Original subtitles

male narrator: An industrial super factory

thousands of years ahead of its time...

- This really was the world's first mega factory.

narrator: A huge 2,000-year-old building

that grows stronger the older it gets...

- It's an enormous space.

You could hold over 5,000 people.

It's absolutely amazing.

narrator: A revolutionary machine

that transformed cities...

- If you can lift more, you can build bigger.

narrator: And the most ambitious

Roman engineering project of them all.

- Huge networks transporting gallons

upon gallons of water across the empire.

narrator: Where will they be ranked

in the only top ten list

thousands of years in the making?

[dramatic music]

♪ ♪

Rome engineered an empire

which stretched from the Atlantic to the Tigress.

At its peak, there might have been

up to 70 million citizens.

The Romans shaped our world

more than any other civilization

from antiquity.

This week's "Ancient Top Ten,"

Rome's Greatest Hits,

amazing Roman feats of engineering ranked

by experts according to which most changed the world.

♪ ♪

At number ten,

courtesy of Julius Caesar,

the bridge that beat the barbarians.

- Caesar's bridge over the Rhine

is incredible engineering

amazingly executed.

♪ ♪

narrator: In 55 B.C., Rome's greatest general,

Julius Caesar,

decided to launch an attack on the hostile Germanic tribes.

He wanted to expand and secure his empire

into what is now modern-day Germany,

but how was he going to get his whole army

of 40,000 men across the river?

Most leaders would simply go around it,

but Caesar wasn't going to let anything stand in his way.

- Caesar couldn't wait,

and he wasn't willing to accept that something couldn't be done.

And in typical Caesar fashion,

he was willing to try something bold and audacious.

narrator: Caesar's plan was an engineering breakthrough

and clearly demonstrated

the strength of Rome's power

to their enemies.

- This river had never previously been bridged.

This was a hugely ambitious project

at the very edge of the Roman world.

♪ ♪

narrator: Bridge building at that time

normally took months, if not years.

Julius Caesar did it in a matter of days.

- Caesar was trying to cross the Rhine at a point

where it was 1/4 of a mile wide.

So that's crossing a span

that's as long as the Empire State Building is tall.

narrator: The Rhine wasn't just wide.

It was 30 feet deep

with strong currents.

♪ ♪

These are military engineers in today's British Army.

They have modern, high-powered,

mobile bridge-building equipment.

♪ ♪

But Julius Caesar had to start from scratch.

- 40,000 Roman troops start chopping down

all the trees in the area.

They didn't just need timber for the bridge itself.

They also needed timber to create a huge floating crane

and an enormous pile driver.

narrator: The pile driver would hammer in giant wooden stakes,

which would give the bridge stability

and allow it hold the weight of Caesar's massive army.

This wasn't a standard method of construction.

It was revolutionary engineering,

and the Romans were inventing it on the spot.

With the piles in, the bridge advanced the length

of three school busses every day.

That's faster than modern engineers can do.

- The Germanic tribes were on the other side of the river

thinking they were safe,

and you can just imagine their horror

when this bridge started to creep towards to them.

narrator: The bridge took just ten days.

It was long enough and strong enough

to hold the entire army.

- It was a real incarnation

of the might that was Rome.

- Caesar was the master of the publicity stunt.

He marched across this bridge

and said, "Here I am.

I can do whatever I want."

Then he marched back and tore it down.

narrator: The bridge was destroyed,

but the point had been made.

- It cemented Rome's reputation as a military might

more than any bloody battle would have done.

♪ ♪

narrator: And the bridge was an early example

of using piles for support.

♪ ♪

Today, steel and concrete piles

are the norm for making things stable.

Caesar and his engineers

were thousands of years ahead of their time.

♪ ♪

Like Caesar's bridge,

the next Roman marvel on our countdown

was also the product of the mighty Roman military.

♪ ♪

Shooting in at number nine,

the repeating ballista,

also known as the polybolos.

- It's a Gatling gun.

The same idea as today, but 2,000 years ago.

narrator: The Roman army couldn't be matched.

Organization, tactics, weaponry.

Their weapon of choice was the ballista,

a giant wooden crossbow

that could launch bolts a quarter of a mile.

But they were always looking to improve

and to make their weapons even more deadly.

♪ ♪

The Romans inherited a new design from the Greeks,

and took it to another level. A repeater.

This was the machine gun of its day.

- The repeating ballista could fire one bolt

about every ten seconds,

which doesn't sound like that much until you realize

that it actually tripled the rate of fire

that the Romans had previously had.

♪ ♪

This was a devastating weapon.

- It was a barrage. It was a deadly rain of bolts,

and we're talking 1,500 years

before the first artillery barrage.

♪ ♪

narrator: A repeating weapon was sophisticated

ancient engineering.

It had a gravity-fed magazine,

which would be constantly dropping bolts down one by one.

Winding the mechanism pulls back the string,

and the ballista fires automatically.

As long as the magazine was kept loaded,

this ancient machine gun could fire continuously.

It's known as a chain drive,

and it was the first in Western technology.

- The Roman engineers were the first people

to master the chain drive.

They were so ingenious.

narrator: Years ahead of its time,

this technology wouldn't be seen again

until the 16th century when Leonardo da Vinci

supposedly reinvented it.

The engineering genius behind the polybolos

was centuries ahead of its time.

- Amazingly, there's nothing as effective on the battlefield

for over 1,000 years.

narrator: It was the pinnacle of Roman military engineering,

and the principles behind the polybolos underpin

our modern mechanics today.

♪ ♪

The development of technology

has seen our cities advance at a staggering pace,

but our survival still depends on the one basic need

that hasn't changed in millennia,

water.

Coming in at number eight,

it's the Basilica Cistern of Constantinople,

modern day Istanbul.

A giant underground reservoir

providing a clean, safe water supply.

- Underneath modern-day Istanbul there's a subterranean treasure.

It's the Basilica Cistern.

It was actually dug out by 7,000 slaves

working in appalling conditions

so it's a wonder of the medieval world,

but it has a very dark history.

♪ ♪

narrator: The Basilica Cistern

was built was not only to be a source of water,

but to form part of the city's defenses.

♪ ♪

The cities of the Empire

were a prime target for invasion.

They would be taken by force,

and the best way to do that was with siege warfare.

- As long as we've had cities and fortresses,

we've had siege warfare.

The defenders have to wait it out.

The attackers have to find a way to starve them,

thirst them, or just make them give up.

These things can take years, and if you think about it,

it really is just a tactical chess game,

and who's gonna win?

It might take forever to find out.

♪ ♪

narrator: In ancient times,

for a city to be secure

and to withstand a siege,

it took more than strong walls and an army.

What was needed most was a safe supply of water.

- If there's no water inside the city,

then you can be held to ransom.

narrator: And having it underground

meant it was protected.

- As soon as you can secure a water source inside the city,

in a cistern, for example,

you have got the upper hand.

narrator: And that's exactly what the Romans did

at Constantinople.

But this city's incredible piece of engineering

lay hidden beneath the streets,

a secret for hundreds of years.

How was it discovered?

It's coming up next on "Ancient Top 10."

♪ ♪

narrator: This is Rome's Greatest Hits,

amazing Roman feats of engineering ranked

by experts according to which most changed the world.

♪ ♪

The city of Istanbul in modern-day Turkey.

In Roman times it was called Constantinople

and was capital of the Eastern Roman Empire.

♪ ♪

Its buildings concealed a secret

that laid undiscovered for thousands of years,

something so important it had to be hidden deep underground.

♪ ♪

Number eight in our countdown.

♪ ♪

- 500 years ago in Istanbul

there were people in residential neighborhoods

who were able to open up the floorboards

and the stones of their houses,

lower cups and jugs down,

and bring up water for drinking

and washing their clothes.

♪ ♪

They launch an expedition, they dug down deep,

and they found the Basilica Cisterns.

♪ ♪

narrator: The Basilica Cistern,

deep underground,

but today open for the public to view.

Over 400 feet long and 200 feet wide,

the biggest and most magnificent cistern

in antiquity.

It's as big as an underground cathedral.

narrator: It's believed the Romans

transferred this sculpture

from another temple

in order to keep construction costs down.

- The Romans were nothing if not practical.

narrator: The Basilica Cistern wasn't the only

sophisticated water system in ancient times.

♪ ♪

In 73 AD, there was an uprising of Jews

against the Romans.

Despite being surrounded and their supplies cut off,

a rebel force was able to hold out for months

in the mountain fortress of Masada,

in what is modern-day Israel,

thanks to a cistern providing

a ready supply of fresh water.

And Alexandria in ancient Egypt

had a remarkable cistern under the city,

making it a major stronghold.

But the water supply delivered to Constantinople

by the Basilica Cistern was unmatched.

It was the largest and most impressive

in the ancient world.

♪ ♪

- The Basilica Cistern was huge.

It stored 22 million gallons of water,

so that gave Constantinople its strength and its security.

It meant the city could not just survive,

but thrive.

narrator: This engineering marvel

would not be bettered for 1,500 years.

The Romans used advanced technology and engineering

to ensure that the cistern was built to last.

- The walls of the Basilica Cistern are 12 feet thick

and they're lined with waterproof cement,

and it still works.

It's not a ruin. It still functions.

It still holds water.

narrator: Thanks in part to

this incredible piece of Roman engineering,

Constantinople was able to

withstand repeated sieges

for nearly 1,000 years to overtake Rome

and become the greatest city in the world at the time.

♪ ♪

Control of water was also behind

the next engineering great.

At number seven...

♪ ♪

The Nemi Tunnel.

♪ ♪

19 miles south of Rome is a sacred lake,

Lake Nemi.

♪ ♪

In the early Roman period,

the lake was prone to flooding.

At the lakeside was a temple to the goddess Diana,

and allowing her temple to flood was simply unacceptable.

The Romans came up with an extraordinary solution,

to build a tunnel through a mountain.

- The Nemi Tunnel was over

a mile long through a solid mountain.

This is ancient engineering at its most sublime.

♪ ♪

narrator: The tunnel was built around 500 BC.

♪ ♪

Constructing any kind of tunnel back then

was an extraordinary feat,

let alone one this long.

♪ ♪

And 2,500 years later, it's still intact.

- The Nemi Tunnels were actually dug out by hand.

This was harsh, horrendous manual labor,

but they persevered to the end

and dug out a staggering 5,000 feet.

narrator: The Roman workers only had simple tools

and just the light of small oil lamps.

In the tunnel it was dark, cold, and wet,

but this tunnel was built with such accuracy,

even modern engineers would struggle to match it.

Today, we use lasers to tunnel in a straight line.

Unbelievably, the Romans started digging from both sides

of the mountain at once,

and, somehow, met partway through.

- It's absolutely incredible.

How could they build this without modern building

and surveying equipment?

narrator: Two tunneling teams worked independently

with incredible precision.

♪ ♪

When they met, the paths they dug

were within ten feet of each other.

- Both sides meeting with pretty impressive accuracy,

and it travels across an impossibly gentle gradient.

♪ ♪

- The tunnel's over a mile long,

and in that entire distance,

it drops by just 41 feet.

That's an average gradient drop of less than 1%.

narrator: Even today, we don't know exactly how they did it.

It could be an example of skills and technology

that have been lost to time.

This workmanship has kept the tunnel in use

right up to recent times.

♪ ♪

In the 1930s,

the Italian dictator Mussolini

used it to drain Lake Nemi.

He wanted to recover what lay at the bottom,

the priceless remains of two ships

built for the Roman emperor Caligula.

The lake gave up its secrets,

but the tunnel's impressive construction

still remains a mystery.

♪ ♪

Our next invention uncovers the dark side of the Romans,

and it only came to light after the discovery

of a mysterious ancient wheel,

the likes of which have never been seen before.

It led historians to a Roman underground hell

that would claim the lives of countless slaves.

♪ ♪

narrator: This is "Ancient Top Ten's"

countdown of the most amazing feats of Roman engineering,

shining a light on technology that would change the world.

Rolling in at number six...

[dramatic music]

Is the underground hell

of the silver mine at Rio Tinto.

♪ ♪

The Roman Empire spread all the way from Britain

to the Middle East,

but it was here, in the hills of southern Spain,

that 100 years ago,

the remains of this strange wooden wheel were found.

What could it be?

It was soon discovered to be Roman,

and it was over 2,000 years old.

- What the experts soon realized was that

they discovered a giant water wheel

14 1/2 feet in diameter.

And the most amazing thing, it hadn't been buried.

It was supposed to be underground.

narrator: This water wheel was part of the machinery

of an ancient silver mine

known as Rio Tinto.

Precious metals like silver and gold

were crucial for the Romans.

Their huge empire needed paying for.

Massive building projects, the military,

and their administration.

Somehow, this all needed to be funded.

- The 60 million citizens of the Roman Empire

needed a currency to trade in.

To get that currency, they needed pure silver.

narrator: In order to get this silver,

they constructed underground mines,

but they had a problem.

The mines were prone to flooding

from subsurface water supplies,

so the Romans constructed huge water wheels.

They were used to drain the water away from the mine.

How was this done?

Buy the feet of slaves.

- Huge underground water wheels being walked on by slaves.

It's crazy, isn't it?

Would you have liked to be the Roman engineer

who floated that idea?

They must have thought he was nuts.

narrator: Incredibly, there were eight pairs

of wheels raising the water from one cavern to the next

and up out of the mine.

Once again, the Romans were using

their engineering genius to overcome nature.

- The whole system could lift water

the height of a ten-story building.

narrator: These astonishing wheels never stopped.

They were worked 24 hours a day.

- It's estimated that one slave could raise

21 gallons of water per minute,

so that means the whole system could lift 180,000 gallons

of water every day.

narrator: Most of these slaves didn't live much over a year,

and when they died, the Romans didn't even bother

taking their bodies to the surface.

- This worked out fantastic for the Romans,

but not so well for the slaves.

It's impossible to imagine the horrifying lives

that the slaves endured down in the mines.

narrator: Sacrificing lives

for an incredible feat of engineering.

This was typical of the Romans.

Without mining the riches of Rio Tinto,

the empire would never have been able to expand so far.

♪ ♪

A growing empire brought with it

a growing population.

They all needed to be fed,

so the Romans used technology

to do it on a massive scale.

Next in our countdown is an extraordinary food factory.

It could be described as Roman fast food.

Coming in at number five...

♪ ♪

The amazing water mills of Barbegal.

♪ ♪

This is Barbegal in southern France,

near the city of Arles.

♪ ♪

In the 1940s, experts realized

that these strange ruins were the remains

of something truly spectacular...

♪ ♪

A series of water mills producing huge amounts

of flour thousands of years

before the industrial revolution.

To this day, there has never been anything else like it.

- It's an industrial super factory, and it's Roman.

narrator: Water mills were already used

in food production individually.

The ancient Chinese had them and the Greeks too.

But mills linked together was something completely new.

It was a huge technological leap.

- They didn't just have one water wheel, they had 16.

This really was the world's first mega factory.

- The water flowed through a series of mills

powering each one in turn.

Now, that's only a drop of 65 feet,

but each water mill is going to be receiving

33 gallons of water every second.

That's a huge energy output.

narrator: Unlike most conventional water wheels

which were powered by the flow of a river

at the bottom of the wheel,

these were overshot water wheels,

the difference being that they were powered by the water

dropping on the wheel from above,

a much more powerful method.

The construction of this new system

was a huge technical challenge.

- To power these water wheels,

the Romans actually diverted a nearby aqueduct.

♪ ♪

And even more impressively,

they cut a channel through the solid rock

of a mountainside to create a passage

for the water to reach the wheels.

♪ ♪

- Enough flour was made there

to produce 9,000 loaves of bread every single day.

narrator: That's 4 1/2 tons of bread daily.

This was enough to feed the Roman troops nearby

as well as the recently conquered Gauls in Arles.

If their new citizens were fed and watered,

the Romans knew they would be less likely to rebel.

As well as grinding flour,

the mills could be used for other purposes too,

such as powering mechanical saws.

Barbegal might well have been the world's

first multipurpose factory.

It's been described as the greatest

know concentration of mechanical power

in the ancient world.

This was an industrial revolution 2,000 years ago.

narrator: This is "Ancient Top Ten's"

Rome's Greatest Hits, Roman engineering breakthroughs

ranked according to their effect on the world.

Number ten was Caesar's amazing bridge across the Rhine.

At number nine, the incredible repeating ballista.

Number eight was the magnificent Basilica Cisterns.

And number seven, the intriguing Nemi Tunnels.

Six was the horror that was the mine at Rio Tinto.

And number five,

astonishing ancient industry at Barbegal.

But next in our countdown is an engineering breakthrough

that was bigger still.

It transformed the face of the towns

and cities of the Western world.

At number four...

[dramatic music]

Elevating the Romans to new heights,

it's the ingenious crane, the polyspastos.

Building in the ancient world was hugely labor-intensive.

Every massive block of the mighty Egyptian pyramids

was hauled up by manpower alone.

But Roman engineering was to change building forever.

They invented the ultimate lifting machine.

- The polyspastos was a massive breakthrough.

It allowed the Romans to build bigger and faster

than they'd ever done before.

narrator: This revolutionary machine

was many pulleys joined together into a crane,

hence the name polyspastos,

meaning multiple pulleys.

The amount that one crane could lift increased massively

to over 3 tons.

- This crane allowed each person

using it to shift 60 times

as much as they would otherwise.

Roman engineering went into overdrive.

♪ ♪

- Incredible buildings and monuments,

how are they made possible?

With this amazing crane.

♪ ♪

The polyspastos crane built Rome.

- But the Roman engineers didn't stop there.

They took things one step further.

♪ ♪

narrator: The crane's original design

used a capstan to lift the arm,

which is a horizontal wheel turned by hand.

But again, the Romans saw the opportunity

to make their invention more powerful.

- They swapped out the capstan for a treadwheel,

which was walked by slaves,

thereby doubling the lifting capacity of the crane.

If you can lift more, you can build bigger.

♪ ♪

- It may be even possible that several polyspastos cranes

were used together in one big interlocked mechanism.

And if that's the case, imagine the lifting power.

The sky is the limit.

♪ ♪

- They basically liked to show off.

Not only did they want to prove

that they had mastery over the natural world,

they also wanted to intimidate their enemies.

♪ ♪

narrator: Nothing changed the face of the empire

as much as this remarkable crane.

And the monster lifting machines of today

and the skylines that they've built

have all evolved from this groundbreaking device.

♪ ♪

Our next Roman breakthrough was a monumental

engineering project at ground level.

At number three...

♪ ♪

The extraordinary and revolutionary system

of Roman roads.

♪ ♪

Before the Romans, people used simple tracks,

but the Romans wanted to march their armies

across their empire,

not to be constrained by their environment.

They knew a well-built and reliable system of roads

would be good for trade, and for their military.

Road building went into overdrive.

- There are over 250,000 miles

of known Roman roads.

There are probably actually even more

that we simply don't know about.

That is more

than the distance to the moon.

♪ ♪

narrator: No civilization since

has ever built on such a scale.

372 great roads connected

the empire's 113 provinces.

- In those days, the saying "all roads lead to Rome"

was more than just a saying.

It was the literal truth.

narrator: On a newly constructed road,

a Roman legion could march about 20 miles a day.

The mile itself is a Roman invention.

It was created to measure 1,000 steps of the army.

narrator: The Romans created their roads with precision

and incredibly modern techniques.

- The most amazing thing about Roman roads

is their construction.

That's what makes them such incredible feats of engineering.

narrator: And they were built to last.

- There were large stones at the bottom,

laid up with smaller stones

and then gravel hard packed on top.

narrator: They're famous for being straight

because it's the most efficient way

to reach your destination.

But straight roads were also a sign of Roman power.

They built them straight because they could,

whatever the obstacles,

and much of the huge network

can still be seen to this day.

- The ingenuity of their design,

and the sheer amount of mileage

that they covered, means that the Roman road system

has to have its place in any Roman top ten.

narrator: Roads were the glue

that held the Roman Empire together,

and they still connect towns and cities today.

♪ ♪

The Romans used a secret ingredient

in their road construction,

something that transformed engineering and architecture.

It's a 2,000-year-old technology

that most would think was only invented

in the past few hundred years.

Today we take it for granted.

It's all around us

and this extraordinary revolutionary breakthrough

is coming up next as our number two

on "Ancient Top Ten."

♪ ♪

narrator: Roman construction that changed the world.

This is Rome's Greatest Hits,

the most incredible feats of Roman engineering.

[dramatic music]

Next on our list is

an engineering breakthrough

that revolutionized construction

in the ancient world,

and thousands of years later,

our modern engineering depends on it.

At number two...

♪ ♪

Is concrete.

- Concrete.

The Romans invented concrete

2,000 years ago.

We think of concrete as a modern discovery.

But in fact, it's reinvention.

It's rediscovery.

narrator: The Pantheon in the middle of Rome,

one of the most astonishing buildings ever built.

It's 2,000 years old and still intact,

and its huge dome

made entirely of unreinforced concrete.

♪ ♪

- The Pantheon was built as a temple to honor

all of the Roman gods.

It actually has the largest unreinforced

concrete dome in the world.

The fact that this is still standing today

just stands as a testament to the awesome engineering minds

of the ancient Romans.

narrator: The beauty of concrete

is that it can be poured

and molded into blocks of any shape.

The Romans could make arches,

vaults, and domes.

This was an architectural revolution,

and the Pantheon is the pinnacle

of Roman concrete construction.

- The dome of the Pantheon is a fantastic example

of how good the Romans were

at building in concrete.

It's 142 feet in diameter

with no columns to support the dome.

That is 50% bigger than the dome

of the Capitol Building in Washington.

♪ ♪

- The diameter of the Pantheon is the same

is the height of the structure.

It's an absolutely enormous space.

You could hold over 5,000 people inside the Pantheon.

It's absolutely amazing.

♪ ♪

- Roman concrete technology was incredible.

In fact, they varied the densities

of the aggregate in the cement.

They would use high-density aggregate

in the foundations and in the walls,

but then, up in the dome

where the cement had to be a lot lighter,

they would use a lower-density aggregate.

narrator: It's this ingenious engineering

that allowed the Romans to build in concrete

without the need for reinforcement or pillars.

- There's one very special quality of Roman concrete.

It continues to harden with age.

The dome of the Pantheon is now stronger

than it was 2,000 years ago.

narrator: Modern concrete buildings rarely last 50 years.

They are in constant need of repair.

♪ ♪

The Capitol dome was finished in 1856

and has had two extensive restorations since then.

The last time the Pantheon dome

was repaired was 202 AD,

and that was after an earthquake.

And there was another astonishing feature

of Roman concrete.

- Roman engineers were so ahead

of their time that they discovered that

if they changed the chemical composition of concrete,

this would allow the concrete to set even under water.

narrator: Underwater concrete, this was revolutionary.

The key ingredient,

a volcanic ash from the slopes of Mt. Vesuvius.

- It contained about 85% volcanic ash,

lime, water,

and some even say animal's blood.

This stuff was strong.

narrator: It doesn't let water in like modern concrete.

It's weather-proof, and resistant to decay,

and incredibly, it meant that the Romans

could build in the sea and construct harbors.

- They could build artificial harbors

wherever they wanted.

The Roman Empire flourished.

narrator: The Romans poured the concrete into wooden crates,

which then sank into place,

and the concrete set on the sea bed.

They did this again and again,

building up the harbor,

the concrete continuing to harden over time underwater.

♪ ♪

The biggest concrete harbor the Romans built

was at Caesarea in modern-day Israel.

♪ ♪

They shipped in 44 ships,

each containing 400 tons of volcanic ash.

♪ ♪

With concrete, they built one of the biggest harbors

in the ancient world.

narrator: Caesarea harbor was 90,000 square yards.

That's big enough to enclose 30 football fields.

It could accommodate 300 ships.

- They used over a million cubic feet of concrete

to build it,

and this thing extended out into the sea almost half a mile.

It was massive.

♪ ♪

narrator: Concrete was an engineering breakthrough,

and it has literally shaped our world

more than any other ancient invention so far.

♪ ♪

We've seen the most incredible structures and discoveries,

but there can only be one number one,

the greatest feat of Roman engineering of all.

Quite simply, it was the biggest construction project

the Roman Empire ever undertook

and it was unsurpassed,

not for hundreds of years, but for millennia.

The greatest Roman engineering breakthrough

is next on "Ancient Top Ten."

♪ ♪

narrator: It's Rome's Greatest Hits,

"Ancient Top Ten's" list

of the most amazing feats of Roman engineering.

[dramatic music]

At number ten,

we saw Caesar's incredible bridge,

and number nine was the deadly repeating ballista.

♪ ♪

At number eight, the underground cathedral,

the Basilica Cistern,

and number seven, the extraordinary Nemi Tunnel.

Number six was the horrific mine that was Rio Tinto.

And then at number five, Barbegal,

ancient industry.

Number four was the mighty polyspastos crane.

Number three, the amazing road system,

and number two, the concrete revolution.

But what has been picked as the greatest

engineering feat of them all?

What changed the world more than anything else?

It's the number one Rome's Greatest Hit...

♪ ♪

Aqueducts.

- Aqueducts were the arteries of the Roman Empire,

and the Romans were master engineers

at building them.

narrator: Rome built its first aqueduct in 312 BC.

It was such a success that they went on

to build them far and wide.

- A marvel of Roman engineering.

Huge networks

transporting gallons upon gallons

upon gallons of water across the empire.

narrator: It's estimated that the Romans

built 6,000 miles of aqueducts,

which if laid end to end,

would go 1/4 of the way around the world.

♪ ♪

A ready supply of fresh water

meant that Roman civilization could flourish.

Agriculture, industry, and expansion of the empire.

- They could establish cities in places

that they otherwise couldn't

because they wouldn't have had a secure supply of drinking water.

narrator: All across the empire,

a supply of fresh water

meant that cities could grow and prosper.

♪ ♪

The main aqueduct supplying the city of Rome

was an incredible 57 miles long,

but this wasn't the only one.

- Eleven aqueducts totaling more than 300 miles in length.

That's 183 Golden Gate Bridges.

♪ ♪

- In total, over 300 million gallons

of water flowed into Rome each day.

That's more per person than modern day New York City.

narrator: Enough for drinking water, sanitation,

bath houses,

and even the occasional spectacular event

on an epic scale.

- One of the most remarkable engineering feats

associated with the Colosseum is for the inaugural games,

they actually flooded the arena floor

for naval battles,

and the next day had it all drained out,

and the stage back in place.

narrator: Just as amazing is the precision engineering

that went into Roman aqueducts,

and none more so than the Pont du Gard

in Southern France.

- This thing is huge.

16 stories high.

164 feet.

It's the height of the Colosseum.

Enormous.

It's made of over 50,000 tons of stone,

and it's still standing.

♪ ♪

- The bridge over the gorge covers

just a small section.

The whole aqueduct actually travels for 30 miles.

Even today, that would be a public works undertaking

on an unimaginable scale.

♪ ♪

narrator: The precision engineering

that went into Roman aqueducts

like Pont du Gard is incredible.

- The wow fact that stays in my mind

is that over the course of the whole aqueduct,

that's 30 miles,

the drop in height is only 55 feet.

That is an absolute tour de force of Roman engineering.

narrator: The gradient is less than 1%,

imperceptible to the naked eye.

- With a one-foot drop every 3,000 feet,

the rate of flow was 58 gallons per second.

That's pretty amazing.

narrator: And there was yet another

technological innovation that was

way ahead of its time, the inverted siphon.

As long as one side is slightly lower,

water flows from one pipe down,

then up to the other.

It meant that no valley was too wide to cross.

- The inverted siphon, ingenious.

Not only could water be transported

along level ground and downhill,

but thanks to this innovation,

they could transport water uphill.

narrator: When this principle was applied to huge aqueducts,

the Romans could transport water no matter the terrain.

There could even be a series of these tanks

from one valley to the next.

- The Romans perfected the inverted siphon technique,

and they rolled it out across the entire Empire.

In any one hour, they could

make 10 million gallons of water flow.

Not just flow, it flowed uphill.

narrator: An infrastructure project on this scale

had never been tried before.

It hadn't even been contemplated.

- But that's what the Romans were like.

They'd come up with the most amazing solutions

no matter how crazy or ambitious the plan.

♪ ♪

narrator: Aqueducts were the veins of the Roman Empire.

Their civilization depended on them.

The world hasn't seen engineering on this scale since.

♪ ♪

Roman engineering was the greatest

of the ancient world.

It overcame any obstacle in its way

centuries ahead of its time.

It transformed the Roman world,

and in doing so, it has transformed ours too.