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 going to reveal

the secrets of three of the most fascinating cities on Earth.

Cairo - the gateway to Egypt's ancient wonders.

Athens - the birthplace of democracy.

And, in this programme...

...Istanbul - the dramatic crossroads between Asia and Europe.

For over 2,500 years,

the East has met the West, here, in Istanbul,

the strategic mid ground

fought over by some of the world's mightiest empires.

Romans, Christian crusaders and Muslim Turks

all battled to control this place.

It was once the biggest city on Earth...

OK.

...but many of its ancient treasures are invisible...

Oh!

...buried deep beneath the surface of the city.

- I imagine rats. - GUIDE: Be careful.

Whoa!

I'll be working with our 3D scanning team to explore palaces...

...fortresses...

...and aqueducts.

We'll uncover the forgotten Roman chariot track...

- This was the track right here? - Yes.

...reveal the genius of the city's ancient engineers...

Incredible.

...and explore a masterpiece of Islamic innovation.

And I'll be using virtual reality to see the city in a totally new way.

Whoa. Whoa, whoa, whoa, whoa, whoa, whoa. Whoa, whoa, whoa!

This is Istanbul as even the locals may never have seen it before.

Welcome to invisible Istanbul.

Istanbul...

...the bridge between two continents.

And I'm arriving on the mighty waterway that put this city on the map.

I'm on the Bosphorus, one of the busiest shipping lanes in the world.

Behind me, to the north, is the Black Sea

and in front of me is the Mediterranean.

On my left is Asia and on my right, Europe.

People coming and going from every point of the compass converge here.

And straddling this waterway is the city of Istanbul.

Istanbul's strategic position

made it irresistible to the great powers of the ancient world.

2,500 years ago, it was the Greek town of Byzantium.

The Romans transformed it into the city of Constantinople.

Then, in 1453, it became the Islamic city of Istanbul.

As Napoleon put it, "If the world were a single state,

"then this city would be its capital."

Istanbul's tempestuous history

has created one of the most vibrant cities on the planet.

There's evidence of that turmoil all over the city.

Even the city's most famous places have their battle scars.

The Hagia Sophia, or Church of the Holy Wisdom of Christ, was built by the Romans.

For hundreds of years, it was the biggest cathedral in the world.

Modern buildings often only last for decades.

I'm going to find out how the Hagia Sophia is still standing after 1,500 years.

The height of this dome, the sense of air and space is just extraordinary.

When it was built, in the sixth century AD,

this was the tallest dome in the world -

55 metres above my head.

And the people of the time talked about the way

that it seemed to reach for the very sky itself.

This building dominated the landscape of sixth-century Constantinople

and left its people in awe.

Two previous versions of the Hagia Sophia were destroyed by fire.

So the Emperor Justinian made this one

into a massive statement of Roman power and endurance.

The dome of the Hagia Sophia has faced earthquakes, riots

sieges and conquest.

Our scanning team, led by architect Matt Shore,

is trying to find out how it survived.

- Matt, good to see you. - Michael.

How are you doing?

- This is Tom. - Hi. Tom. Nice to see you.

Great to see the scanner is already in action.

Yep, we've been going all morning.

So, are we going to be able to get an answer to the question, you know,

that always strikes me here, which is - how is this building still standing?

Yeah, I mean, that's the plan.

So, the scanner is firing away over a million points a second.

We're going to create a model of this entire space

that has over a billion points in it.

Wow! So, we're going to be able to visualise this whole thing,

this enormous, enormous structure, and get... Maybe unravel the mysteries?

- That's the plan, that's... - Well, we've been talking big.

But if I can steal you away from Tom for a second if he's in charge...

He looks like he's got it under control.

I've got something small to show you

which is my favourite thing in this entire place.

OK. Let's go.

After 1,500 years, the history of Justinian's cathedral

has become entangled with legend.

Justinian spared no expense on this building, right?

He had stuff brought in from Africa, from Asia

and, of course, across the Mediterranean, and these are his doors.

These are the Emperor's doors,

and the story goes that they're actually made from bits of Noah's Ark.

OK.

Yeah, but, I mean, what he wanted to be was the new Solomon...

Yeah.

...and builder of the first temple of Jerusalem,

and, supposedly, the story goes that when he walked into this place,

when it was finished, he said, you know,

"I have outdone thee, Solomon."

But this is what I came to show you.

- This is the important bit. - This hole?

- This hole, right? - OK.

And the story goes... These are the Emperor's doors.

- This is where the guards stood. - OK.

And these holes in the ground are...

- Years of footsteps. - Years and years.

Hours and hours of the guys standing here on guard.

So, if you want to be kind of in the shoes of the people from the past, right?

You can't get much better than a place like this.

It kind of reminds me of the pacing round the scanner that we do.

- Our little circles, around and around. - (MICHAEL LAUGHS)

On that note, I probably should let you get back to it, right?

I probably should.

- I'm going to head off this way. - Thank you for sharing.

- Good to see you. - Good luck.

In the 15th century, the Hagia Sophia was converted into a mosque

and, later, these minarets were added.

(BIRDS SQUAWK)

It was a church for just over 900 years,

and it was a mosque for just under 500,

and now, it's been a museum for just over 80.

Its strategic position between Europe and Asia has placed it

at the centre of a religious and political tug-of-war

that continues to this day.

The Hagia Sophia embodies the city's turbulent history.

Istanbul will always be pulled between East and West,

it will always have to make a choice

as a result of geopolitics and internal change.

To get evidence of how history has changed the city,

Matt and his team are going to create a 3D map

of the heart of Istanbul.

MATT: We're going to employ a process called photogrammetry.

Taking thousands and thousands of individual photographs...

...and we pump all of those images in and use very clever algorithms.

Then, we're able to compute a really, really accurate 3D model of Istanbul.

MICHAEL: The model will show us a city built, destroyed and transformed

over the last two millennia.

And by scanning the Hagia Sophia inside and out,

we'll discover how it, too, has survived against the odds.

And the first scans are coming in now.

Matt, how are you doing?

How are you doing, Michael? Good to see you.

Can't wait to see Istanbul in all her glory. There she is!

- And there we go. - (WHISPERS) Wow!

- So, this is our photogrammetry model. - Wow!

Unbelievable.

And at the very centre of all of that, as well - Hagia Sophia.

And there it is.

And the really interesting stuff comes when we get ourselves in...

(MICHAEL LAUGHS) We just went inside the building!

Now that's something... I mean, you can't do that in real life, can you?

You can't fly through a wall whenever you fancy it.

Just incredible.

But what do you think the scans have been able to reveal

that we couldn't possibly have known when we were there?

Well, I mean, even inside the scans, your eye is always drawn up to the dome here.

And if we start to navigate our way up there, actually,

immediately, we start to see some slightly strange inconsistencies.

So, the dome is not circular any more.

You get these lumps and bumps in, and what that is,

we're seeing the effects of earthquakes over the years.

But, I mean, it looks as clear as day on that scan,

that there's a big bump area at the top and at the bottom,

but that wasn't visible to us at all in... when we were there in reality.

No, I think it's not filling in any of the gaps that you do with your eye

and, actually, this gets more revealing

when we start to take ourselves outside, and just skim the building here.

So what we're left with here, is just the inner skin of the dome,

and check out some of these lumps and bumps.

Yeah, and they're not just flaws, as well,

I mean, there's an amazing amount

of ingenuity and solution that's on display here as well.

So, you're faced with these incredible situations,

earthquakes trying to pull this building apart.

So, 26 years after it was first constructed, the dome collapsed.

One of the first techniques that was used to...

...when they rebuilt this dome was the series of ribs

that you can see here,

taking the weight down to this circular beam.

And then these crucial triangular structural pieces.

These are called pendentives.

And these transfer the weight from the circle at the bottom of the dome

to four points,

and they turn this structure from a spherical structure

into a square structure.

So, they take that load in four positions down to the ground here.

And when you're there, in the building, you don't

think about any of that, cos your eye is completely taken

to the beautiful angels.

It feels like the angels are literally holding up...heaven, aren't they?

- They're holding up the roof. - Yeah.

And if I actually just pull us back outside the building here,

I can actually slice this building up.

So, we have our dome here.

We also have these two big half domes on the side here,

and what that does is expand that space out.

So, when you walk inside, you really feel this enormous volume.

But even these clever structural systems weren't quite enough.

So over the years, a series of buttresses have been added to every side.

And they're holding it all together, right?

Yeah. They're stopping things from splaying out.

MICHAEL: Our scans can also give us a better idea

of what the building looked like

before the minarets were added in the 15th and 16th centuries.

I mean, that makes this scanning such a fantastic tool, doesn't it,

for historians, or architects, or engineers?

It's giving you the life story of this building,

with all the lumps and bumps

and wrinkles that that brings.

The Roman city of Constantinople was named after its founding emperor, Constantine,

and the Hagia Sophia was its spiritual heart.

The Emperor's seat of earthly power

was built right next to the cathedral.

The Great Palace - a vast, luxury complex in the heart of the city.

This was home to Rome's Byzantine emperors for nearly 700 years.

Today, people drive past the old palace walls without a second thought.

But they were once one of Constantinople's glories.

This, well, rather romantic ruin is the Palace of Boukoleon

and it was part of the great complex of palaces here in Istanbul.

And when it was built in the fifth century, the sea came right up here.

So this was the summer residence,

the seaside annexe, if you will, of the imperial family.

And when it was built, they said that

it was designed to evoke the admiration both of strangers

and of their own subjects, and... I can buy that.

This place had 500 rooms, all with gold mosaics.

I'd be pretty gobsmacked.

And yet, today...

Well...

...that is the best bit that's left.

I've been told I can find a way into the Boukoleon Palace through here.

This feels like something entirely sort of dystopian.

- There's a train line over here... - (TRAIN HORN HOOTS)

...I'm in somebody's garden...

...and here...

...we're back in the palace!

This is... It's like nature has completely taken over this world.

But we have to imagine what this place would have been like in its glory.

This, a grand, echoing state room with marble mosaics -

the treasures and statues beyond measure.

And gorgeous, huge windows looking out to sea.

It must've been quite a sight to behold.

Our graphic gives us an idea of the grandeur

of this magnificent building -

just one part of the Great Palace complex.

Everywhere you go in this part of Istanbul, you stumble upon the remains

of the Great Palace.

(THEY CHAT)

Ferudun Özgümüs, professor of art history at Istanbul University,

is taking me to see one of the most recent discoveries.

But there are some examples of some of the old...

I want to show you under this building in the carpet shop.

In the carpet shop?

- In the carpet shop, yes. - OK.

There was an old building stood here once...

Uh-huh.

...and when they demolished the old building in 2002,

they unearthed, I don't know, by coincidence,

one of the major discoveries of our work in Istanbul.

Oh, OK. Down the basement. OK.

- We've been through the carpet shop... - Yes.

- ...and now... - And now a travel agency.

(LAUGHING) Now a travel agency! OK!

- And now for the kitchen section. - The kitchen, OK. Right.

And now from the kitchen section, we're going deeper.

OK. It feels like a weirdly domesticated

Journey to the Centre of the Earth right now.

Exactly.

But I'm going to show you something very interesting.

Ooh!

Going down, deeper and deeper, and I want to show you...

What's this?

That's a very interesting mosaic floor.

Came to light 2002.

It was a part of a church, and the church itself was a part

of the Great Palace of Constantine the Great.

Our 3D map shows the position of today's carpet shop

inside the walls of the Great Palace.

This must have been an exquisite church.

This is from the late seventh century - mosaic floor...

And it's beautiful. What stunning condition!

And not only this one, and we have something special

that all Eastern Orthodox Churches have, which is deeper...

- Deeper? We can go down deeper? - Yes, exactly.

I mean, literally,

we're going down through the layers of the past here, aren't we? Lead on!

(DOOR RUMBLES)

- So, we're going down. - Deeper.

Oh, my Lord!

(MICHAEL WHISPERS) Oh!

So, we're underneath the seventh-century Byzantine church floor?

Yes.

(MICHAEL WHISPERS) Wow, what a space!

And what I want to show you particularly is...

So, this is what we've come all this way for?

- Yes. - Uh!

So, this is a, what, a freshwater spring?

And that's Byzantine, and Byzantine springs are very rare in Istanbul.

And that water looks so clear!

And what's this? We've got an image here...

How extraordinary. I mean, this makes this a very valuable...

Our scan shows nearly nine metres of layered history

from the ancient spring up through the Great Palace

to the carpet shop in the modern city.

(MAN SPEAKS IN TURKISH)

Can I have one?

Thank you.

The Emperor Constantine moved the capital of the Roman Empire here

in the fourth century.

Yes!

And he wanted to make a city to outshine Rome.

He went on a building spree - churches, palaces, public baths and a library.

And within a century the population soared...

...from 20,000 to 200,000.

The Romans were brilliant at creating public places

where the whole city could come together,

everyone from the Emperor downwards.

Think...the Colosseum in Rome.

And here, in Constantinople, that place was the Hippodrome,

the chariot-racing track.

And I've come to meet someone who knows this place inside out.

- Kerim? - Hi, Michael.

(KERIM SPEAKS IN TURKISH)

Shall we explore? I can't wait to find out more about this.

KERIM: It's my pleasure.

Only these walls remain but there's enough to see how impressive

the Hippodrome must have been.

Where are we now?

We are now in front of the monumental façade

of the Hippodrome's curved end,

- called Sphendone. - Ah.

Would there have been entrances this end?

Yeah. Here, look.

You can here see the... the vaulted archways

forming the entrances and exits.

Now walled up.

The Hippodrome once dominated ancient Constantinople.

This was the social centre of the city...

...holding twice as many spectators as Rome's Colosseum...

...and even more than today's Wembley Stadium.

But little remains of the racetrack.

Can we get a sense of what this place would have been like on race day?

Where would the spectators have been sitting?

Where would the chariots have been racing?

So, we can estimate that...

...the road running around today's square

was almost perfectly following the line of chariot-racing track.

- This was the track right here? - Yes.

So we have to imagine the chariots coming right at us now at full pelt!

- Let's move out of the way, quickly. - It's fantastic...

But that sense of, what, up to 100,000 people, something like that,

- chanting, screaming... - Yes, you're right.

...kind of all cheering on their teams.

- Yes. - Wow.

What a place! And the Emperor watching over it all, huh?

Yeah, he was.

And I've got something else to show you in the underground.

So, Kerim, where are we going?

Yeah, you will see the substructure of the Hippodrome, Michael.

- We're going in here? - Yes.

I guess this is a place the public don't get very often, right?

No.

Come. Follow me.

OK.

Now I see why you told us to bring torches.

- Yeah. - Wow. What a space!

What do you think?

Amazing. Where are we?

This is the substructure of the seating.

So underneath all those spectators cheering away?

Yes, exactly.

And there's tunnels - you can go this way. There's tunnels that way.

My God, it's a rabbit warren down here.

- Yeah, you'd better follow me. - OK. I'll definitely follow you.

I guess we have to imagine people were getting to their seats,

- all the services.... - Yes.

What else happened down here, do you think?

There's also a story about this concealed space used as a prison or for...

- ...for the execution. - Wow.

For instance, we know from the sources, Justinian II was tortured

by his rebellious subjects in the seventh century.

It happened probably here.

To repay his despotic rule, they sliced off his nose and cut out his tongue.

And after banishing for ten years, he returned.

MICHAEL: He returned?

KERIM: Having to hide behind a solid golden mask replacing his nose,

he continued ruling over the population until his own army turned on him.

This time, they cut off his head to make sure that he wouldn't come back.

MICHAEL: Amazing.

And what's through here? My God, you can go...

There's tunnels, there's ways here, here...

There's a doorway here, Kerim? What's...?

Yeah. See it yourself.

- Through here. - Go on, go ahead.

I'll go ahead, shall I? OK.

Wow! OK.

Er...Kerim?

I think we're going to need a lot more gear.

(GRUNTS)

Well, don't I feel good?

To be honest, I feel like a trussed-up chicken but...

I think I'm ready. Kerim?

- OK, let's go. - OK, let's do this.

Kerim is going to show me how the Hippodrome was cleverly adapted

to help the city survive.

I clip on...

(SPLASHING)

Is it cold?

- Oh! OK. - Be careful.

OK. Yes, the steps are slippy.

It feels like there's quite a few rocks under our feet but...

(TAPPING)

Wow, this place is huge!

KERIM: Yes.

MICHAEL: It's extraordinary.

But how are we suddenly in such an enormous space?

KERIM: Yeah, because this vaulted chamber was converted into a cistern.

Probably in the sixth century.

So they completely just repurposed this entire...

- Yes, exactly. - ...area? Wow.

The city is surrounded by the sea,

but it has very few sources of fresh water.

Saving every drop was essential.

So the Romans transformed the Hippodrome's passageways

into this massive reservoir.

This vaulted space alone could hold ten million litres

to save the city in times of siege or drought.

And all thanks to the Roman invention of waterproof cement.

KERIM: This is the hydraulic plaster, the waterproof plaster.

MICHAEL: It's good plaster! It's still here.

KERIM: Yeah.

MICHAEL: Amazing.

How full do you think this place could have been of water

when it was in use?

So the levels of the hydraulic plaster here might indicate

the maximum storage level for us.

MICHAEL: So, I mean, this place could have been absolutely full of water

right to the top?

KERIM: It is possible, yes, and probably connected with the water supply lines

of the city.

This was one of the large cisterns of Constantinople.

- This was one of the largest? - Yeah.

Actually we have...more than 200 cisterns identified.

These water tanks came in all shapes and sizes.

Tiny ones for single families, and massive ones like this for whole neighbourhoods.

MICHAEL: And so where would the water here have been going?

KERIM: This area was the Great Palace of Constantinople.

So this was used by the Great Palace.

We can keep going till that wall, till it blocks our way.

So we cannot continue any further. But the cistern continues that way.

MICHAEL: Oh, I see. So the wall goes halfway up,

but actually this chamber continues around on the...

- KERIM: It continues, yes. - MICHAEL: ...on the other side.

So, Kerim, what's this channel here going curving off to the right?

KERIM: This might indicate

the connection between an Ottoman fountain built in front of the façade.

So, it was built in the 16th century.

Then we can say that the cistern stayed in use

at least for 1,000 years after the sixth century.

So it's converted in... The Hippodrome's been here since,

well, since the first centuries AD in different forms,

converted into a cistern in the sixth century...

Yes.

...and still being used as a cistern at least in the 16th century?

Exactly. Yes.

A thousand years here of water just kind of around us.

So it's also proves the continuous needs of stored water in the city.

Thank you. Thank you for showing it to me.

You're very welcome, Michael.

Let's go back.

As the scan team goes to work inside the Hippodrome,

Tom also finds it hard going.

TOM: We're obviously carrying some extremely expensive equipment.

The last thing we wanted to do was fall into that stagnant water

that's clearly stood there for years.

You do kind of worry about what wildlife could be under your feet.

Rats. Dead birds. Guano all over everything.

MICHAEL: Our scans show how a structure built for entertainment was transformed

into a life-saving reservoir.

Now it's largely forgotten...

...except by those who know invisible Istanbul.

With a rapidly growing population, improvised water storage wasn't enough.

Constantinople used Roman engineering genius

on an even grander scale.

There's no better place from which to witness the miracle

of Roman hydraulic engineering than right here, having a cup of tea -

because I am surrounded by an aqueduct.

This is the Valens Aqueduct,

the major route bringing fresh drinking water into the city.

The Romans needed their aqueducts to be as straight and as efficient as possible

and that meant conquering the very landscape.

Here we're between two hills,

and the Roman solution is to build a bridge between them.

So, this thing goes 30 metres up into the air

and over a kilometre across from one hill to the other.

And as a result,

even the modern metropolis of Istanbul has to bend around it.

Hi, Jim. How are you doing?

The man to tell us about it is Professor James Crow from Edinburgh University.

MICHAEL: Farther than it looks from down the bottom, actually!

JIM: Yes. It's wonderful when you get up here, don't worry.

Jim's been mapping the ancient city's water supply system for decades.

MICHAEL: Thank you very much!

Oh, what a view already! And the sun! (LAUGHS)

JIM: Welcome to...

MICHAEL: I might leave my jacket here. This is...fabulous. What a place!

JIM: Yep.

Jim, I feel like I'm flying above the streets below us.

But this is the aqueduct. Where was the water going?

Well, within this, there are big channels.

They are nearly as tall as you, as wide as that,

and they carry the water from huge distances to the west of the city,

into the city to fill its cisterns and its fountains.

So, Jim, how have you discovered this network?

Well, before we started, we knew there was this very long system outside of the city

but it was over 20 years of fieldwork,

looking at old maps, a whole range of things, and then

talking to lots of people in villages, having lots of cups of tea,

finding out where these structures are and the channels are,

because it's a deeply forested area - it's like working in a jungle almost.

And suddenly these great bridges

will appear out in deep-sided valleys covered in trees.

I've got an image of Indiana Jones already!

Well, I don't know.

It was quite fun to do. But at the same time, we were then able to map the system,

project the whole length and assess how long this system extends

into the countryside and away from the city.

And are we thinking about a water system here

as sophisticated as that of Rome?

Certainly as sophisticated. And in some ways it surpassed Rome

in terms of the engineering skills that were needed.

And engineers, modern engineers,

when we talk to them about it, are just astonished.

They cannot understand how these guys were capable of it.

Our scans help show how the water flowed through two great channels

inside the aqueduct bridge.

The water went into 209 cisterns across the city.

Some improvised, like the one in the Hippodrome,

some purpose-built

and some as big as a football pitch.

They were fed by two aqueducts coming from forest springs

up to 200 kilometres away.

With over 580 kilometres of channels,

this was the longest and most sophisticated water system

of the Roman world.

It helped transform Constantinople

into one of the richest cities in the world.

But such a wealthy and strategically important city

was vulnerable to attack.

The Romans surrounded the city with walls

that were said to be impenetrable.

Attila the Hun, Arabs, Bulgars, Russians all met these walls

in their attempts to lay siege to the city of Constantinople.

Enemies attacking by land faced a moat,

a wall,

a no-man's-land

and then a second wall - 15 feet thick and 40 feet high.

The land walls alone stretch nearly four miles across the peninsula,

with nine massive gates and 96 towers like these.

They completed a ring of stone

from the harbour inlet, known as the Golden Horn, to the sea.

No-one managed to break through these walls for centuries.

In fact, their most dangerous opponent over the centuries

were the earthquakes that this area is prone to.

Earthquakes damaged these walls time and again,

and time and again the citizens came back

to rebuild them bigger, better and stronger than ever before.

But nothing lasts forever.

So far, our scans have recorded ruins that tell the story

of the rise of Constantinople.

The ruins of the once-glorious Palace of Boukoleon also record its decline.

This was once a chapel

and it's now, according to the signs on the walls, the home of Hasan,

who's decorated it. Well...

...it's kind of like my daughter would decorate it, really.

It's a home...of sorts.

This palace was destroyed

when Christians turned on one another.

There'd been religious disputes between the Roman Catholic world

and the Byzantine Empire for hundreds of years.

And in the end, Western crusaders found Constantinople's riches

just too much of a temptation.

This palace was damaged and rebuilt many times in its history.

But its final death knell was in 1204

when Western, European crusaders led by the city of Venice

came here and destroyed the city

and took this beautiful place down with them.

The Western invaders stayed in Constantinople for over 50 years.

They desecrated Eastern Orthodox churches,

destroyed the ancient library

and looted the Great Palace complex, leaving them in ruins.

The clash between the Eastern and Western wings of Christianity

tore Constantinople apart.

By the 15th century, Constantinople's population

was no more than 70,000 people.

Its power, its glory days were behind it. It was a shell.

And it would only get worse.

By 1452, the city of Constantinople

was all that was left of the Eastern Roman Empire.

It was a tiny Christian island

surrounded by the Muslim Turks' Ottoman Empire.

The Turks had the city at their mercy.

Constantinople had to find ways to survive alone.

Packed with cisterns and with good agricultural land within the walls,

the citizens of Constantinople were well prepared for any siege,

and it's a tradition that still continues today

with the gardens here around me that are using

the old moat and even the space in between the city walls

to cultivate their fruit and veg.

But while the people of Constantinople grew their own food

and rationed their precious water,

the Ottoman Empire was tightening its grip.

With the city surrounded, supplies could only enter by ship.

The Turkish leader Sultan Mehmet built this fortress to stop them.

It guarded the narrowest point on the Bosphorus,

less than 800 metres from his fort on the Asian side.

Today, this place is known as Rumelihisarı,

which means "the fortress of the Romans",

because we're on the European side,

and when Mehmet came and built this fortress, this was Roman land.

But its original name is Bogazkesen.

Now, that means "the cutter of the Bogaz" - the Bosphorus, the river.

But, in Turkish, the same word means "throat".

This place was intended to cut the throat - of the Bosphorus

and of the people of the city of Constantinople.

The main tower of Rumelihisarı fortress

was a strategic command post for Mehmet's whole operation.

Its secrets are locked away,

but local historian Ali Zirek is taking us to see them.

- Amazing. Do you have the key? - Yes.

I'm really curious to find out what this tower was used for

and Ali's taking me up to the top to find out.

(LAUGHS) What a room! What a space, Ali!

What went on here? Do we know?

So we're in a place where Mehmet may have conceived his final plans

for taking Constantinople?

There's the heavy smell and weight of history in this room.

It's extraordinary.

Our scans allow us to really get under the skin of Mehmet's HQ.

As we rise through the tower's seven storeys,

a war machine of ruthless efficiency is revealed.

With walls up to seven metres thick

that protect Mehmet's council chamber.

Crenellated lookout positions.

Arrow slits and firing positions.

Toilets.

Grain storage.

Living quarters for up to 400 soldiers.

Armouries bristling with their weapons.

A chute to drop boiling oil onto an invader at the front door.

And an unrivalled view to guard the narrowest part of the Bosphorus.

The tower also holds an ancient remnant of Constantinople's defence.

What is this?

Was this...?

Was this the chain across the...?

For the Golden Horn?

- ALI: Yes. - MICHAEL: The Golden Horn chain?

Wow!

My God, it's still so solid.

That's incredibly heavy.

No wonder it worked so well for so long.

This iron chain is the stuff of legend.

For centuries, the chain was stretched across the inlet known as the Golden Horn

in times of danger.

Now, it stopped Mehmet's ships from reaching the heart of the city.

But...

Mehmet had a genius solution.

He ordered logs greased in olive oil

to be laid across the landscape in a road

that would allow his ships to be dragged across into the estuary,

thus getting around the great chain.

And on 22nd April, 1453, Mehmet's fleet made its way across

to take up position to besiege the city of Constantinople.

The Byzantine Christian forces were down to around 5,000

against an Ottoman army of 200,000.

The women, children, old and sick

took refuge behind the great doors of the Hagia Sophia.

For 53 days, Mehmet bombarded the city

with some of the most advanced artillery in the world.

On the 29th of May, 1453,

the legendary walls of Constantinople were finally breached.

The invading army closed in on the Hagia Sophia.

They smashed down the doors.

The cowering Christians were raped, slaughtered and enslaved.

(SCREAMING AND SHOUTING)

Mehmet himself lamented the devastation.

"What a city we have given over to plunder and destruction."

The final metamorphosis of the Roman Empire -

the Byzantine world -

died less than 50 years before Columbus discovered America.

And, for the city of Constantinople, a whole new chapter in its history.

No longer Constantinople, it was now known as Istanbul -

an Islamic city, capital of Mehmet's Ottoman Empire.

The East now held sway.

The best place to see how the city changed is back at the Hagia Sophia.

The cathedral became a mosque.

Over time, minarets were added on each corner.

And these enormous panels were erected to spell out the name of Allah,

the Prophet Muhammad and his grandsons.

There were more subtle changes, too -

these mosaic crosses were concealed by Islamic decoration.

But this was by far a more important change.

This was the mihrab,

and it sits off-centre to the apse behind it for a very good reason,

because it points in the direction of Mecca,

and thus gives the direction in which the Muslim faithful should pray.

Now an integral part of the Muslim world, the whole city was reborn.

Sultan Mehmet is still known as Fatih - the Conqueror -

but he was also a builder.

Mehmet rebuilt the city walls,

repaired its water supply and kick-started the city's economy

by establishing this place, the Grand Bazaar.

Mmm. OK, it's not too bad.

New people and new cultures poured into the city.

Too strong for you? (LAUGHS)

Istanbul was now the capital of the Ottoman Empire.

...turns into that. But I'm going to have a look around,

and I'll come back. Thank you very much.

My favourite place in the Grand Bazaar?

The barber's.

People often ask,

"What was the impact of Mehmet's victory on the city of Constantinople?"

And historians call it the worst destruction in the history of mankind.

But, at the same time,

this was the beginning of a new chapter for Constantinople,

a chapter in which the city was going to be bigger and better than ever before.

Istanbul was transformed into the bustling, energetic place

it is today, full of Asian and European influences and tastes.

Now this is balik ekmek.

It's a fried fish sandwich,

and it's the thing to eat down here at Eminönü, near Galata Bridge.

And, for my money, there's no better place in Istanbul than here

to feel the swirling mix of cultures that defines this city,

that jostles strongly,

sometimes as roughly as the waters that run through the heart of the city.

As they developed the city further,

the Ottoman Turks drew on the learning of both East and West.

Our 3D map shows us one of the greatest Ottoman design innovations -

a new mosque to outdo the Hagia Sophia.

The Süleymaniye Mosque.

Built for Sultan Suleiman the Magnificent in 1557,

it remains an island of peace to this day.

People come to mosques obviously to pray, but...

...it's also about getting away from the hustle and bustle of the world.

And there's something also I absolutely love about this kind of place.

It brings together not just people going in to pray,

but the whole community.

Kids are running around, playing with their families,

friends are catching up to have a walk and talk.

This is a place to get a little respite and energy for the soul.

The genius of the Süleymaniye Mosque is found in its grand design

and in its smallest detail.

Much is invisible, but not to my guide, architectural historian Olcay Aydemir.

Oh, what a door! What an amazing...

Oh! Olcay, this is incredible. What a space!

- I-I feel that. - Yes, yes.

I feel that you want to move towards the centre of the space, don't you?

It's extraordinary.

The sense of...

...of-of...just volume and-and, er... light in here is just incredible.

And, Olcay, I've noticed that all of the lighting in here

is very low compared to the ceiling.

So, why? Is there a reason for that?

So, it's designed to make us again feel more comfortable here.

- And I keep seeing shells. - Yes.

Ostrich eggshells?

Are they just a decoration?

- Ostrich shells drive away spiders? - Yes, yes.

Brilliant! Now that is a tip for us all at home, right?

Everyone needs an ostrich shell in their house.

- And it's all electric now... - Yes.

...but when the mosque was built, this would have been candles?

So we have to imagine, what, thousands of glittering lights,

keeping this place alight.

And the other thing I was thinking - if there were candles and oil lamps,

there must've been lots of soot produced,

and the ceiling must have been black with soot.

And yet the walls and ceiling are pristine.

It takes our scans to reveal the mosque's ingenious solution -

a ventilation system hidden in the walls.

The soot from the lamps was drawn up

through concealed funnels into a secret room,

where it stuck to the walls,

and was made into ink for sacred manuscripts.

Today, only graffiti remains.

Another design secret lies under our feet.

OLCAY: Ah, strong.

MICHAEL: Wow!

- What are these tunnels? - Channels.

These tunnels keep the building well aired today,

but they originally brought drinking water to the workers building the mosque.

Ingenuity is everywhere.

Here decoration doubles as sound baffling,

so that everyone can hear the sermon clearly.

The Ottomans matched the grandeur of the Hagia Sophia,

and took its design and technology to a whole new level.

Sultan Suleiman had great ambitions for the people of Istanbul.

He created a complex around the mosque

to house a hospital, six schools, Turkish baths,

a travellers' inn, a bakery, and a medical college.

His goal was to make the mosque

the centre of the city's flourishing society.

An important part of the mosque complex is the imaret, or public kitchen.

It fed over 1,000 of the city's poor every day,

through this tiny hole in the wall.

Brilliant. What a brilliant system.

So, it's a blind transfer - I don't see them, they don't see me.

Everyone is equal.

And can I pick it up?

How ingenious.

This was a Sultan's mosque meant for everyone.

Suleiman's kitchen was designed to feed Muslims, Christians and Jews alike.

Today, it's a commercial restaurant.

I've seen so many aspects of ancient Istanbul

hidden beneath the surface of the city.

Now, I'm going to experience it through virtual reality.

- It's all green. - It is all green, yeah.

I recognise these. So, this is the one-way ticket to Istanbul, huh?

MATT: This is your helicopter. In you go.

Wow! Hello, Istanbul!

Here we go.

MICHAEL: So this is the view you were getting

when you were up in the helicopter?

MATT: Exactly. So if we start, the Hippodrome...

MICHAEL: Ah, the back end here, isn't it?

And there's where we went into the cistern.

There's the staircase.

And, wow, there we are with all that mucky, dirty, rat-filled water.

MATT: And then... Then we stride across and...

MICHAEL: And then... Oh, I recognise down here. This is...

- There she is. - There she is. Hagia Sophia.

And you can see the clear differences between the minarets,

all constructed at different times, and then...

(LAUGHS) ...I can hold the dome of Hagia Sophia in my hands.

- (MICHAEL LAUGHS) - MATT: In we come.

This is a perspective that you'll probably be

- a little more familiar with, actually. - I am.

And one of the wonderful things we can do here, of course, is start to rise up.

So...

What? Whoa, whoa, whoa, whoa, whoa!

We're flying through the air!

The detail of the roof - it's beautiful.

Oh, my Lord. Here comes the roof.

Oh, whoa. OK. Slow, slow down.

- MATT: You'll be fine. - We're getting really...

Whoa, whoa, whoa, whoa, whoa, whoa, whoa!

MATT: So here we are.

MICHAEL: And there... Oh, my God.

We're on the top of the dome.

MATT: You are standing on the millimetre-thick skin of the top.

- You can just walk... (LAUGHS) - Yeah.

I-I feel like I want to walk really gingerly...

- Yeah, yeah. Exactly. - ...just in case I fall back through.

MATT: And there may be some sort of edge anywhere.

MICHAEL: And there... God, you can see the lumps and the bumps right there.

- There's a massive lump. - Yeah.

What? Oh, there we go!

You've sent me flying through the air again...

The Hagia Sophia is like this whole city -

it's been bashed about, but it's always found a way to survive.

MATT: ...our journey back down to ground level.

MICHAEL: This is extraordinary.

Hello.

Istanbul has endured by adapting buildings like the Hippodrome

to stay alive through droughts and war...

...and kept fresh water flowing to everyone through its elegant aqueducts.

This is a city built upon layer after layer of history and culture.

And the people of Istanbul have fought armies and earthquakes

to preserve their home, against all the odds.

Istanbul is a city that's been conquered, destroyed and rebuilt

by both East and West.

And, as a result, in both its past and its present,

it's a uniquely cosmopolitan melting pot of cultures.

My hope for the future is that,

whatever grand shifts in power between East and West there may be,

Istanbul is allowed to keep its unique personality.