Original subtitles

DR MICHAEL SCOTT: The world's ancient cities still contain

many surprises and treasures hidden from view for centuries.

Now, with the latest scanning technology,

I'm revealing the secrets of three of the most fascinating cities on Earth.

Cairo, the gateway to ancient Egypt.

Istanbul, the crossroads between Europe and Asia.

And in this programme, Athens, the birthplace of democracy.

Today, Greater Athens is home to almost four million people.

It's a city that has exploded with life over the past century

and, as a result, ancient sites and monuments

sit cheek by jowl with modern architecture and urban renewal.

It's an intoxicating mix of ancient and modern clashing together.

The temples of ancient Athens dominate the city skyline,

but I'm also exploring its hidden secrets,

buried deep beneath the modern streets.

I thought I knew Athens,

but I've never been in a place quite like this.

I'll be working with our 3-D scanning team...

We're going to be scanning the edges of the water

so we're going to take to the air.

...to reveal the secrets of Athens' ancient past...

...and to explore its brilliant golden age.

In which the citizens of Athens created an idea

that we still cherish over 2,500 years later.

Democracy.

I'll be exploring ancient silver mines...

What a world.

- Whoa! - Whoa!

...and using virtual reality to discover this amazing city

in a whole new way.

You wonder what they've been staring at for the past 2,500 years.

Athens is a city with layer after layer of history and mythology.

The ancients knew this place as the City of the Gods.

Welcome to Invisible Athens.

The Acropolis - a sacred hill in the centre of Athens.

5,000 years ago, its cliffs offered protection

to Bronze Age settlers,

and in the centuries that followed,

the city grew up around it.

At the end of the sixth century BC,

a remarkable event took place here.

The people of Athens overthrew a tyrant on this hillside

and started to create the world's first democracy.

In the golden era that followed, the Athenians built

the beautiful monuments that sit here today.

I'm walking through the Propylaea, the ancient gateway to the Acropolis.

It was designed to funnel your vision down

until it exploded out again

to reveal one of the most important buildings in human history.

The Parthenon.

It was built to honour the goddess Athena,

and on first impressions, this beautiful temple is a model of order and symmetry.

But when you look closer, it becomes even more impressive.

And that's because there's barely a straight vertical line on it.

Each of its 46 columns curves out

and then tapers almost imperceptibly inwards as it rises.

This architectural trick is what gives the Parthenon

its grace and power...

...and creates the illusion of a temple always reaching for the heavens.

It's not just the beauty of this building that strikes you.

It's the powerful message and purpose that it was intended to convey.

It's civilisation versus barbarism,

with this building and the city that it's at the centre of

as the beating heart of civilisation.

Sitting in the shadow of the Parthenon is another, smaller temple.

It's often overlooked, but it's no less significant,

and we're going to find out

why this is one of the most important buildings of ancient Athens.

The Parthenon is renowned for its symmetry,

but the same cannot be said of its eccentric little brother

just across the way.

This is the Erechtheion today, but in ancient times it was simply known as

"the building in which the statue of Athena is".

But it's also the most asymmetrical building in ancient Greece.

It's all different bits of architecture that have sort of been higgledy-piggledy

smashed together in all sorts of weird ways.

And so the question is, why did they design a building to look like this?

Our 3-D scanners are going to try to make sense

of this intriguing temple.

The team is led by architect Matt Shaw.

So, Matt, we've got this uniquely asymmetrical building.

How are we going to tackle that with the 3-D laser scanning?

Well, you have this complete clarity over there with the Parthenon

and here, you're right, this complexity and almost this confusion,

so the first thing for us to do is just to map it really well,

to understand the geometry of the Acropolis site itself,

and then we'll see exactly how the Erechtheion is embedded into that site.

To reveal more about the Erechtheion's setting,

Matt and his team are going to create a 3-D model of the whole Acropolis.

Using thousands of aerial photographs

and a digital process called photogrammetry,

they'll be trying to reveal why the Athenians

designed the Erechtheion in this way.

And while they get to work, I'm going to take a closer look.

The temple gets its name from Erechtheus,

a mythical king of Athens.

He's said to have been killed here by a thunderbolt thrown by Zeus,

king of the gods.

This confusing building becomes even more confusing

when we realise that the ancient Greeks purposefully left a hole in the roof

and a hole in the floor.

The mythical explanation for this

is this was the point where Zeus's thunderbolt came from the sky

and killed Erechtheus.

But the connection with Greece's ancient myths doesn't end there.

This temple also stands over one of the crucial spots

in Athenian mythology -

the contest between the gods to be the patron deity of the city.

Poseidon, the god of the sea, and Athena, the goddess of wisdom,

had to pit their powers against each other.

Poseidon supposedly struck down into rocks

with his trident.

And he produced sea water out of nowhere.

Not to be outdone, Athena planted an olive tree near the same spot,

and the Athenian king who was judging the competition

thought that an olive tree would be more useful to the Athenians

than sea water, and so declared her the victor.

From that moment on, Athena would be the patron deity of Athens.

Today, an olive tree planted in 1917

marks the spot where Athena's olive tree once stood.

Jutting out of another side of the building is a porch

supported by columns in the form of six maidens, known as the Caryatids.

This porch, too, was built over more sacred royal ground.

We're so used to thinking of the maidens acting as columns,

but actually they were guardians of something far more important.

Deep beneath their feet, deep down in that corner,

the grave, the mythical grave of the founding king of Athens, Cecrops.

And so these maidens are doing far more than just holding up the roof above them.

They're there in eternity,

pouring offerings to this legendary hero.

These buildings on the Acropolis

have become enduring symbols of the city that gave the world democracy.

But to Athenians, these were sacred places for religious worship.

The political heart of their city lies elsewhere.

Sitting just below the Acropolis is a hill called the Pnyx,

and it's my favourite place in Athens.

Athenian citizens assembled on this hillside to hear speeches

and cast their votes, and if anywhere can lay claim to being

the world's first democratic meeting place, then this is it.

But this wasn't democracy as we know it.

Only Athenian men were classed as citizens.

There were no votes for women, nor for Athens' vast workforce of slaves.

But while we wouldn't recognise Athenian democracy as democracy,

they also wouldn't recognise our system as democracy,

because we don't each individually get up and vote on every issue

as the Athenians did, and it was on the Pnyx

that the very essence of their political system was put into operation -

a direct vote by every citizen on every issue.

Our scan team will be helping to reveal the story of the ancient city

that lies beneath the surface of modern Athens.

And now they're ready to show me the first scans of the Acropolis.

I can't wait to see Athens in all her glory,

and particularly the Acropolis.

Well, take a seat, and here we are.

You can take this kind of helicopter ride around the site here.

MICHAEL: Yeah. And of course our eyes are immediately attracted

towards the Parthenon, the glory piece of the Acropolis.

And there it is - the eccentric little brother of the Erechtheion,

that kind of weirdly designed building sitting next door.

Let's take this model apart a little bit, so we're going to...

...we're going to take the Erechtheion away

and we'll just be left with the foundations

and the marks on the ground, I guess.

And here we are.

We take ourselves back in time to before that building was even there.

What we're left with is this piece of quite undulating terrain.

This is not a flat site here.

From the south side to the north side,

you can see there's this big drop in terrain here - this is over three metres,

so the site is pretty constrained.

So it's got... It's got difficulties of terrain.

What about also the pre-existing sacred locations

and places that we know were littered around here?

So the first of those

is this strange little hole in the ground, actually, here.

Well, I mean the ancient sources talk about it was Zeus's thunderbolt.

There are moments in time and there are specific locations

that are really attached to the ground itself.

Let's take this little sacred moment on the ground

and let's bring in some of the architecture.

So we've just popped the North Porch on in a matter of seconds,

but we can see this hole in the ceiling that is directly above,

and it frames this patch of ground with this sacred hole in the middle of it.

It's how the Athenians would have thought about

what they were building, that it was visible to the all-seeing gods.

But there's something stopping them extending the building.

(LAUGHS)

- It's the olive tree. - It's the olive tree.

What are you going to do about that?

You can't move this olive tree, supposedly Athena's olive tree.

- You're going to have to work around it. - Yeah.

And I mean, we do this nowadays, right? We have tree preservation orders.

- "You're not touching this." - "This tree's not going anywhere." No.

If we take a sneaky peek beyond Athena's olive tree,

there's another sacred site.

And so this is the Caryatid Porch, isn't it,

that's sitting over the top,

we think, of the tomb of Cecrops.

Again, the building has to respect it

and it has to be commemorated in some way, and marked.

It's layers of history and identity and construction.

It's the constraints of the landscape,

but it's also the constraints of the sacred places

and objects they want to respect.

A patch of ground touched by the gods,

an olive tree created by Athena,

and the tomb of Athens' founding king.

Three sacred spots united around a central temple

housing shrines and relics to Athena and many other gods.

So when you factor all of those things in,

this building becomes an ingenious solution to the problem.

Looking at this building, this little...this little gem here,

no longer is it the sort of eccentric little brother,

it's actually the prime example

of what the Athenians could achieve.

(MERCHANTS SHOUT IN GREEK)

Today, modern Athens is a vivid and colourful city

with a strong connection to the sea.

It's the bustling capital of a democracy

struggling to keep up with its European neighbours.

At the time of the first democracy,

before the buildings of the Acropolis rose up,

Athens also had to fight to secure its place in the world.

In 490 BC, Athens was a Greek city state surrounded by rivals.

Places like Aegina, Corinth

and the militaristic Sparta.

The greatest threats of all, however, lay to the east,

where the Persian Empire was growing in power and ambition.

But Athens had one great advantage over many of its rivals.

The territory it controlled, known as Attica,

was rich in natural resources.

And beneath these hills, in the region of Laurion,

lay extensive seams of silver.

This was once an industrial landscape

teeming with slaves.

And the best way to explore what this world was like

is to go inside one of the mines.

- Shall we go in? - Yes.

- Watch your head. - Watch my head, OK.

My guide is archaeologist Professor Andreas Kapetanios.

He knows these mines better than anyone.

When they started digging galleries...

Those are the galleries going back there?

Some of the galleries, they are like octopus tentacles

and, er, they expanded all over the underground world

because they tried to figure out where to look for the ore.

- And that's where we're going? - Yeah.

OK, well, I'm going to follow you, OK?

Because I certainly don't want to get lost down here.

We have to crawl here.

Narrow and low.

- Michael, are you coming? - I'm on my way...now.

These are actual tunnels

that they would have dug in ancient times

- looking for the silver as they went? - Looking for the ore

that the silver comes from. If you come over here

you will see the deep, um, tool marks.

The tool marks all around.

This gap here, this tunnel is no more than half a metre in height.

I can't imagine how anyone has the work space to move

and then actually work at hacking away at the rock with tools.

I mean, it's incredibly tight.

Andreas, it feels like we're heading downwards now.

You see, this is a kind of step,

- stepping downwards... - Yeah.

And we find ourselves in a hole.

I'll try it head first, and hopefully we won't be in too much trouble.

My God.

Andreas, this is probably the narrowest piece.

ANDREAS: It's fine, it's fine.

- (LAUGHS) It's fine? - Yeah!

This is officially insane.

I have to admit, though, I'm kind of enjoying it.

(LAUGHS)

- ANDREAS: Are you through? - I think I'm through.

This is incredible!

Are you coming?

It's sobering to think that the people who dug these tunnels

2,500 years ago were forced to work down here

for the benefit of the city of Athens.

ANDREAS: This was labour done by tens of thousands of slaves.

Slaves were captured in wars or they were bought in markets.

Slaves were very valuable - valuable tools.

We can see pairs of adults and children working together.

- Children? - Yes, yes.

Can't help but feel for the people who had to work hard

excavating down here in antiquity.

You're seeing the real underbelly, the real Athens.

With all these tight tunnels and narrow galleries, this is going to be

the hardest challenge our scan team have faced yet.

- I do think we've got a while in here. - Yeah.

I think we've got about six hours, probably.

Really? How are you guys going to manage getting all your scanning equipment

through some of these galleries?

I mean, it's teamwork, right? One of us has got to creep through these holes

and the other one has got to pass the equipment

and then we've got to creep again and pass again and creep again and pass again.

I'm now incredibly curious to see some of this silver ore

as they would have seen it as they hewed it out of the rock.

I can show you a piece.

Wow!

Oh, it's sparkling. It's beautiful, isn't it?

And this is what they were after.

But you need four tonnes of this to produce two kilos of silver.

That's why they should move mountains of this material.

These are the Silicon Valleys of classical Athens.

Our scans reveal a labyrinth of tunnels and chambers

over 100 metres long....

...cut by hand as the slaves followed a thin seam of silver ore

into the hillside.

And above ground, the scans also capture

the remains of the mine's processing plants.

Here, the ore would have been washed,

then ground into tiny pebbles

before being heated in furnaces nearby

to coax out the precious silver.

This is just one of at least 30 known silver mines

hidden under the hillsides of Laurion,

and the sources record that in the 480s BC

the Athenians hit on a new and extremely rich vein of silver

which would prove a massive boost to Athens' new democracy.

(CAR HORN TOOTS)

How to spend this lucky windfall

became a subject of fierce debate amongst the citizens of the city.

Many wanted to cash in

and give every citizen an equal share of the silver.

But one leading politician, a heroic general called Themistocles,

put forward a powerful case

for investing the money in a fleet of ships to defend the city.

The debate over what to do with the Laurion silver

was decided by a democratic vote,

and as a result, the people poured the money not into their own pockets,

but into the building of a fleet and, henceforth, naval muscle and might

would be just as important a marker of Athens as the democracy itself.

The naval muscle took the form of warships known as triremes,

because they were powered by three rows of oars.

At 40 metres long, they were light and fast,

and fitted with bronze battering rams.

They were formidable weapons of war.

Here on the waterfronts, we can peel back the layers of history

to show the strategic importance of the Athenian fleet to the city

over several centuries. The scanning team is already investigating.

So how are we going to make the invisible visible this time?

Scanning on the inside, relatively easy,

but we're not just doing the ruins,

we're actually doing this whole apartment building here.

And then we're going to be scanning the edges of the water here,

but getting a view into the water is tricky for us.

So we're going to take to the air for that,

so we want to see directly down through that water

with a nice high sun, and we're hoping that the structures

underneath the water are really going to come to life for us there.

While the scan team gets to work outside,

I'm going to look inside with marine archaeologist Dr Bjørn Lovén.

So, Bjørn, we can see the harbour just there in front of us,

but where can we get a glimpse of the ancient harbour?

Bjørn has investigated the remains of ancient dry docks,

known as ship sheds, tucked away in this basement.

What a magic, hidden, invisible world underneath...

...underneath this apartment.

BJØRN: Yeah - we're so lucky that this has been preserved.

Dry-dock ship sheds like this one seem like a simple enough idea,

but they were vital to the success of Athens' naval fleet.

BJØRN: The best way to show this,

- that if you stand on this column here... - I'll get, OK, I'll get up on this one.

Then, er, over here to the other side.

So in this space between us is one ship shed unit.

So if I go and stand...

If I'm here, I am where the ancient trireme warship...?

Yeah, you are in the space.

So it really is like a massive parking garage?

It is.

And we have to imagine that people are pulling the ships up by hand?

Yeah. What we actually have here,

we have to imagine that right here there would be a line of 70 men...

70 on this side, 70 on that side, all pulling away?

Hauling away on big ropes that were attached to the ram of the ship.

So they would want to pull the ship up out of the water,

not just for repairs, I presume, but also to dry it out?

Yeah, the drier and the more well-maintained your ship is,

the faster it is in battle,

but the most important thing is that they

pulled the ships out of the sea to protect it from the evil ship worm

that could actually destroy a ship in a matter of months.

So it was to ensure that it was a long-lasting,

perfectly functioning lethal weapon?

Yeah. You could say that the fleet was the backbone of the Athenian democracy.

What's becoming much clearer to me now is how, in the ancient world,

it was these industrial, commercial areas down on the ports,

these ship sheds, where the engines and motors of Athenian power and democracy

were housed and maintained

that was the ultimate symbol

of both the democratic political system of Athens

and the power it projected across the ancient world.

Our scans show how the modern apartments

are built right on top of the ancient ship sheds.

And using data gathered from our drone,

we've been able to map remains

that reveal how the ship sheds extend under the modern road

and into today's harbour.

And our graphic shows how they once stood all around this cove.

In 480 BC, thanks to their wise investment,

the Athenian navy was 200 warships strong,

just as Athens prepared to face a mortal threat

from the most powerful empire in the ancient world.

Down here in Piraeus, Athens' port,

a decisive sequence of events began.

An army of at least 200,000 Persian soldiers

was on its way to invade Athens and crush its democracy.

And with the entire population at risk,

the Athenians had to decide whether to stay and fight in the city

or to retreat by sea.

Themistocles knew the Athenians could never hope to take on

the full force of the Persians on land,

and so he convinced them to make an extraordinary decision -

to abandon Athens, to abandon the land of Attica

and instead to put all their hopes of survival

into the wooden walls of their ships.

And on that moment, that decision, that democratic vote did history turn.

Women and children were taken to safety

and every Athenian man of military age

took his place on a trireme

and prepared to face the Persians at sea.

The Athenians withdrew their fleet

just a short distance across the water from the city

into a secluded bay where they could plan their next move.

Here, they were joined by allies from across Greece,

and in late September 480 BC, they prepared to make a stand.

The battle that followed, the Battle of Salamis,

was the moment the world's first democracy faced its greatest threat.

It is one of the major turning points of Western civilisation.

And until recently, barely any remains

dating from this moment were thought to have survived.

But, in 2017, Professor Yannos Lolos discovered new evidence

that helps us to understand what this bay might have been like at the time.

YANNOS: On the eve of the Battle of Salamis,

the united Greek fleet was stationed in this bay

with over 300 triple-decker warships.

You've been investigating here out in the bay.

What have you found here?

We have constructed the first underwater geological map of the bay,

of the harbour, of Salamis.

This is the harbour of the city state of Athens,

this is a fortified harbour,

including a long wall with a round tower at each end.

There's no doubt about the crucial role of this harbour

on the eve of the sea battle of Salamis.

We can imagine the Athenians,

who see from the heights surrounding this bay

- their city in flames... - It's just there behind us, isn't it?

I'm trying to imagine the fear, the anger,

the desperation that the people in this bay must have felt...

- Yes, yes, - ...at that time.

Because Athens was no longer.

Using the new research, our scan team has managed to fix

the coordinates of the archaeological remains here.

Our graphic model of the harbour wall and its defensive tower

shows how it extended 160 metres into the bay.

And this is where the force of over 300 Greek triremes gathered

to take on a Persian fleet said to be three times as strong.

To help balance the odds, the general, Themistocles,

managed to lure the Persians into the narrow straits beyond the bay,

where their superior numbers would count for nothing.

As the massive force funnelled into the narrow stretch of water,

the Athenians and their allies pounced,

rammed into the enemy ships

and smashed the Persian fleet apart.

It was a stunning victory for the world's first democracy.

But victory came at a high price for Athens.

The people returned to a city in ruins.

Even their sacred buildings on the Acropolis had been razed to the ground.

In the decades after the Athenians defeated the Persians,

they did something really quite extraordinary.

Instead of rebuilding their city,

they chose instead to leave it in ruins as a memorial,

as they put it, to the impiety of the barbarian.

And yet, while they would happily leave their city in ruins,

the Athenians moved as quickly as they could

to build something else entirely to protect themselves in the future.

And that's what I'm trying to find here in the streets of Athens today.

And I think...it's somewhere around here.

I've been told to take a left at the loos,

and now I'm looking for some stairs downwards.

And here they are.

This you don't see every day in a car park.

These are 2,500-year-old city walls.

The Themistoclean Walls of Athens.

You can still see the...

...the individual blocks neatly lined up on top of one another,

and we've got here... We've got one course, a second, a third,

a fourth, a fifth disappearing into the floor,

and we're yet nowhere near the foundations.

They must be even further down.

The story is that every Athenian was told to drop whatever they were doing

and come and help build the walls,

and in the foundations, they put anything they could find.

There's column drums in there, sculptures, gravestones,

anything that would help this wall rise up as quickly as possible.

Our scans and graphics show that these walls,

concealed within the modern car park,

were part of a series of building projects

that would transform Athens.

First, the Athenians enclosed their city,

then, almost ten kilometres away, they fortified the port of Piraeus.

And then they linked the two

with a fortified corridor that ran all the way

from the ports to the centre of Athens,

a system of long walls almost 150 metres apart

and estimated to be 3.5 metres high.

With the completion of the Long Walls connecting the port of Piraeus

to these walls guarding the city,

Athens effectively became an island on the mainland.

No strictly land-based force could really ever hope to conquer it.

And as a result, to many, Athens seemed impregnable.

A bit narrow... Whoa! ...and into the water,

Let's see if we can get through this.

When the ancient Athenians

eventually did decide to rebuild their city,

they wanted to do it bigger and better than ever before,

and so they turned to the very landscape around them,

because the land around Athens

is literally made of marble.

Although we're obviously driv...

- (CLUNK) - (LAUGHS)

...just driving on, it's like we're driving on a marble road.

We're driving on Penteli Mountain

and it was here that the Athenians came to quarry.

The quarry face that dates from that time is still here.

And archaeologist Alexandra Mari is going to show me.

And what were your impressions when you first saw it?

I was, er, amazed, actually, by all these things which are here.

- This is it. - Wow! This is the quarry.

- Isn't it nice? - It's extraordinary.

It's huge! I mean, it's massive, you can see

- the sheer walls they quarried off. - The walls, yes, yes.

Can we get any sense of how much marble was quarried out of this space?

Well, approximately 400,000 tonnes of marble

were produced by this quarry - the Quarry of the Cave, as it is called.

And you can see all the cut marks, can't you,

of all the individual chisels moving, moving...

ALEXANDRA: First of all, they had to choose the right block,

without fissures and cracks, and then they would start hammering,

continuous hammering until they managed to split the block.

- But that's incredibly dangerous... - Yes.

- ...and time-consuming and hard work. - Very, very much, yes. Yes, yes, exactly.

What they had to do was, er,

to transport it to a special road called Lithagogia,

meaning conveyance of stones.

And there's nothing left of that road today?

- Well, yes, there is, actually. - There is?

Just a little, a small part.

This was once the start of a long route

that ran from the quarry to the heart of the city over 18 kilometres away.

I mean, it's still beautiful, isn't it, over 2,500 years?

- I mean, it's like a sledge track. - Yes, exactly.

It seems that, er, they were using animal fat

in order to grease the flagstones and reduce the friction.

And the danger that if one block of marble got away,

it would just sweep down the mountain?

And a little further down the hillside

is in fact one runaway block from the quarry above.

But take a look at this view. What do you think about it?

Hang on a sec, is this...?

This is a piece of a column.

- It's a column drum. - Mm-hm.

So perhaps somebody did take their eye off the job

and was looking at the view and they missed their rope.

- After all. - And it all went!

This weighed ten tonnes.

Can you imagine having to go back up to the top

to all the workers who have been quarrying this piece of stone

and go, "Sorry, guys, we've got to start again"?

"It just broke," yeah.

A phenomenal sort of marker to an incredible process.

Yes, exactly.

The marble that was quarried here

and transported all the way to the city became the face of Athens' new identity -

that of a place on the cusp of a golden age

of not just art and architecture, but politics, philosophy, culture -

a golden age that still burns bright in our human story.

Our 3-D model shows how the gleaming marble from Mount Penteli

was used to create brand-new monuments over the ruins of the Acropolis...

...the most prestigious of which were the Parthenon, started in 447 BC...

...the Propylaea, a temple to Nike...

...and of course the Erechtheion...

...all completed in one remarkable 40-year burst

of creativity and confidence

in the second half of the fifth century BC.

Athens was now the most powerful city in Greece,

and the Athenian Empire began to extend its influence across the sea.

So, Costas, we have calm seas today, good seas to be out on the boat?

Yes, it's very good weather.

This is Cape Sounion.

It's about 80 kilometres south of Athens

and it's the southernmost tip of the land of the Athenians, Attica.

For the Athenians who'd been out across the Aegean

on trading ventures or military expeditions,

the sight of this place meant that they were finally home.

But something of a mystery has grown up around Sounion.

Thanks to the Temple of Poseidon that sits on the hill,

it was mostly known as a sacred site,

and until recently, that's overshadowed the strategic role

it played in Athens' empire.

Now a team of archaeologists, including Dr Kalliopi Baika,

are discovering how important it really was.

There was a settlement with a very important strategic role

and commercial value,

and here we're standing in front of a very big, massive building, actually.

This is a corner, and the other part of the corner you can see the other way.

So basically I'm standing in the middle of what was once

- a wall going that way... - Yes, a massive wall.

...out to sea.

They didn't build the building half on the land and half in the sea,

- so something's changed? - We have a relative sea-level change

of two metres and a half,

almost three metres, from the fifth century BC.

So what you're telling me is that half of the settlement that was here at Sounion

- is there in the water? - Yes.

- And we can get in and explore that? - Absolutely, yes, we can.

Sounion's crucial role in the defence of the Athenian Empire

is now becoming clearer.

Sounion is the most sophisticated

small-scale naval base in the Mediterranean.

Here, we have a strategic lookout post

that operates in a network of naval bases.

And that means, from here, a ship could reach the message to Athens

that an enemy fleet is approaching in only one hour.

The water is clear,

but I'm having trouble finding the remains of the city.

Yes, the vertical lines, the small structures from this way.

And, finally, here they are.

Massive sections of defensive wall from the submerged city,

still recognisable after 2,500 years.

And one of the berths of the ancient naval base cut into sheer rock.

And fine marble blocks from what must have been impressive structures

in this strategically important town.

It's absolutely amazing down there, as clear as day.

It must have been once upon a time stretching down from the coastline,

now under the water behind me, the remains of a massive wall.

As you come out from the coast, the ancient blocks, they're a decent size,

but they get bigger and bigger till the ones here -

must have been an enormous fortification wall for the ancient town of Sounion.

It feels like a world frozen in time down there.

Fortified naval bases like Sounion

helped Athens extend its empire across Greece,

the Aegean and the coast of Asia Minor.

But its supremacy didn't go unchallenged.

From here on the hill above Sounion you can look out

towards the Peloponnese, home to their bitterest Greek rival -

Sparta.

In the second half of the fifth century BC,

the two cities waged war on and off across this territory for almost 30 years.

Athens relied mostly on its famous fleet to fight its cause...

...while the citizens took refuge behind their city walls.

But in 405 BC, the Spartans finally lured Athens into

a disastrous sea battle...

...and then laid siege to their weakened city.

Athens was forced to surrender the following year.

The golden age of the world's first democracy was coming to an end.

Its ideals and achievements, however, would never be forgotten.

That was partly due to the Athenians themselves,

who eulogised their golden age in the centuries that followed,

but it was also partly thanks to the Romans,

who came to control Athens in the first century BC.

And over the next two centuries Athens became

a kind of theme park cum finishing school for the Roman elite.

In the second century AD, the Emperor Hadrian

was one of Rome's most passionate admirers of all things Greek.

Hadrian didn't just repair bits of Athens,

he claimed the city for himself.

This is the Arch of Hadrian

and there still, just above the archway, you can read a text,

it says simply, "This is the city of Hadrian."

Hadrian was on a mission to improve Athens

and he lavished the city with gifts - a library, a gymnasium,

and something even more crucial to the everyday life of the people.

And that's what brings me here, to the site of the modern Olympic Village.

I'm going to explore a feat of Roman engineering.

Which means going underground...again.

- Tim, how are we looking? - It's good.

I'm just getting the final preparations here.

But you can feel the... You can feel the hot air coming out

from under there. I can't even see the bottom, I've got no sense...

It's about 16 metres straight down.

Just absolutely straight burrowed, down through...

This shaft leads down to a 2nd-century AD Roman aqueduct,

where TV cameras have never been allowed to film before.

Oh, gosh, it's narrow now.

Oh, I can hear the water.

(LAUGHS)

Here we come, into the underground aqueduct.

There we are.

God, I've got not even room enough for me to stand sideways.

Have I got my torch?

Get to start exploring.

There's the water right there, this is extraordinary.

Oh, I'm stuck, I am actually stuck. I'll go more on my side.

I can see the passageway just opening up behind me

is just going dead on.

The water is...

It's cold, it's fresh, it's got that mountain feel to it.

You can see it's doing its job,

bringing the water from the hills around Athens right into the centre.

I'm just trying to imagine the lives

of the people who were actually cutting this out of the sheer rock.

I mean, absolutely appalling conditions.

I'm wondering whether these... I keep seeing these...

They're sort of a little shelf.

This was how they managed to see down here what they were doing.

They had small oil lamps, like my torch, I can put it here,

just giving them enough of a flickering light

by which to hack away at the solid rock in front of them.

(THEY LAUGH)

Can't actually now turn my head back. There we go.

This tunnel took 15 years to dig out of solid rock,

and runs for 20 kilometres.

It's an astonishing feat of ancient engineering.

And I've asked aqueduct expert Dr Shawna Leigh to shed some light on it.

So, Shawna, how did they go about

building such a project so deep underground?

They would dig vertical shafts

something between 33 and 35 metres apart

and, um dig towards each other and ideally meet each other.

What happens if you don't meet the first time?

So, um, you have to do a little S-curve to sort of get it together.

- Just like this one we've come through? - Yes, exactly, right there.

And we're talking about an aqueduct

- of over 20 kilometres in length. - Right.

How did they manage to get that gradient so perfect?

Well, it's absolutely striking because it's all based on gravity,

so if the slope is too steep, the water will move too quickly

and basically tear apart the tunnel.

And if it's too shallow, the water won't move.

And here it is, still flowing beneath our feet...

- Absolutely. - ...almost 2,000 years later.

It's amazing, isn't it?

Oh, and this section's even narrower!

The aqueduct's getting lower and lower, I'm having to go

actually down on my knees

right into the water. Oh!

But the pay-off is this extraordinary vaulted ceiling.

They have these unusual markings from...frankly who knows when?

It's nice to see the sky again.

The scans reveal the aqueduct in amazing detail.

We can see several of those remarkable curves

where the workmen almost missed each other.

The section we scanned was just over 80 metres long

and over that distance, the water level drops less than half a metre.

A gradient so well-engineered

that the aqueduct was used until the middle of the 20th century.

And this is just one part of a network of ancient aqueducts

that runs for almost 80 kilometres beneath the city of Athens.

I've seen so much of ancient Athens hidden

beneath the surface of the modern city,

but now I'm going to experience it in virtual reality.

- OK. - Jump on in.

Oh...can't wait to see what you've got waiting.

Ah, wow!

So this is the Acropolis, of course.

That's the gods' view!

We're, like, flying over the top of the city.

So, actually, we can dive on in a little bit here

and go and have a real detailed view of the Erechtheion.

And this is, I mean, the best doll's house in the world.

- Check this out. - Today you can just

walk into the building.

I can put myself inside it and look at it from this side.

Wow.

So we're back now at a scale that you'll be super familiar with, right?

- The world is the real scale, - This is one to one, wow.

- And actually you are not allowed here... - No.

...in the real world.

We're right down looking up at the whole of the porch, aren't we?

From the hole.

Whoa!

- You've got us flying through the air. - Yeah.

So now we can just drift around the Erechtheion.

We've just been through the door.

Hang on a sec, now we're going into a wall!

There's a wall, whoa, whoa!

Whoa, we just went through the wall.

- Why not, hey? - (LAUGHS)

And here we are.

Oh, wow.

What a view.

You wonder what they've been staring at for the past 2,500 years.

Just step up on there and, er, give them a hand.

What, so if I try to...?

Hang on a sec.

Whoa!

Oh, that is a freaky experience.

That's worse than flying through the virtual world

cos you're actually propelling yourself...

And I'm right... I'm right next to them!

It's like, "Yeah, you know what?

"Easy peasy, no worries."

Do you think you could hold that pose for two-and-a-half millennia?

Well, with a view like this, yeah, it's not so bad.

I think it definitely would have compensations.

Looking out over Athens' glory of the Parthenon,

it's creating this link that was so important to the Athenians

between the landscape, the past, the present, the future.

If there's a spot you put yourself in in Athens

to understand what it means to be Athenian,

this is it.

The Athenians smelted silver from their mines

and voted to invest it in a naval fleet.

They built dry docks to preserve their warships.

They surrounded their city and their harbour with extraordinary walls.

And they gave their city a unique identity

using marble carved from their own quarries.

This bold democracy left a legacy that has never been forgotten.

It's all too easy when you come to Athens to be overwhelmed

by the beauty of the buildings on the Acropolis, the Parthenon, the Erechtheion,

but what's become clear to me is that the hidden and invisible spaces

of the city are just as important -

those mines and aqueducts, those quarries and ship sheds,

those are the spaces in which Athens itself was forged,

its ideas and dreams made real,

and those are ideas and dreams that still inspire us today.