♪♪ -I'm Darius Arya, and I'm an archaeologist going in search of the ancient world in three of the most exciting cities on Earth -- Athens, the birthplace of democracy; Istanbul, the crossroads between Europe and Asia; and in this program, the gateway to Ancient Egypt, Cairo.

♪♪ The skyline of Cairo is full of extraordinary historic buildings.

But so much of Cairo's past remains invisible.

I'm going to be exploring its hidden spaces buried deep beneath ancient monuments and underneath the modern streets.

It's not easy getting down here.

I'll be working with a 3-D scanning team who are using laser technology to reveal the secrets of Cairo's fascinating past.

♪♪ But the history of Cairo is not all about Ancient Egyptians.

I specialize in Roman history, so I'm thrilled to discover a Roman fortress.

Really impressive.

I explore the magnificent Arabic Citadel.

Wow.

Oh, man!

Okay, that's a drop.

That's a drop.

-It is.

-And I'll be using virtual reality to investigate the ancient world in a whole-new way.

♪♪ Welcome to "Invisible Cairo."

♪♪ ♪♪ -The River Nile -- The life force that flows right through the center of Cairo.

The world's longest river, it springs up in the African Great Lakes over 4,000 miles to the south.

It truly is a natural wonder.

♪♪ For millennia, the Nile flooded every year and transformed arid desert into fertile fields.

Cairo is at the point where the river splits up into the Nile Delta to make full use of the river's bounty, and that's why the same location was so sacred and important to the people of Ancient Egypt.

♪♪ [ Horns honking ] ♪♪ The region that's now Cairo has been ruled by many empires, but one iconic shape, built by the very first civilization, defines the city's skyline.

The Great Pyramid is the last remaining wonder of the ancient world.

♪♪ It is so fantastic to be in front of the Great Pyramid.

I mean, it's an image that you know, it's so famous, but to be here in front of it, to look at that structure, its mass, it is awe-inspiring.

But all of this is not a city.

It's a cemetery of the kings and queens of Ancient Egypt -- the grandest cemetery of the whole world.

♪♪ The Great Pyramid of Giza was built over 4,500 years ago, around 2560 B.C.

20,000 workers built it, but it was the last resting place for just one man, a pharaoh called Khufu.

Our scanning project, one of the most detailed ever carried out in Cairo, begins here, and the team is led by Will Trossell.

They're going to create a 3-D computer model of the pyramid to help reveal the secrets of its design -- new research to add to existing knowledge.

You guys have done a lot of projects, but here we are, looking at one of the wonders of the world.

I mean, it's massive.

What are the challenges in this project?

-Well, the major one is the temperature.

We've got scale, and we've got accuracy, as well.

There's three big things there.

-I'm with you about the heat.

I mean, it's just -- It's beautiful to be here in the sun, but what kind of effect is it having on the measurements?

-Just the heat from the sun creates a lot of noise in our data, so we don't want to be getting erroneous measurements of the top of the pyramid.

We want to make sure it's very accurate.

-And at the same time, you're not going to be here for months doing this work.

-There's a lot of pressure on the team to make sure it all comes together as a really tight model so that we can check how accurate they were being when they built the pyramids.

-So it's you guys against the Ancient Egyptians?

-Ah, yeah.

[ Laughs ] See who wins.

-Good luck, man.

All right.

I'll see you.

-Thank you.

-All right.

Ciao.

It's certainly a challenge.

At 450 feet tall and made out of 2.3 million stone blocks, the Great Pyramid is still the heaviest building in the world.

I'm going in at the robbers' entrance, where thieves dug a tunnel into the pyramid to steal any treasure inside.

This is going to be good.

This is amazing.

Been here once before, but I've never had the opportunity to explore it.

Let's go.

♪♪ ♪♪ Much of the Great Pyramid is closed off to the public.

But we've been granted special permission to enter a mysterious chamber deep below ground level.

It's not easy getting down here, but what I'm really thinking about is, who carved this?

What conditions were they in to go through the bedrock with nothing more than a pickax and a torch or a lamp?

And let's see where this leads.

♪♪ Ah.

I've gone down a shaft a couple hundred feet, and then I had to go through a crawlspace about 30 feet long where I could barely fit into this...

I think it's a chamber.

You can still see the tool marks.

I'm well beneath the pyramid.

I don't know if it's unfinished, but there's definitely something going on right over here, and it's a big mystery, what really was taking place in this chamber.

Some Egyptologists believe this subterranean chamber was built to be the burial tomb but then abandoned.

There's something over here, too.

Looks like it's a dead end.

Going to have to turn around.

I'm hoping our scans will help make sense of this place.

It's incredibly hard to grasp the layout of the pyramid.

But first, I'm heading up into the heart of the pyramid to meet Egyptian archaeologist Zahi Hawass in the ceremonial passageway known as the Grand Gallery.

Hey there.

-Hi.

-Zahi, how are you doing?

-How are you?

-Nice to see you.

-Nice to see you.

-Bit of a hike here.

This is an amazing space.

-You have to imagine how the Egyptian will construct an amazing, grand gallery like this, because this is the entrance of the palace of the king.

-The gallery is 28 feet high and 153 feet long, and leads up to the king's tomb.

-Now I take you to the burial chamber.

-All right.

Not an easy space to get through.

The burial chamber is high up in the pyramid.

Oh, here we are.

Wow.

And in this room, Pharaoh Khufu was laid to rest.

-Magic.

What do you feel?

-This is -- It's almost electric, just being in all this history.

-Electric means more than magic, yes?

-[ Laughs ] -Everything here built of granite.

-This tomb is now almost empty, any treasures stolen by grave robbers just a few centuries after it was built.

Only the sarcophagus that once held the mummified body of Khufu is left.

So, tell me about Khufu.

When he died, what happened then?

-They take him to workshop where they mummify the body.

After they mummify the body, they bring him through the entrance, and they bury him here.

-But that whole process of bringing the body here, that must have been one heck of a ceremony.

-It is.

It took 70 days.

-This tomb within the pyramid, what did it mean to the people of Egypt?

-It is the palace for the afterlife, and therefore, the king became God, and he lives in his palace for immortality.

-The first scans of the Great Pyramid are in, and I'm hoping they'll make sense of its layout and reveal the precision with which it was built.

-Hey.

-Hey, Will.

How you doing?

-Darius, good to see you.

-Nice to see you.

What have we got here?

-Well, something quite incredible, really.

So, we've stitched all the scans together from the inside and the outside, so we've got this now-complete millimeter-perfect, detailed model of the entire pyramid.

-Unbelievable, unbelievable.

-So, yeah, let me show you around.

-Yeah, want to relive the glory.

♪♪ Ooh, fantastic.

Now, that's something we didn't experience, because we were going through all these corridors and crawlspaces and chambers, but you had no idea where even you were in the pyramid, and this way, we see it.

-This is really interesting over here.

So, here, you can see the robbers' tunnel and compare that to the run next to it, which is the original descending passageway down to that subterranean room.

You can see the contrast between the two -- one by the robbers, kind of like a big root of ginger as they kind of quarry their way into the pyramid.

-They're tomb robbers.

I don't advocate that sort of stuff, of course, but look at the guts that it took to do what they did.

I mean, that's kind of mind-boggling, to think that they're going to just hack away and remove those blocks to get to the goods.

But, man, it's ugly, but it worked, and that's how we got into the pyramids.

The perfectly-aligned descending passage leads down to the subterranean chamber.

There's a lot of effort going to construct that shaft.

I mean, that's no joke.

I mean, going through that's intentional, and it bottomed out to this chamber.

-Mm-hmm.

-What was it used for?

-Complete mystery.

-Yeah.

-It has a very curious shape and form.

♪♪ -Whatever the purpose of the subterranean chamber, we do know the more polished king's chamber higher up was the burial place for the pharaoh.

-This beautiful, incredibly clean, incredibly powerful room -- what an amazing piece of architecture inside the pyramid.

♪♪ -And, of course, it was only for the pharaoh, so this is something -- We're really privileged to be able to see it now in this virtual space.

I mean, who was going to see that in the time of the Ancient Egyptians?

Basically nobody.

-Hmm.

-The scans allow us to visualize new aspects of this remarkable structure.

Will has inserted this red band around the base of the pyramid to measure how level it is.

Despite being hundreds of feet apart, the four corners are at the same height, within just four inches of one another.

It's confirmed the pyramid is almost exactly level.

It's not just something done on the fly.

I mean, this is incredible.

Yeah, this is great engineering.

-You can see that the pharaoh really did appreciate the design.

The simplicity masks mountains of engineering and ingenuity that went into that to build this, so I think he was clearly a guy who appreciated design and architecture and engineering.

-Yeah.

It's fantastic to see how the scans have confirmed the precision with which the pyramids have been built -- this in a time when the rest of the world was basically living in mud huts.

Even today, in the 21st century, you don't have architecture that's always this precise, and this is a great testament to the greatness of the architects, the engineers, the builders, the stonecutters, the masons of Ancient Egypt.

This is their legacy.

To learn more about this advanced ancient culture, we're now going to use our scanning technology to investigate the most famous sculpture in the world.

♪♪ The scale of the Sphinx is colossal.

It's a monumental figure, over 200 feet long, over 60 feet high.

And what is it?

Well, it's got the body of a reclining lion and the head of a man.

But whose face is it?

The Sphinx sits at the foot of a ceremonial road leading up to the second middle pyramid of Giza, close to the Great Pyramid.

This was built for another pharaoh, Khafre, and he was the son of Khufu, buried next door.

The Sphinx was traditionally believed to represent Khafre, a spectacular gesture of self-promotion, but in 2003, some researchers came to the conclusion that Khafre had instead built it to honor his father, Khufu.

♪♪ Using our laser technology, we'll scan the face of the Sphinx and compare it with the scans of sculptures of Khafre and Khufu.

In this way, we might answer the age-old mystery of who the Sphinx really is.

[ Horns honking ] The Great Pyramid at Giza wasn't the first to be built.

Researchers now know more about the fascinating origins of pyramid construction, and the breakthrough was made in an important location 12 miles away, south of the city.

We're driving across the vast urban landscape of sprawling Cairo, but we're actually making an ancient journey from the cemeteries of Giza to the ancient capital, Memphis.

♪♪ The pharaohs of Egypt's Old Kingdom ruled from the city of Memphis.

Its population of 30,000 people might not sound like a lot, but at the time, Memphis was one of the largest cities in the world.

This was once a cosmopolitan city filled with temples, palaces, and settlements, but it's really hard to get a sense of that city today.

We can turn instead to this colossal statue of Ramses II that was found in the city.

It once stood over 30 feet high, one of a pair that stood in front of a temple, and it gives us a sense of how magnificent this city once was.

♪♪ Made mostly of mud bricks, Memphis has crumbled away to dust, but just two miles away, the Ancient Egyptians built something that would endure -- the stepped pyramid of Saqqara.

It was completed in 2650 B.C., 80 years before the Great Pyramid of Giza -- the earliest large-scale cut-stone construction anywhere in the world.

To find out more about this prototype pyramid, I'm meeting Egyptologist Yasmin El Shazly.

-It's historically very important because it marks the transition from mud-brick architecture to large-scale stone architecture.

-Well, I'm looking at it right now,, and still today, it's very massive.

-Before they built this one, kings were buried in mastaba tombs, which are basically flat platforms.

-So, kind of like the first level of this?

-Yes.

-What's the thinking to actually go in that direction, to go up?

-Some say that it acted like a stairway to heaven, because the soul of the king was believed to unite with the northern stars.

And another theory is that it was built to be a huge monument to be seen from the capital, Memphis.

-"I'm larger than life, and in death, you know, I'm literally above everybody else."

-Exactly.

♪♪ -My God, this is really walking back in time.

-Yes, it's amazing.

-It's like out of a movie set, except for it's real.

-[ Laughing ] Yes.

-We've been granted special access to explore the very first pyramid.

In this way, we'll find out how it influenced the design of all the later pyramids.

Oh, this place is all shored up here.

This must be some project.

-Well, it's closed to the public for restoration, so you're very lucky.

But be very careful.

Stick to the right here because there's a hole.

-Yeah, I'll do that, definitely.

Ah, wow.

It really opens up now.

-Yes, look at that.

-That is impressive.

So, in this point, are we looking at the center of the pyramid?

-Yes, and it's...

This shaft is 28 meters deep.

-Wow.

That's like 100 feet.

So, at the bottom of that is where the king is buried?

-Yes.

-Wow!

Can we go down this way or...?

-No, no, no.

It's dangerous to go down this way.

We will go the other way around.

-All right.

Lead the way.

-Yes.

Please follow me.

-As we explore ever deeper, the interior becomes a confusing maze of tunnels, corridors, shafts, and chambers.

-Watch your head -- and your back.

-Okay, yeah.

Wow, it is tight down here.

This place is like a labyrinth.

-Yes, it is, definitely.

-These guys could've made it a little bit bigger.

Yasmin is taking me to a small antechamber that tells us more about why the first pyramid was built.

-Look at that.

-Ah, wow.

So, a little bit of the decoration is still here.

-Yes.

These are blue faience tiles.

All these chambers were covered in them.

Unfortunately, most of them are gone.

-Mm-hmm.

-But you can imagine what it was like when it was first built.

-Yeah, I mean, I can see row after row of just how they were inset and so forth.

-It's really just great to have this much to re-create everything that was once here.

-Yes, it would've been incredible.

-So, what is the purpose, then, of this kind of decoration?

What -- How would it fit?

-It was actually designed to look like the king's palace.

-Okay.

-Because, to the Ancient Egyptians, the tomb was actually the house of eternity.

-Mm-hmm.

The first pyramid was built to conceal a palace for the afterlife, and it was all for King Djoser, a pharaoh who ruled over the newly unified kingdoms of Upper and Lower Egypt nearly 4,700 years ago.

-We don't know a lot about him, but what we do know is that he was a powerful king who led successful military campaigns, and he was definitely a very powerful king, because he was able to mobilize large numbers of workmen to build this pyramid.

This was a national project.

-Right, and you're going to have something which is going to make a big statement to everyone forever that, "Look what we were able to build."

This is his eternal home, then.

-Yes.

♪♪ -Will and his team are already at work.

Our 3-D model will help us understand the design of the Saqqara pyramid, revealing clues about how it went on to inspire the Great Pyramid.

♪♪ While they scan, I'm at the Egyptian Museum in the center of Cairo to find out more about King Djoser.

♪♪ But first, I can't resist a visit to the most beautiful archaeological object of Ancient Egypt.

♪♪ ♪♪ This is the death mask of Tutankhamun.

It was found over his mummified head.

And this is just part of a vast treasure of the pharaoh.

The head alone here weighs 22 pounds of gold and precious stones -- obsidian, lapis lazuli, faience.

It is extraordinary, and when you think of Ancient Egypt, you think of this image.

♪♪ Tutankhamun became pharaoh at the age of 9.

He died about 10 years later.

But during his short reign, he restored religious tradition and brought order to a country in turmoil.

♪♪ But all this was happening many centuries after the building of the first pyramid.

And now what I've really come to see -- a unique object discovered at the stepped pyramid.

The only sculpture we have of that pyramid pioneer, King Djoser.

He's not as bling as Tutankhamun, but he's 1,000 years older and something very special.

This statue is the earliest life-size statue of a human being ever, and you can just see how magnificent it is and once was.

It has traces of paint -- the mustache, the beard.

His eyes were inlaid with precious stones.

So, not only were the Egyptians pioneers in architecture, they were pioneers in art.

♪♪ The Cairo Museum also contains a full wall of those blue tiles we saw in the step pyramid of Djoser.

If you look closely, the design here on the wall was meant to represent rush mats that would've once decorated the walls of the palace of the pharaoh.

But in the afterlife, it becomes something so sumptuous and a very rich material.

It underlines the fact that they invested so much more in the afterlife than they did in life.

♪♪ In addition to all the preparations for the afterlife, King Djoser also had to demonstrate his right to reign during his lifetime.

♪♪ If a pharaoh's reign lasted 30 years, he celebrated with a ritual called Heb Sed, and that meant running around a large arena like this, and afterwards, he had to have a wrestling match.

Now, the thing is, Djoser's dead, and that's his pyramid.

This arena is next door because it's saying, what he did in life, he's going to continue in death for all eternity.

The construction of the first-ever pyramid was a feat of ancient innovation, and our scans reveal it was a fascinating learning process.

♪♪ The six well-defined steps of the structure stand out clearly, but at the bottom layer, you can just make out a join between two sections.

Tease this apart, and you find a much smaller structure known as a mastaba tomb hidden inside.

This was built first.

But at some point during construction, the flat mastaba was expanded into the full six-story pyramid, a pioneering process of innovation.

♪♪ Our scan reveals the whole of the interior is deep below ground level, including the huge central shaft leading down to the burial chamber.

It's all very different from anything at the more streamlined Great Pyramid.

Right next to the base of the burial shaft is the small antechamber with the beautiful blue tiles.

♪♪ And out from the shaft is a labyrinth of tunnels going off in all different directions.

♪♪ It's estimated that there are over three miles of tunnels.

We were only able to scan a few of them.

♪♪ The step pyramid of Saqqara ushered in a new age of monument building, but today, we look at it as more like a prototype because, just 80 years later, the Egyptian engineers and architects refined their skills to build a much more ambitious project, and that was the Great Pyramid in Giza.

Building the Great Pyramid was a massive undertaking lasting about 20 years.

Until recently, little was known about the workers who built it.

It's long been assumed the majority were slaves.

Then, in 1990, these tombs were found completely buried in the sand just next to the pyramids.

Zahi Hawass suspected they might belong to some of the builders of the pyramids.

Nothing I like more than seeing an excavation site with the person who actually did the excavating.

-Yes, I found this tomb.

It's for an artist.

His name is Petety.

-Mm-hmm.

-And, actually, he was afraid that his tomb will be completely robbed, and he left a curse inscription.

-Very nice.

-And if you look at this curse inscription, he's saying at the beginning here, "I never did anything wrong in my life."

Of course, he's a big liar.

And he said again, "If anyone will touch my tomb, he will be eaten by..." -Ooh.

Wow.

-"...crocodile, the hippo, and the lion."

-Unbelievable.

What a horrible way to go.

-It's amazing.

He was afraid that his tomb will be stolen, and it's why he left inscription.

On the other side, the beautiful scene of his wife, and look -- She's almost equal to him, and this is very rare.

In Ancient Egypt, always, the woman is in a smaller scale beside the husband, but it seems to me that this could be love, or she was a powerful woman, that she gave an order to him, and the profile is really show an excellent artwork.

-So, do you think that this kind of portrait, too, was something that was idealized or realistic features?

-This is idealistic.

This is what they want to be shown in the afterlife.

Then an ugly lady could show her beauty for the afterlife.

And this to show that not only kings and queens can do that, but also poor people can go to paradise.

-And be buried together for all eternity.

-Exactly.

-Thanks to the excavations like Zahi's, we now know that the people who built the pyramids were not slaves but free men.

And carvings on the walls of the tombs show how the 20,000-strong workforce was kept going.

Bakers who made the bread.

Brewers of the all-important beer.

Sculptures from their tombs show us more clearly what they looked like.

This is Inty-shedu, carpenter who made the boats that carried the stone blocks for constructing the pyramids.

♪♪ Much of what we think about in Ancient Egypt is pyramids and the pharaohs and their lives, but here in this cemetery, we have insight into the lives of the average Egyptian -- the mason, the artist, the people that were basically the fabric of society -- and it gave me a much more intimate view of what it was like to live in Ancient Egypt.

Earlier, we scanned the Sphinx to try to solve the mystery of which pharaoh it really represents.

The two candidates were Khafre or his father, Khufu.

♪♪ Now we're returning to the Cairo Museum to scan the faces of their sculptures.

This is Pharaoh Khafre, the son of Khufu, and here he is out of this incredibly beautiful stone called diorite.

And what you have is a very symmetrical pose, except for this one clenched fist.

Behind him is actually the falcon, Horus, protecting his head.

He is seated here regally for all of eternity.

This is Khufu, his father, and this statue of him is only three inches tall.

Now, we know it's a representation of Khufu because his name is on the front.

It's striking that this tiny statue is the only representation we have of the pharaoh who built the greatest and largest pyramid of all.

♪♪ By scanning the faces of the pharaohs, we'll be able to compare them with that of the Sphinx.

For the scans, the team need two technologies.

-So, we've got the laser scan, which is maybe five mil of accuracy, and the photogrammetry, which will take us much closer to one, really pull out the detail here in the face so we can kind of really zoom in.

-And what do you think between Khufu and Khafre?

I mean, this is going to hopefully resolve the riddle of whose face is on the Sphinx, right?

-Oh, I'd love to unlock that riddle, yeah, yeah.

♪♪ -This is the scan of Khafre.

The face of the Sphinx is superimposed on top, scaled to the exact same size.

We ignore the nose, missing from the Sphinx.

The blue and red areas show points where the faces are most different, the greens and yellows a closer match.

And this is the scan of Khufu, the father, with the Sphinx's face overlaid accurate to nearly .001 inch.

♪♪ By comparing the two, we can see there's slightly more green and yellow on Khafre's scan, especially along his cheeks and chin.

It's a closer match.

♪♪ It's not definitive, but our results support those who believe the Sphinx is Khafre, the son, rather than Khufu.

This suggests Khafre built the Sphinx not to honor his father... ♪♪ ...but to boost his own ego for eternity.

♪♪ When the Sphinx and pyramids were being built here, the course of the Nile flowed much closer to Giza, and harbors allowed boats to unload stone blocks from all across the country.

But over the two millennia of the Ancient Egyptian civilization, the Nile constantly changed its course.

♪♪ But many things remain consistent.

All the capitals were always located along the life-giving Nile, and many religious traditions continued and were consistent over 32 dynasties and over 2,000 years, although towards the end of the era, many times, they were ruled by outsiders -- the Persians, the Ptolemies of Greek Hellenistic culture, and, finally, the Romans.

♪♪ The Romans invaded the region in 31 B.C., a turning point in history as it heralded the end of Ancient Egypt.

♪♪ Egypt's fertile plains quickly became the bread basket for the empire.

It was said to feed the city of Rome for four months out of every year.

Can I try one?

Thank you.

Oh, ah, it's hot!

It's really hot.

Mmm!

And it's really good.

This flatbread is a staple.

You see it everywhere in Cairo, transported in vast quantities throughout the city, and it is delicious.

For millennia, whoever controlled the head of the Nile Delta could also control trade and the supply of wheat from the lands along the Nile.

That's why Memphis was sited here.

And now the Romans station themselves close by at a place called Babylon, named after the original city of Mesopotamia.

It was a defining moment for the development of the future city of Cairo.

This Cairo street follows exactly along the old riverbed of the Nile River in Roman times.

Today, I'm on this street, it is leading me to a beautiful church.

♪♪ Archaeologist Peter Sheehan has been studying this location for nearly 30 years.

Hi, Peter.

-Hi, Darius.

Morning.

-How's it going?

-It's going good.

Welcome to Old Cairo.

-This is amazing.

It just underlines, being inside a Greek Orthodox church, how multicultural Cairo really is.

-It is, and particularly Old Cairo, full of churches -- this Greek church, a synagogue, the mosques.

This is the church of Mari Girgis, Saint George.

You'll see him all around.

But we're not actually here to look at so much of the churches and mosques and the other buildings today.

We came to look at the Romans.

-Now, this is exciting.

-So, take a look down there.

-Okay.

-Tell me what you see.

-Whew, that's a big drop.

-This church is built on top of a Roman tower, so what you're looking at through here is three stories of the Roman tower, 16 meters high.

-That is fantastic.

Now, can we get down there?

-We can, of course.

♪♪ -Wow.

Is this right now Roman level here?

-This is Roman ground level.

Here's the tower on your left... -Wow, really impressive.

-...all the way up to the height where we were, effectively on the roof of the tower, which is where the church is.

-Okay.

It's so impressive that the Romans, wherever they went in their empire, they would build in standard ways.

So, here we are, way out in Egypt, building the ways that you'd see in Rome or wherever in the empire.

-Yeah, and usually because it's done by the legionaries.

-Peter is taking me into the heart of the tower.

Wow.

Now you've got this -- maybe a lower part.

Truncated columns here?

-Yeah, that's right.

These are the ground-floor columns still in place, and then, at a later point, they've been cut off, and a medieval wall has been built on top of them.

-And then, up there, I guess that's where we were standing in the beginning.

-That's right, in the church, right at the top of the tower.

♪♪ -After the fall of Rome, Christians in the 7th century A.D. used the abandoned tower as the foundations for a church -- the only circular church in Egypt.

♪♪ Later, in 1909, this new Orthodox church was built on top of the old one.

While the scan teams set to work, Peter is keen to show me evidence that the Roman tower is part of something much bigger, and it's just up the street.

It's another massive construction.

-Another massive round tower, like we had in the first one.

-Right.

So, here, you would've had -- -Central open space this time, lots of light.

-And you really get a really good sense of this colonnade here.

So, what to make of all this?

I mean, you've got two towers.

-You got it -- two towers.

This is the south tower.

The other one was the north tower.

So, here we are.

-Oh, wow.

-You tell me where we are.

-So these two towers?

-That's right, and this forms the western side along the contemporary line of the Nile.

-Okay, which is no longer here out on the street there.

-500 meters further to the west now.

-Okay.

-So, what we're looking at -- The two towers form the western side of the fortress of Babylon.

-The Roman emperor Diocletian oversaw the building of the fortress in A.D. 300.

The new fortress was crucial for trade along the Nile.

-We also have a good idea of why he built it in this spot, which was really to fortify the existing entrance to the Red Sea Canal, connecting the Nile to the Red Sea.

-There's a canal from the Nile to the Red Sea?

-That's right.

Just like the Suez Canal in the 19th century, connecting the Mediterranean ultimately with the Red Sea.

-This canal was over 100 miles long, a feat of engineering which allowed Rome to dominate trade to countries as far away as India, its entrance to the Nile protected by the Babylon fortress.

I want to see if the scans can tease out the extraordinary history of these very different buildings.

♪♪ At the top is the Orthodox church, with its ornately painted interior.

♪♪ Deep in the foundations is the Roman tower.

♪♪ When you take away the church superstructure, you see more clearly that this circular tower is the mirror of its sister.

♪♪ The two towers are on either side of the entrance to the harbor, guarding the meeting place of the River Nile and the Red Sea Canal.

Our computer reconstruction reveals the full extent of the whole fortress -- 400 yards by 200 yards, large enough to hold a garrison of 1,000 men.

This has been a truly remarkable story.

From the outside, you would never guess that the Greek Orthodox church here sits on top of a Roman tower.

You have to strip away the layers to reveal, and what you discover is that this entire area was once a massive Roman fortification with a channel that connected to the Red Sea and a harbor, and outside, there flowed the Nile, ultimately connecting this part of the Roman Empire with the rest of the Roman world.

♪♪ The Romans dominated Egypt for 600 years.

But by the 7th century A.D., a new empire was rising in the east.

♪♪ In A.D. 642, the Arabs conquered Egypt, bringing many new influences from the Middle East and beyond.

♪♪ [ Call to prayer in native language ] The religion of Islam was just 20 years old at the time, yet it would define the developing culture of the city.

These two minarets stand at the boundary of the old city.

♪♪ The invading Arab army had captured the Babylon fortress and established their own capital here at this strategic point on the Nile, the nucleus of the city that would become Cairo.

The actual origin of the name Cairo is obscure, and there are many versions.

One story is that the Arabs wanted this new city to conquer the entire world, so they called it Al-Qahirah, which means, in Arabic, the "conqueror."

The Western world has taken "Qahirah" and made it "Cairo."

♪♪ One of the greatest leaders of Arab Egypt was Saladin in the 12th century A.D. Saladin defended the Holy Land from the Crusader armies.

When he secured power in Egypt in 1171, he built a stronghold on a rocky outcrop overlooking Cairo.

Saladin's Citadel was to become the center of power for the next seven centuries.

To find out more, I'm meeting Jehan Reda, an expert in Arabic architecture.

Can you tell me a little bit about why Saladin built his citadel here?

-Well, maybe to defend the city of Cairo, but also for himself as a stronghold for himself and his family, and because it's the higher ground.

-So he's got a good lookout around at what enemies he'd need to repel?

-That's right.

-Who would those enemies be?

-Well, he was at war with the Crusaders.

They were at continuous warfare, and he needed to make sure that the cities were defended and that they were fortified.

The entrance is right here.

-Okay.

And we're at a pretty elevated point.

Jehan is going to show me one of Cairo's secret places, the Well of the Spiral, a medieval masterpiece deep below the citadel.

So, it looks like people don't come here too often.

-Well, no.

Actually, it's a little bit dangerous.

-Oh.

This well would provide the water to allow the citadel to withstand long sieges.

♪♪ So, this is carved right into the bedrock?

-Right into the rock.

And, actually, we're going down the staircase here, which wraps itself around the shaft of the well.

-Ah, wow.

-So, these are the windows.

-Oh, man!

Okay, that's a drop.

That's a drop.

That is deep.

Okay.

-Yeah.

There's so much rock that was cut through.

I just sort of think about engineering but also, you know, the labor force.

Do we have any idea?

Is this done by the military or...?

-Well, no.

Actually, we have an eyewitness account that places Crusader prisoners of war at the site.

-Prisoners of war throughout history get the short end of the stick and are made to do a lot of hard, backbreaking labor.

-Hard work.

-All right.

-Let's go.

♪♪ -Oh, looks like we're bottoming out here.

-Yes, we are almost there.

So, here we are.

-Wow.

-Uh-huh.

-Oh, yeah, it's one thing to look down, and it is another thing to look up.

[ Both chuckle ] -Yeah.

-This is even more impressive from down here.

-The 45 meters above you, you can see it all the way up to the sky.

-So, that's like 100, 125 feet or so, and then there's more.

-You're standing above it, actually.

So, the shaft, the continuation of this one, is right beneath us.

-My God.

So, they're more than a halfway point here, but how is the water getting to this level and all the way up to the top?

-All the way up.

So, we have a mechanical system made up of two water wheels who fit into each other.

-Okay.

-We have a set down here on this platform... -Right now?

-...and a set up there.

-Still today?

-Yeah, right behind you.

-Can we take a look at it?

-Right behind you.

-Oh, in the dark?

-Well... -You did say to bring a flashlight so... -Flashlights on.

-Ah, now.

-Hmm.

-So, how exactly is this going to be working?

-Well, they're powered by oxen, actually.

They walk around in a circle, turning the first horizontal wheel... -Okay.

-...which, in turn, turns the vertical one.

-The wheel lifted up the water in a series of buckets attached to a rope, all driven by the oxen.

-...all the way down the shaft.

-A miserable existence, and I'm thinking, again, can you imagine managing to get the oxen all the way down here to this depth?

-Yes, well, they used the spiral staircase to get them down here.

-Right, right.

-But, I mean, like, it's got to be a 24/7 kind of procedure if you want to.

-Hard work, yes.

-Really hard work, and I'm feeling really sorry for the oxen right now.

And then it continues up.

-And then it continues up using another system like this at the very top.

-That is unbelievable.

♪♪ Jehan told me that the well goes even deeper into a second shaft.

-So, that hole there is open, and if you fell down it, you'd go right away down the hole.

-Okay.

-With the help of a climbing expert, we can scan the lower half of the well to discover more about its remarkable engineering.

The scan team finally reached the level of the Nile.

This water was a precious resource back in Saladin's day.

It would've been cleaner back then.

Visiting Saladin's well was an extraordinary adventure, and understanding it -- many times, it's dark, the lighting is not very good.

It's a massive construction.

It's hard to get your head around just really what you're walking through, and I think that the scans are going to be able to give us a better sense of the construction of the well.

♪♪ The citadel sits high on its outcrop.

♪♪ As you come down, you see just how far the well shaft has to descend to reach the water table -- a remarkable 295 feet through solid rock.

♪♪ And the scans reveal how the two shafts of the well fit together, with a middle platform for the water-wheel mechanism and those ever-circling oxen.

♪♪ From there, the water was lifted up through the top section to come out into a reservoir like this in the courtyard.

♪♪ The well and its supply of water helped make the citadel impenetrable.

♪♪ [ Horns honking ] From Saladin's time until the 19th century, Cairo's leaders ruled from the mighty citadel.

During the later centuries, Egypt was occupied by foreign invaders -- the Ottomans, the French, and the British.

Finally, in 1953, Egypt broke away from British control and became fully independent once more.

Cairo is now the capital of a new republic.

[ Horns honking ] But of all the cultures that have ruled the region around Cairo, the one that continues to feed the imagination and inspire the modern people of this country is the civilization of Ancient Egypt.

♪♪ And that's largely due to the architectural jewel in Cairo's crown, the Great Pyramid of Giza.

Now I'm going to re-enter this world in a new way using virtual reality.

Ooh.

-So, welcome to our virtual studio.

-Very impressive.

What do you got in store for me today?

-Well, let me teleport you to the Great Pyramid -- so, a perspective that you've never seen before.

-All right.

Let's see.

♪♪ Oh, okay, I've never seen the pyramids like this before.

-[ Chuckles ] ♪♪ -We've got everywhere that we visited.

I see all the chambers here, just floating.

-We have a privileged, almost pharaoh-like view here of the inside of the pyramid.

-Oh, we just pass right through the walls, which is great because I can get a breath of fresh air.

That is really cool.

And down below, in there, we've got our subterranean chamber.

-This subterranean chamber here is really amazing, especially when you look up to align it with all the other rooms.

-It's amazing.

I'm below the subterranean chamber right now.

That is intense.

-See how all three of them align.

-Oh, yeah.

I never thought I'd be inside the pyramids on my back, looking up through the pyramids, through the chambers.

How did they do this?

The subterranean chamber is much rougher than the upper tombs, but its alignment suggests it was part of an original plan.

-Darius, do you remember this space?

-This is the Grand Gallery.

I mean, what an impressive space, except, instead of walking up it, we're kind of floating in the middle of it.

It's really cool.

At the top, I can just see in the distance there.

I can see floating out there the pharaoh's actual tomb.

-So, to be true virtual archaeologists, we really should enter the space as we did for real, crawling.

-And, actually, it really feels like we're back there.

And you don't want to bump your head.

Oh, yes, that is good.

I feel like I just relived that moment again.

That's fantastic.

[ Grunts ] -Although it seems very simple, the engineering required to make this space inside a huge structure is sort of incredible, really, to think about.

♪♪ So, we shrunk down the pyramid so that we could take this, like, beautiful overview of the whole Giza Plateau.

I love how Cairo, you know, laps up against the plateau of Giza as the river did many years ago.

-Amazing.

I'm sure the pharaoh would've appreciated this view, too.

♪♪ This has been one of the most amazing experiences I've ever had.

♪♪ Being in Cairo, I got a new appreciation for the depth and breadth of history.

Just think about the Romans.

We consider them ancient, but when they came to Egypt, they encountered a civilization that had already been developed and was thriving for thousands and thousands of years before them.

And it's all in the shadow of the Pyramids of Giza that are still awe-inspiring and timeless.

♪♪ -"Ancient Invisible Cities" is available on DVD.

To order, visit Shop PBS or call 1-800-PLAY-PBS.

This program is also available on Amazon Prime Video.

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