- [Narrator] Although people
have lived for centuries

in the Venice Lagoon, the city
is thought to have been built

from the 5th century AD onwards.

- Towards the end of the
Roman Empire in the west,

many Germans and Goths started
invading northern Italy

and the people living locally
needed a place of safety.

And so, they chose
a series of islands

surrounded by
lagoons and marshes,

which provide a natural
defense against the invaders.

- [Narrator] But building on
this soft, saturated marshland

wasn't easy.

- Given that this was just a
vast swamp with no firm ground,

it's an incredibly
challenging environment

to take on building
something of Venice's scale.

- This is the last
place on Earth

you'd dream of building a city.

Not only did they have to
build houses in the lagoon

but everything they used
to build those houses,

the raw materials,
had to come by sea.

- A key component in building
is the ground material.

There's a lotta sediment
brought in by sea

and a lot of soft sediment,
very difficult to build upon.

And of course, with
that tidal range,

you're facing designing
against flooding.

- [Narrator] The
engineers of Venice

needed an innovative way

to be able to support
their buildings

in such a waterlogged
environment.

- To create solid foundations,

the engineers had to drive
60-feet-long wooden poles

made of oak into the lagoon bed.

[reverent music]

- [Narrator] These
piles were driven into

the hard clay layer sitting
beneath the soft silt

and were tightly packed
together to keep them stable.

Voids between them
were filled with rubble

and capped by a platform
of wood and stone,

which extended
above the waterline.

Finally, a layer
of white limestone

was used as a damp course

to help stop the infusion of
water into the buildings above.

- If you could lift up Venice,

you would find a
forest of wooden piles,
10 million of them,

all supporting an entire city.

- [Narrator] This method of
building was so effective

that it changed little
over the centuries.

Today, the historical
center of Venice

has around 50,000 residents,

as well as millions
of tourists annually.

- Considering the foundations
of these buildings

is just in mud
and clay and sand,

it's incredible
that they've stayed

as stable and
secure as they are.

I mean, some have
subsided slightly,

but essentially the
city is still standing.

- [Narrator] And the fact
they have remained so solid

in the water is down
to clever engineering

and the unique environment
of the Venice Lagoon.

- The thing with the log piles

is that they have been preserved
because they're sitting in

what we call
anaerobic conditions.

They're underwater, they've
been starved of oxygen,

so they can survive for
hundreds, thousands of years

as long as they're kept wet.

- [Narrator] But
in recent decades,

the delicate balance of
Venice's original building work

has come under threat;
ironically, by modern engineers.

- In the 1950s and 1960s,

they were digging wells down
through the city's substructure

to get hold of fresh water
for their growing population.

The problem was
that once you start

sucking the moisture
out of the clay

within which the city is built

is it starts contracting
and you start getting voids

and the very posts upon which
the buildings are founded

start to sink.

- [Narrator] Together
with rising sea levels,

Venice faced
potential catastrophe.

[water sloshing]

[pensive music]

Venice's seasonal flooding,
known as acqua alta,

has increased in intensity
over the last few decades...

But modern engineers may
finally have found a solution:

the MOSE project,

a system of
electronically-operated
flood barriers

which can close off the
three main entrances

into the lagoon.

- What happens is when a
flood warning is given,

at a touch of a button,

the gates are initiated
and they rise up,

providing a barrier,

protecting the city to
flooding up to three meters.

- [Narrator] But while their
design is highly complex,

some simple engineering
underpins their operation.

78 giant steel gates

straddle the three entry
points from the sea.

When not in use, these
water-filled gates lie flat

within concrete bases
anchored to the seabed.

At times of
increased flood risk,

the water is expelled by being
replaced with compressed air,

causing them to rise, closing
off the lagoon from the sea.

For many years, the Venetians
doubted their effectiveness.

But in 2020, during an
exceptionally high tide

which normally would have put
half of Venice underwater,

the barriers were activated

and successfully
kept the city dry.

- Similar barriers could
be the saving grace

for various cities
across the world

with the rising sea levels
due to climate change.

- [Narrator] But Venice
is not the only city

which historically has had to
protect itself from flooding.

[reverent music]

Mesoamerica.

In the 14th century, in the
verdant valley of Mexico,

the Aztec people
were on a mission.

They were in search
of a promised land

where they would build
a great new city.

- Their tribal god,
Huitzilopochtli, told them,

"When you find an eagle
perched on a cactus,

"you would find the place

"where you are to
build a huge empire."

- [Narrator] Unfortunately
for the Aztecs,

the place they first
saw such a spectacle

was on a small marshy island
in the middle of Lake Mexico,

so that's exactly where
they built their city.

They called it Tenochtitlan,

likely meaning "place of
the prickly pear cactus."

- Tenochtitlan was a marvel
of the ancient world,

the beating heart of Aztec
power in what is now Mexico.

- It became so large

that it covered an extension
of five square miles,

which is really considerable

when we think that they
arrived in a marshy island.

- [Narrator] As the city grew,

the Aztecs expanded
their farming land

by building artificial garden
islands known as chinampas.

- Chinampas were key to the
success of Tenochtitlan.

Chinampas are
arable plots of land

that consist of earth from
the bottom of the lake

that is full of good nutrients,
full of organic components,

and it made for very
rich agricultural lands.

- [Narrator] As a result,

farming became
increasingly productive,

both in terms of
feeding the population

and in growing trade.

- The city grew in
size and importance,

and this was possible
thanks to the skill

of the engineers that were
working in Tenochtitlan.

- It was replete with
squares, temples,

storehouses, settlements,

and a network of paths and
canals to service all of that.

In many ways, this was
the Venice of Mesoamerica.

- [Narrator] However,
the Aztecs still had

a significant challenge
to contend with.

In the dry season,

Lake Mexico was one of
a series of six lakes.

[thunder cracking]

But in the rainy season,

these would join together,
creating one huge body of water,

not only flooding the city

but contaminating the
lagoon's freshwater

with the brackish
water of Lake Texcoco.

To overcome this, the Aztecs
built a vast flood defense

known as the
Nezahualcoyotl dike,

separating the lakes
once and for all.

It was an absolutely
enormous undertaking

on a scale never seen before:

a double wooden fence
roughly 10 miles long,

nearly 30 feet high,
and 12 feet wide.

- That enabled the people
there at Tenochtitlan

to grow crops and to create

this sort of
agricultural wonderland

that was absolutely central

to the success of
their settlement.

- [Narrator] Aztec engineers

chose the dry season
to build the dike,

when the water level was low.

A wooden barrier formed
from curved timber panels

was secured to the lake bed

by driving in huge wooden
piles at regular intervals.

Gaps in the barrier
were then filled

with a mix of dense
stone and clay

to help waterproof
the structure.

Wooden gates set into the dike

allowed the Aztecs to
regulate the water level

so when Lake Mexico
rose too high,

water could be released
into Lake Texcoco.

Through the Aztecs' mastery
of controlling water,

Tenochtitlan
eventually grew into

one of the largest cities
in the world at that time.

- Tenochtitlan
was built on water

and what really
is extraordinary,

how they were able to make
construction so solid.

These very
sophisticated buildings

were extraordinary
feats of engineering.

- It was from this base

that the Aztecs went on to
conquer much of Mesoamerica,

an empire that stretched from
the Atlantic to the Pacific.

- [Narrator] But everything
changed in the year 1521.

Spanish conquistadors
led by Hernan Cortes,

who had invaded Mexico
two years previously,

came across the city.

- So, when Cortes first
clapped eyes on this place,

he would have been taken aback

by this amazingly
sophisticated city.

I mean, here you had
all sorts of buildings,

you had tree-lined avenues,
a complex of waterways,

lush gardens, all
sitting on an island

in the middle of
this shimmering lake.

- [Narrator] What happened
next seems unthinkable today.

- The invaders destroyed it.

They destroyed this amazing
feat of engineering,

this incredibly
sophisticated city

at the heart of
this civilization,

and they destroyed the
Nezahualcoyotl dam as well.

I mean, this is in essence
wiping a civilization

off the face of the Earth.

It's an absolute tragedy

and it's something that I
think we'll regret forever.

- [Narrator] Today, the entire
valley basin has been drained

and is now occupied
by Mexico City,

leaving few traces of the lakes,

the city, or its great dike.

[gears turning]

Today, modern engineers
continue to challenge

the notion of what
can be built on water.

Palm Jumeirah: an archipelago
of artificial islands in Dubai

created through land reclamation

which extends into
the Persian Gulf.

First opened to
residents in 2007,

it's one of the world's most
unique residential projects

that, together with other
linked developments,

increases Dubai's shoreline
by a total of 320 miles.

To get the palm-shaped
design right,

engineers used a
cutting-edge technology

called differential
global positioning systems

to plot each island within
0.39 of an inch of accuracy.

- These unique artificial
islands were built

using 3.2 billion cubic feet
of sand dredged from the seabed

and brought all the way
from the Persian Gulf.

So, even though Dubai
is surrounded by sand,

it was the wrong type of sand.

It's too fine to be able
to build these islands.

- [Narrator] To ensure the
islands did not collapse,

state-of-the-art vibrocompactors

were used to help
solidify the sand.

Palm Jumeirah now houses
as many as 80,000 people.

And with its villas only
10 feet above sea level,

engineers also found a solution

to protect it from the tides,

constructing a massive
crescent-shaped breakwater.

[reverent music]

- It's one of the most
impressive manmade islands.

You can even see it from space.

- [Narrator] Such developments

in water-based
construction technology

may now be more the
preserve of the rich,

but some of these
engineering innovations

may become vital to the
future of entire populations.

- This is something
that will have to become

more common around the world

as climate change causes
water levels to rise

and we literally have
less land to live on.

- [Narrator] And
more extreme weather

may also mean our flood
defenses and waterways

will need to become
even more effective.

- With climate change
exacerbating extreme weather

and rising sea levels,

we're going to have to use new
innovations and old ones too,

whatever we can do to
protect our communities

from the adverse consequences
of a rising sea level.

- [Narrator] Modern engineers
may need to turn once again

to proven technologies
from the ancient world.

- I just hope that we
can take some inspiration

from the ways in which
ancient engineers

have fashioned watercourses,
dams and irrigation systems

and learn something
of that to inform

the way in which we sustainably
manage water in the future.

[reverent music]

- [Narrator] The
many innovative ways

in which ancient engineers
harnessed the power

and life-giving properties
of water became the catalyst

for the growth of all great
civilizations around the world.

From the Sumerians' and Aztecs'
complex irrigation systems

to China's
empire-unifying canal,

Herod's showstopping harbor
embedded in Roman concrete,

and the Venetians'
far-reaching vision

to construct an
entire city on water,

today's engineers
remain astounded

by the achievements of the past

and the potential of the future.

[reverent music continuing]