Original subtitles

NARRATOR: How did the ancients build a beacon taller

than the tallest lighthouse in America today?

Were the ancient Egyptians capable of creating a giant

circular saw that could cut through solid granite?

How did Julius Caesar build a bridge across the mighty Rhine

River in just 10 days and then march his army of over 40,000

across it?

And the secrets of the greatest harbor of the ancient world,

Rome's Portus.

[frenzied music playing]

[rocks falling]

Monument's more colossal than our own,

agent superweapons as mighty as today's, technology so precise,

it defies reinvention.

The ancient world was not primitive.

Their marvels are so advanced, we still use them now.

Travel to a world closer than we imagine, an ancient age

where nothing was impossible.

[frenzied music playing]

[suspenseful music playing]

In the modern world, iconic, man-made structures

reach out across the oceans, welcoming beacons of progress.

The Statue of Liberty, 300 feet tall,

dominates New York Harbor.

But is it possible that this engineering marvel

would have been dwarfed by a construction created

by ancient engineers over 2,000 years ago?

And what of this, the Cape Hatteras Lighthouse in North

Carolina?

It's the tallest in the United States.

Could there have been an ancient lighthouse twice as high?

The answer to both these questions

lies in one incredible structure.

It's a building that's shrouded in legend and rumor.

But not only did it exist, it stood for over 1,500 years.

It was the Pharos, the great lighthouse of Alexandria.

DICK STRAWBRIDGE: The lighthouse of Alexandria

was the daddy of all lighthouses.

It was one of the tallest man-made structures on Earth

for centuries.

And even compared to modern lighthouses,

it stood head and shoulders above them.

This lighthouse is 85 feet tall.

That's pretty big.

The lighthouse of Alexandria, around 400 feet high.

That's impossibly big.

The Pharos lighthouse was one of the seven wonders

of the world and deserved to be.

It was one of the tallest and most massive buildings.

And it was built to a very, very high standard indeed.

There's never been anything like the Pharos lighthouse before.

DICK STRAWBRIDGE: The structure of the lighthouse of Alexandria

was incredible.

It had a huge, square base.

It was made of granite blocks that were sealed together

with molten lead to protect it from the waves.

Next came an octagonal tier.

On the top of that, a cylindrical tier.

It would have dwarfed this.

NARRATOR: It was the equivalent of a 40-story building.

Julius Caesar called it a work of wonderful construction.

Modern lighthouses like this one in Happisburgh, England,

are by comparison, small, temporary structures.

DICK STRAWBRIDGE: This lighthouse

stood for like two centuries.

That's better than some.

But the Pharos lighthouse, it was built around 280 BC

and was still standing in the 1300s, over 1,500 years.

That's unbelievable.

NARRATOR: It was the first, the biggest, and the best.

It set the benchmark.

And when the Romans came across it,

they saw how useful lighthouses could be,

and built them throughout their empire.

The remains of one can still be seen in Dover, England.

Dover was the key harbor into Britain.

A lighthouse here was incredibly important.

MARY-ANN OCHOTA: This one looks impressive.

The one in Alexandria absolutely blows it out of the water.

It's almost impossible to believe that they could marshal

that kind of architectural and engineering expertise,

but they did.

DICK STRAWBRIDGE: Did the lighthouse of Alexandria

really need to be so tall?

Well, it was built for the Kings of Egypt.

And they wanted to make a grand statement.

PROF.

ALAN LLOYD: This was built by the dynasty of kings

who succeeded Alexander the Great in Egypt.

They regarded Alexandria as a great theater

for projecting their power and magnificence and grandeur.

Everything had to be bigger and better than it was anywhere

else.

A bit like New York, really.

MARY-ANN OCHOTA: It was so impressive,

that people from around the known world

traveled to see this miracle wonder of a building.

They used to stamp pictures of it on coins.

They used to sell models of it.

And when visitors arrived, they could buy that ticket.

It was basically the Empire State Building of its day.

It was that famous.

PROF.

ALAN LLOYD: There's talk of an observation platform.

And I wouldn't be at all surprised if there were people

up there selling the ancient equivalent of hamburgers

and little models of the lighthouse

that they could take back to their homes.

[whooshing sound]

NARRATOR: At Dover, the Romans were less interested

in tourism.

They had an empire to build and wanted

to make sure their ships had safe passage.

MARY-ANN OCHOTA: This lighthouse didn't stand alone.

It was actually part of a pair, with another tower over there

on the Western heights.

And they stood either side of the natural harbor in Dover.

[electronic sounds]

NARRATOR: And with a similar setup across the channel

in France, Roman sailors could safely

navigate between the two.

MARY-ANN OCHOTA: By using the towers together,

seamen could effectively use an ancient form of GPS

to know exactly where they were, and how

to travel safely, and find safe passage to the harbors.

It was pretty clever.

NARRATOR: At night the Roman, houses burnt dry wood

to create the brightest fire.

In the daytime, they probably burnt wet wood, which

would create a smoke signal.

The most incredible thing about the Pharos lighthouse

is the accounts of something unbelievably high tech in use

at the top, with remarkable similarities

to a modern lighthouse.

This is the important part of a lighthouse.

Originally, there would have been candle lanterns in here.

But like all modern lighthouses, we've got electricity

and we've got prisms to focus the light.

This light from the lighthouse can

be seen 18 miles out to sea.

The Pharos lighthouse could be seen 30 miles out to sea.

It makes you wonder what was generating that light.

PROF.

ALAN LLOYD: During the day, a distinct possibility

would be the use of large mirrors, which might well have

been rotated to give a flashing effect,

like the sort of thing you get in modern lighthouses.

NARRATOR: A flashing lighthouse, just like today's, over 2,000

years ago.

This sounds impossible.

But model maker Richard Windley has recreated

how it might have worked.

My theory, and it is a new theory,

is that a mirror would collect the sun's rays from somewhere

in this direction into this top mirror, which

had to be precisely angled so that the beam went absolutely

vertically down below.

The beam would be reflected down below to the mirror

here, which then could be rotated to distribute

the light a bit in the same way as a modern lighthouse would

do.

NARRATOR: A great mystery has arisen behind the use

of mirrors and the Pharos.

Could there have been more to them than just providing

safe passage?

PROF.

ALAN LLOYD: We are told that the mirrors could

be used to concentrate the rays of the sun to destroy ships.

NARRATOR: An incredible ancient weapon,

like something from the space age.

Could it have been true?

[thrilling music playing]

Alexandria was home to the greatest library

of the ancient world.

And the city wanted it protected.

But even if there was no superweapon, just

the rumor of one, would have been

enough to make anyone think twice

before attacking Alexandria.

PROF.

ALAN LLOYD: It wouldn't do any harm,

would it, if the word got out that they

had a kind of super ray gun on top of the Pharos lighthouse

that could destroy ships.

Very much don't tread on me or else.

NARRATOR: The lighthouse was certainly

in a good, defensive position.

That's why today, this 15th century fortress

marks the location.

With or without the ancient superweapon,

the Pharos of Alexandria was one of the most extreme examples

of ancient engineering.

The lighthouse at Alexandra was truly

a wonder of the ancient world, the size

of a modern skyscraper.

Even today, it would be thought of as an amazing feat.

It's never been bettered.

[thrilling music playing]

NARRATOR: The Pharos was built so well that it took

multiple earthquakes to eventually bring it down

in the 14th century.

It was a dramatic end to an incredible construction.

[thrilling music playing]

Many of the most incredible engineering projects

of the ancient world happened in Egypt thousands of years ago.

They built amazing structures, incredible temples and tombs,

the Great Sphinx, and the pyramids of Giza.

[electronic sounds]

But now, there's evidence of more impossible engineering.

This mysterious stone slab was found

at Abu Rawash, site of the unfinished pyramid,

five miles from Giza.

It was discovered near an ancient boat pit in which

a boat would have been buried to transport

a dead king to the afterlife.

Remarkably, the slab seems to suggest

that the ancient Egyptians were using engineering techniques

thought unknown until the 19th century,

4 and 1/2 thousand years later--

surely impossible.

The slab is made of granite, which is one of the hardest

rocks.

We know that the Egyptians used copper tools.

But copper is softer than granite.

And they managed to cut the granite so finely.

How did they do it?

DR. DEREK MULLER: I find this line really intriguing.

I mean, if traditional theories are correct for how they would

have polished the surface, there's no real reason

that there should be this line.

That line really, to me, looks like a cut mark.

Let me show you something else, which is really interesting.

If you put a horizontal right across the block, what you can

see is that it's a very concave surface.

It's quite nice and uniform.

But you can see it bows significantly in the middle.

NARRATOR: The smoothness of the cut

can only have been made by sawing rather than hacking.

The curvature of the rock suggests a particular type

of saw, an impossibly modern saw.

DR. DEREK MULLER: The most controversial theory

for how this granite slab could have been formed this way,

to have a concave surface, is by cutting it

with a giant circular saw.

It seems amazing, of course, because no circular saws have

ever been found in ancient Egypt.

NARRATOR: This would be astonishing.

According to the history books, the circular saw

was invented at the end of the 18th century.

If these curves can be reproduced,

perhaps it would be possible to deduce how they were made.

At this stone cutting factory near Yeovil, England

they've been trying to find the answer.

PETER BROOKS: They have to have been using a technology that

is more advanced than we give them credit for.

And I'd love to find out what that is.

[sawing sounds]

NARRATOR: Producing the curved profile is achieved

with a modern circular saw by moving

the saw across the stone.

Could an ancient circular saw have cut like this?

[sawing sounds]

But with the saw vertical to the rock,

a straight lip is made at the end.

The Abu Rawash slab has a curved lip,

as if the came in horizontally.

PETER BROOKS: You can see here that if we do a cut straight

onto the surface, you will actually get a surface curve

like that, that you see at Abu Rawash.

But the Abu Rawash slab has this most unusual thing

in as much as a compound curve.

And that can only be done by bringing the blade in at 45

degrees to the surface and drawing the slab along.

That reproduces exactly the pattern

that we see on the slab.

NARRATOR: At an angle of 45 degrees,

a circular saw gives a curved profile

to match the curvature of the saw.

It also leaves a curved lip, whether it's the blade moving

over the block or, more likely, the block being moved

against the blade.

PETER BROOKS: If you have the saw in a vertical plane,

you are effectively moving the block like that.

That's a perfectly easy motion to do if you have some rollers

and some people to move it.

[thrilling music playing]

[sawing sounds]

NARRATOR: But the ancient Egyptians

didn't have electrically powered machinery like this.

And granite has to be cut with either high tensile

steel or diamond blades.

The Egyptians didn't have steel.

And cutting rock with diamond tipped saws impossibly

advanced engineering.

In fact, there's no evidence that the Egyptians had even

discovered diamonds.

If the ancient Egyptians had engineering like this,

history would have to be rewritten.

The intriguing thing now is if you look at those two

curvatures, one in the flat plane and one in the vertical

plane, and you extrapolate those circles back,

you come back to a saw that's about 30-foot in diameter.

And that's very big.

NARRATOR: A 30-foot circular saw.

[sawing sounds]

It would have to have been vertical for slabs of stone

to be easily fed in.

In fact, it would have to have been in some kind of specially

made hole.

PETER BROOKS: So you're looking for a pit in the ground

about 10 or 12 feet deep.

And lo and behold, next door to the slab,

there is a slot in the ground, which exactly matches

the dimensions of a saw that would have

to be used for that slab here.

So I'm saying here is a slot alongside a pyramid that is not

a bone pit.

These slots have been mislabeled as bone pits.

NARRATOR: Could some of these pits

really have contained giant circular saws?

This would be incredible.

And what about the diamond?

No trace of diamond has been found in any excavations.

PETER BROOKS: They weren't looking

for particles of diamond.

So I'm saying that the next time a boat pit is excavated,

a new one they found, I suggest they look very carefully

at the ends and do a very careful analysis of the sand

they find there.

They find the sand contains diamond,

there's your smoking gun.

That's the thing that will prove that were saw pits, not

bone pits.

NARRATOR: But one piece of evidence has been found.

And it's rock solid.

The strongest explanation for the Abu Rawash slab

could be a giant circular saw, strong enough

to cut through granite 4 and 1/2 1,000 years ago.

The extreme engineering of the ancient world

made mega builds that still amaze us today.

2,000 years ago Julius Caesar, one of Rome's greatest

commanders, faced an impossible challenge.

A quarter of a mile wide and 30 feet deep,

the river Rhine from the far bank,

raiding German tribesmen threaten

Caesar's new conquests.

DICK STRAWBRIDGE: On this side, the Germanic tribes

are quite happy.

They believed any advance across the river was impossible.

NARRATOR: But the Germans underestimated the engineering

power of the Roman army and the all consuming ambition

of Caesar.

[whooshing sound]

To understand how the Roman army could bridge a river 2,000

years ago, we are looking at how the British army does it now.

JOHN NAYLOR: Modern armies have access to high tech

bridging equipment.

So to cross this river today, we could use some help

from the royal engineers.

[rock music playing]

NARRATOR: These three high mobility trucks

can deliver an instant bridge anywhere and at any time.

[machinery operating]

This is ABLE, automated bridge laying equipment.

[machinery operating]

10 men can lay this 100-foot bridge in less than half

an hour.

[rock music playing]

But Caesar's bridge would need impossible vital statistics,

as long as four football fields and supporting

the weight of 40,000 troops.

How did to Roman army achieve this impossible task thousands

of years before modern mobile bridging equipment?

[electronic sounds]

There's a fascinating clue here in Ehrenbreitstein Fortress

high above the River Rhine.

DICK STRAWBRIDGE: These very substantial pieces of oak

were recovered from the bed of the River Rhine,

not far from here.

They've been carbon dated back to 50 years BC.

There's only one explanation for that.

These were part of Julius Caesar's bridge.

NARRATOR: These piles driven into the riverbed

reveal the type of bridge Caesar built.

They've been shaped by Roman engineers

so they could be driven into the riverbed.

Well if they've been driving them to the bed,

I'm not sure they're going to come across.

They put pile shoes on the bottom

so it could be driven in without splitting the wood.

It seems almost unbelievable but this nail

was driven in by a Roman engineer.

[wood chopping]

NARRATOR: But these piles were 1 and 1/2 feet thick,

60 feet long, and weighed over two tons.

How did they get them in?

Today, we use pile rigs like this.

It uses a five-ton hammer and can drive 60 miles a day.

PAUL GULLIVER: It's quite amazing the Caesar, 2,000 years

ago, was doing exactly the same type of thing

in order to get over the River Rhine.

[machinery operating]

Just think about the size of this engineering challenge.

You've got to drive supports into the bottom of the river.

You've got to put beams across.

And then you've going to build a road on top of it.

But the supports were massive.

You couldn't just knock them in using a big hammer.

NARRATOR: It seems impossible to believe.

But Roman soldiers built their own pile drivers.

DICK STRAWBRIDGE: A system like this, it uses gravity.

At the top, we've got a great, big granite

block that gets pulled up on a block and tackle.

Let it go, badonk, thumps and drives it into the ground.

They had their tools.

They had trees.

They made this.

It's beautiful.

NARRATOR: And these amazing pile drivers could float.

[machinery operating]

When we look at modern military engineers constructing

a bridge, the principles haven't changed in 2,000 years.

PAUL GULLIVER: The lessons come all the way back from Caesar's

time.

As this rolled out in sections and another section was dropped

in, that's exactly what Caesar's army did.

NARRATOR: This amazing bridge created

from the forest advanced across the River Rhine impossibly

fast.

It took just 10 days.

PAUL GULLIVER: 10 days.

It must have been absolutely astonishing to the Germans

across the river.

A bridge that, in effect, secures the borders of Rome.

NARRATOR: To defeat the strong currents of the Rhine,

Roman engineers created design features we can still see today

in modern beam bridges.

You may think initially that what you should do

is put them in vertically.

No.

The Romans had a cracking idea.

You put them in an angle.

That's upstream, so the force of the water

is pushing them even more into the bed of the river,

making it stronger.

NARRATOR: For the terrified Germans,

Caesars bridge was an unimaginable display

of extreme engineering.

But that didn't stop them from attacking it.

The Germanic tribes realized they could float

logs down the river to try and take out

the bridge that was being built. And to get over that, what

the Romans did was put piles in upstream just

to deflect and slow down any logs that were sent down to try

and wipe out the bridge.

NARRATOR: With the bridge complete Caesar led his troops

to face a German army that outnumbered him 10 to 1.

But the awestruck Germans fled.

Caesar's bridge enabled him to subdue the German tribes

without having to fight them.

This intimidating feat of extreme engineering

wasn't just a mighty bridge.

It was the ultimate strategic deterrent.

DICK STRAWBRIDGE: It was a phenomenal bridge.

Put that into context.

During the Second World War, a bridge

was put across the Sangro river in Italy.

Slightly less, just over 100 feet,

and it took them nine days.

So in Roman times, 1,300 feet, 10 days.

Second World War, nine days.

[thrilling music playing]

PAUL GULLIVER: This really was a massive statement

by Caesar and his armies.

This was we are Rome.

We can go where we wish.

Bow down before us.

[thrilling music playing]

Today's deepwater ports are amazing feats of engineering,

built to accommodate huge container ships and millions

of tons of cargo every year.

DR. LARRIE FERREIRO: We're here in the port of San Diego.

Ports like this are really the lifeline of a nation.

Cargo from all over the world comes here.

This is one of the most important points on the West

Coast of the United States.

NARRATOR: But ports were even more important

in the ancient world.

Whole empires depended on them, and none more so than Rome.

And the Port of Rome, being the greatest of its kind,

is simply known as Portus.

MARY-ANN OCHOTA: Portus was the major seaport

that served the imperial city of ancient Rome.

It was about 20 miles outside the city.

But it was linked to canals that took grain and other cargo

directly into the heart of the city.

NARRATOR: But there was one significant difference

between Portus and many of our great modern harbors.

Portus was man-made.

DR. LARRIE FERREIRO: San Diego is a natural harbor,

one of the best harbors in the world.

Unlike San Diego, most of the areas around the Mediterranean

had no natural harbors.

Portus had to be built by hand to make it

every bit as important as this harbor right here.

NARRATOR: To build a harbor by hand

is a mammoth engineering feat.

And for the Romans to achieve this 2,000 years ago

on the scale of Portus is a seemingly impossible

achievement.

MARY-ANN OCHOTA: The harbor infrastructure at Portus

was incredibly sophisticated.

The main basin was almost 22 million square feet

in surface area.

It had wharves and jetties, a shipbuilding area.

This was fantastic engineering.

NARRATOR: The scale is simply astonishing.

And to try to get a sense of it, at the University

of Southampton in England, they're

using the latest computer imaging techniques

to recreate the ancient port.

DR. GRAEME EARL: It's very much as if we're

walking around the sites of Portus,

even though at the moment, we're based here

in the lab in Southampton.

NARRATOR: Data from geophysical surveys, laser imaging,

and photos taken from drones are all fed into computers.

This is cutting edge archaeology.

And what they've unearthed is awe-inspiring.

We're talking about something at an incredible scale.

For the visiting provincial and their seagoing ship,

this was the first sight of Rome this was meant to really knock

you for six and say oh my God, I'm really arriving

in the center of the world here.

NARRATOR: There was the massive Imperial Palace at least three

stories high.

And this ship repair building, impossibly big, nearly 800 feet

long.

DR. GRAEME EARL: This is an absolutely enormous building,

truly awe-inspiring.

CHRISTINA TRIANTAFILLOU: The logistics, the manpower,

the scale of everything involved is quite overwhelming.

NARRATOR: Portus wasn't the only artificial harbor

in the ancient world.

Incredibly in the third century BC,

a huge harbor was made at Carthage on the North African

coast--

at that time, Rome's great rival.

It was big enough for over 200 ships

to be built and serviced there.

The outer part was for merchant ships.

And then there was a hidden inner harbor for warships.

But typically, the Romans took things to another level.

Portus was over 10 times bigger.

Why did the Romans go to such superhuman efforts?

Why it was such a huge port needed?

In the first century, it's estimated

that the population of Rome was about a million people.

And that was too many mouths to feed from just the surrounding

agricultural land.

So they needed to import grain into the city.

And that's where Portus was key.

NARRATOR: To prevent food riots, vast amounts of grain

were imported from Egypt and from Sicily.

MARY-ANN OCHOTA: If you keep the people fed,

you keep them happy.

If they're starting to get hungry,

if there isn't food available, if the shops are empty,

there's trouble.

NARRATOR: As the empire waned in the sixth century, so

did the use of the port.

And it began to silt up.

Eventually, buildings fell into disrepair.

But seeing the port come alive again gives us

a sense of the reach and might of Roman power at its height.

DR. GRAEME EARL: The amazing thing about Portus

is the scale of remains that we have to encounter there.

And in turn, they give us a way into understanding

the sheer scale of the Roman Empire

that it was at the heart of.

NARRATOR: The greatest empire needed the greatest port.

And they wanted everyone else to see that they had it.

MARY-ANN OCHOTA: That's why they put so much effort,

and invested so much time and engineering skill into Portus.

They created one of the masterpieces

of the ancient world.

[awe-inspiring music playing]

Rome excelled in extreme engineering.

But hundreds of years before Roman records, this tunnel

was built without power tools, without tunneling machines,

without dynamite.

And these ancient engineers surveyed so accurately

that to this day, we don't know how they did it.

[electronic sounds]

This is Lake Nemi, 19 miles South of Rome, Italy.

Every year, rainwater flooded the lake,

making rich, agricultural land unusable.

To solve the problem, ancient engineers

achieved the impossible by tunneling

right through a mountain.

DR. DARIUS ARYA: There's a fantastic construction right

over here.

Essentially, it is a tunnel used to drain away part of the water

from the lake.

But you've got a mountain in between.

NARRATOR: It's estimated that this tunnel was started

over 2,500 years ago.

And to speed up construction, the builders

dreamt up an impossible plan.

DICK STRAWBRIDGE: Why not build a drainage tunnel right

through the mountain?

But not only that, let's start at both ends

and see if we can meet in the middle.

Now, that's a major challenge.

Modern engineers struggle with that, but the ancients did it.

NARRATOR: 3D analyst James Dean is using the latest technology

to understand this feat of extreme engineering.

JAMES DEAN: This incredible tunnel

built to drain and regulate the overflow

runs downhill from Lake Nemi into this valley.

Two tunnels were dug, one from each side,

with the aim of meeting in the middle.

The tunnels met just nine feet out vertically.

This tunnel was dug over 2 and 1/2 thousand years ago.

As a feat of human endeavor, it's just incredible.

But it seems totally impossible they could survey it

so accurately.

How did they do it?

NARRATOR: Modern tunnelers use lasers to dig a straight line.

It seems impossible that ancient engineers achieved

this thousands of years ago.

DR. DARIUS ARYA: It is wet.

It is damp.

It is freezing.

And then of course, I've got electric lights.

But what do they have in antiquity?

You had oil lamps, little niches that you just carve

into the side of the rock.

It's pretty pitiful.

NARRATOR: And yet the engineers were astonishingly accurate.

JAMES DEAN: Over a mile, this tunnel

drops 41 feet, an average gradient of under 1%.

It's an extraordinary feat of ancient engineering.

Just two reference charts were dug to make sure they dug

in the right direction.

But how did they get the gradient right?

They might have used this rudimentary Roman spirit level,

a water trough that marked each end

to show the correct incline.

NARRATOR: The ancient tunnelers may have used this

to harness gravity.

JAMES DEAN: We don't even know if this instrument existed

so early.

But we do know they somehow achieved the impossible.

NARRATOR: Whatever methods the ancients used,

the evidence that they achieved the impossible is here

450 feet underground.

DR. DARIUS ARYA: All right.

Now, we got Paolo up there and I'm down here.

And what it represents is the two teams.

So up on top from Lake Nemi, you have the workmen

cutting through and progressing about 3/4 of a mile.

But down below where I am, the other team

was moving more slowly because this stone is so hard,

these basalt stones.

They only move a quarter of a mile.

DICK STRAWBRIDGE: We still don't really know how they did it.

And the two tunnels met inside the mountain,

and there were just a few feet out.

That's without any modern technology.

It's incredible.

And it was 400 to 500 years BC.

It appears impossible, but they did it.

NARRATOR: Regulating the level of the lake

didn't just protect farmland.

[awe-inspiring music playing]

Several years later, the Nemi tunnel

enabled the emperor Caligula to build a vast, floating palace

and a temple to the goddess Diana.

And 2,000 years later, the tunnel

enabled the lake to be drained to reveal Caligula's ships.

DR. DARIUS ARYA: It's incredible to think that you have

this tunnel 2,500 years old or older draining out part of Lake

Nemi with the same tunnel to reveal

the great ships of Caligula.

NARRATOR: Without the Nemi tunnel

to take away millions of gallons of water,

the two greatest ships to survive from the ancient world

would never have been recovered.

[awe-inspiring music playing]

And even today, the tunnel could protect the lake from flooding.

[awe-inspiring music playing]

[electronic sounds]

Today, every great city has a world beneath it.

Tunnels, vaults, sewers, pipelines--

this is extreme modern engineering.

But could there have been underground engineering

1,500 years ago on the scale of a subterranean cathedral?

Surely impossible.

[thrilling music playing]

In modern times, one of the most remarkable

underground constructions was built in London, England

in the 19th century.

I'm here in Finsbury Park in North London.

I'm about to have a look at one of the subterranean wonders

of this city.

NARRATOR: Dr. Bradley Garrett is an expert in the hidden worlds

beneath our cities.

These steps lead to an engineering marvel.

It's an empty Victorian system, an underground reservoir

that provided water for the city above.

Others are still in use beneath London.

And together, they're quite rightly

famed as a wonder of the Victorian age.

DR. BRADLEY GARRETT: This particular reservoir

would have held something like 5 million gallons of water.

This is an incredible piece of architecture and not

only a feat of engineering, but an aesthetically very beautiful

space.

NARRATOR: Incredible engineering like this kickstarted

the modern world.

[electronic sounds]

But on the other side of Europe, there's

a modern city with an ancient past.

This is Istanbul.

And beneath these streets is something extraordinary.

Perhaps our modern engineering isn't so modern after all.

DR. DARIUS ARYA: I'm in the Basilica Cistern, which

in Turkish is known as Yerebatan Saray or underground palace.

And this is the largest water cistern in the city formerly

known as Constantinople.

The Basilica Cistern is incredible.

It's massive.

And it could hold up to 100,000 tons of water.

That's 22 million gallons of water.

The walls are 12 feet thick lined with waterproof cement.

It still works.

It still holds water.

NARRATOR: Today, this would be an astonishing feat

of engineering.

But incredibly, this cistern is Roman.

The groundbreaking sixth century construction

was overseen by the Roman emperor

himself, Justinian, successor to Constantine,

and a man eager to make his mark.

MARY-ANN OCHOTA: It said the Basilica Cistern was built

by 7,000 slaves all under the command of Emperor Justinian

himself.

This was engineering on a monumental scale.

To think that they undertook such a grand building project

with basic and simple tools methods is beyond belief.

To a modern engineer, you think you just

wouldn't be able to do it.

DR. DARIUS ARYA: How did they build it?

What was the engineering that was involved?

Well, he essentially had a massive labor force

that dug out this space.

We're talking about men using pickaxes and shovels and wicker

baskets to haul away the dirt.

What's even more impressive, of course,

is that that simple kind of technology, what

they had available to them, still

allow them to build greatness.

This is like a cathedral.

NARRATOR: The cistern could be a temple to Roman engineering.

In fact, many of these 336 marble columns

came from disused temples across the empire.

DR. DARIUS ARYA: The Romans are recycling a lot of marble

for the cisterns.

They also recycled this, a great discovery.

And it is a medusa.

This is one that wards off evil in pagan times.

She's placed here and stacked with other blocks

to get this smaller column up to the full height of the ceiling.

Is there some hidden meaning in the fact

that this head is upside down?

Well, the thing is this was in the cistern

in the sixth century.

It was underwater.

Beyond that, we don't know.

[thrilling music playing]

NARRATOR: But why have a water supply underground?

Other cities were supplied with water from reservoirs,

aqueducts, and canals.

The Romans were experts at this.

A few years before, the Romans in the East

had found out the hard way the value

of systems in times of war.

For months, Jewish rebels on the hilltop fortress of Masada

had held out against a massive Roman force.

And they were able to do so because the underground cistern

provided them with enough fresh water to endure the siege.

In Constantinople, the Romans were determined that they would

have a secure supply of water in the heart of the city.

DR. DARIUS ARYA: The city is impervious to attack.

So if they're being besieged, they're

going to have a massive water supply.

They've got that large supply they can withstand attack

for a very long time.

It's a great engineering solution.

And you wouldn't see a water supply on this scale

for another 1,400 years.

NARRATOR: Constantinople may have had the biggest,

but it wasn't the only city in the ancient world

with underground cisterns.

MARY-ANN OCHOTA: The people of Alexandria

did exactly the same thing.

They built cisterns under their city.

Just goes to show how clever all these ancient civilizations

were, and how good they were at engineering solutions

to the problems.

NARRATOR: The Basilica Cistern remained

unparalleled until well into modern times.

This is extreme engineering at its best.

MARY-ANN OCHOTA: It's astonishing to think

that their work wasn't bettered for 1,500 years.

[awe-inspiring music playing]

NARRATOR: Ancient engineers set the standard for technology

that forms a vital part of our modern world.

From sophisticated navigation systems to precision cutting

and ultra modern seaports, proving that the ancient world

was able to achieve the impossible, creating

extreme engineering that can still take your breath away.