All language subtitles for Ancient.Impossible.S01E10.Extreme.Engineering.1080p.AMZN.WEB-DL.DD+2.0.H.264-playWEB_track4_[eng]

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.