-From the dense jungles of Central America, across the globe to the arid deserts of Sudan, pyramids stand as mysterious monuments to ancient civilizations.

People have gazed in wonder at the precision and the effort and the scale of this, and they have asked questions, as we will ask questions.

How do they build them?

Why do they build them?

-It's a resurrection machine.

-Right.

The entire pyramid is essentially a capstone on top of the hole.

What do we still not know?

And what are some of the crazier theories we've come up to explain those gaps?

-There is a line of thought that the very structure, the shape of a pyramid is somehow divine and can channel energy.

-It really is beyond what the ancients should've been capable of.

-I'm going to explore the mysteries behind these astonishing structures.

Oh, that's incredible.

There are over 5,000 pyramids on our planet that have intrigued us for millennia, but what better place on Earth to start than Egypt?

Oh, my God.

Helping me solve these mysteries will be archaeologist Raksha Dave... -Why wouldn't they pimp up their graves?

I would.

-...and Egyptologist Chris Naunton.

-In the Egyptian mind-set, there's something much bigger going on here.

-Was there any sense that the pharaoh, that they would become a star?

-Absolutely!

-So join me as we explore the mysteries of the pyramids.

Behold the magnificence of the Pyramids of Giza, built more than 4,500 years ago, at a time when Stonehenge was merely a ditch.

I'm starting at the biggest and most puzzling pyramid of them all, the last surviving Ancient Wonder of the World, the Great Pyramid of Giza.

This building has stood for more than 4,500 years, and for most of that time, people have been clambering over it, digging underneath it, have been inside it.

And yet, even now, in this age where we have all the world's information at our fingertips, this building asks more questions than it answers.

The Great Pyramid's imposing exterior hides a puzzling interior of narrow passageways and hidden chambers.

This is the entrance tunnel to the Great Pyramid at Giza.

All of this stone was put in place for one man, and this path should lead to the burial site of the Pharaoh Khufu.

Around 2600 BCE, it's believed that Khufu reigned for about 30 years.

He left seven sons, including two future pharaohs, as well as this astonishing building.

Oh, my God.

Oh, that's incredible.

Huge gallery, three stories high.

After navigating a series of hot, claustrophobic tunnels, I've emerged into the cavernous atrium called the Grand Gallery.

And this isn't even where they buried the king.

This is just the entrance hall.

What an enormous space.

I mean, you could really do something with a space like this.

I mean, obviously, this wouldn't just be the living area.

You could knock through.

Oh, no, wait.

You couldn't knock through.

It's an absolutely astonishing place.

Intended as a final resting place for Khufu, the pyramid draws me ever closer to its central chamber.

Oh, this is amazing.

Wow!

The burial chamber of the king.

What a huge room to be in the middle of such a massive building.

And that's a big sarcophagus.

Imagine being the first to come in here and then find... nothing.

Yes, the remains of Khufu aren't here.

No one knows where the remains of Khufu are.

That's just one of the many mysteries of these pyramids.

Fortunately, I have Egyptologist Chris Naunton on hand to enlighten us, and looks like he is also feeling the heat.

-Chris, how are you?

-Hi, Dara.

I'm good, thank you.

How are you?

-Overdressed is how I am, because this is hotter work than expected.

-It is a little warm.

-This is the burial chamber... We think it is, yes.

-...except that there's nothing in it.

-Yeah.

So, there's a bit of a problem there.

There is no mummified body of the king.

But then we've found almost no human remains in any of these pyramids.

These were all, we think, robbed a very, very long time ago.

-Is there also talk that there might be another burial chamber?

-Well, yes.

So, if you look closely up at these massive granite ceiling pieces, there are cracks along the sides, and these seem to have been repaired, perhaps at the time the pyramid was being constructed.

So what's probably happening is that this vast weight of stone above us here -- intimidatingly -- was causing these cracks, and there are people that have suggested that if this burial chamber was on the brink of failing, there's no way that they would have buried the king here.

They must have buried him somewhere else.

And there are other chambers in the pyramid we know about.

There are also potentially other chambers, or there's hints of other chambers, which we don't know so much about, so there is still this thought that maybe the king actually is still in the pyramid, just in the chamber we haven't found yet.

-And how do we possibly know that?

How would he... -Well, there are hints here and there that there could be cavities behind what we have thought, more or less up to now, to be entirely solid walls.

But, of course, until we can prove it one way or another, imaginations can run wild.

-So even with the journey just beginning, we have mysteries aplenty, and clambering through the innards of this building, feeling the sheer scale of it does make you wonder, why did they go to so much effort to build a tomb?

It's remarkable.

It's an incredible space.

-Yeah, I mean, incredible achievement.

But in the end, it's difficult not to ask yourself, you know, "So, why are they doing this?"

In the Egyptian mind-set, there's something much bigger going on here.

The reality is that Pharaoh is a god, and if you want things to continue and everything to be okay and Egypt to be the greatest, then you have to build these enormous monuments.

It does seem inefficient, as well as majestic and fantastic.

Because what we saw, there's not, like, another west wing, not like there's a lot of other stuff.

-Not that we know for certain, no.

-And because there's so much we don't know for certain, people have rushed to fill the gap with all sorts of outlandish ideas.

-The alternative... perhaps more spiritual or paranormal way of thinking about the pyramids and the Great Pyramid as this exceptional structure would point towards ancient Atlantis, an ancient race of people who had knowledge far in excess of what we have in the modern clay.

That they had technology that enabled them to build the Great Pyramid, to build things that no other civilizations had been able to achieve.

-Look, you know me.

I have no truck with this stuff.

But I can see how wild theories can spread when the pyramid itself offers so few clues.

I mean, it is also the most enigmatic of pyramids, inasmuch as there's no detail in there.

-Yeah, and so one of the reasons why we're so perplexed by so much of this is that, unlike for other monuments elsewhere, there's no inscriptions here at all.

But if we were to look elsewhere, we might be able to get more of an insight, and then maybe that will allow us to reflect more.

-So we should go see other pyramids, which would explain the whole role of pyramids better.

-I think that would be a good idea.

-Let's do that.

So I'm traveling 34 kilometers south of Cairo to find a more illuminating pyramid.

I've come to Saqqara to meet Salima Ikram, who I hope is going to enlighten me about what these pyramids were actually for.

-Salima.

Hello.

-Hello, Dara.

How are you?

-I'm doing very well, but I have many questions.

-Well, we hope we can answer them.

-Salima is an Egyptologist who specializes in ancient Egyptian funereal customs.

And this pyramid, built 100 years after the Great Pyramid, is of special interest.

-Mind your head.

-I will, yeah.

-You're a bit tall.

They weren't built for the large man, were they?

It's for a pharaoh called Unas and the first pyramid to have any inscriptions.

These are our first hieroglyphics.

-Yep.

This is it.

-Oh, well, this is very much what I was expecting.

And it's conspicuous in its absence in the Great Pyramid.

But these weren't presumably just for decorations.

-No, no.

These are actually a way for the king to become one with the eternal stars.

This is really the texts, the magic that get him from this world to the next.

-It's essentially a machine to get the king to the afterlife.

-It's a resurrection machine.

-Right.

-But that's what it is.

It is to protect the king, but it is the whole sort of infrastructure to go "whoop" into the afterworld.

-And so the idea was that, at some point, quiet point after the king had been laid to rest here, he would rise and read, from this, the instructions as left by the priests or... -Yeah.

-The legends go that, before entering the afterlife, Osiris, god of the underworld, presides over the judgment of the dead pharaoh's soul among 42 terrifying gods, including the Bone Breaker and the Eater of Entrails.

-If we go into his burial chamber, I can show you how it's laid out.

It's a bit like a bedroom.

-Oh, please do.

-Mind your head again.

-I will.

Every plea for innocence held immense significance.

Failure resulted in an agonizing second death.

This trial not only determined if the pharaoh would be allowed into the afterlife, but also the future of all Egypt.

This is absolutely gorgeous.

-Isn't it fabulous?

-If I rise from the dead, where am I supposed to start reading this?

-Okay, so, you've got the sarcophagus here, and the king is lying down.

And then the king sort of is supposed to rise out of his bedroom and suddenly see the first spell, and it says, "O Unas, arise."

And then he reads it spell by spell, and it gives him explicit instructions.

-And that's kind of the point, isn't it?

-This is why this was all done, because he had to rise up, become one with the eternal stars, and live forever.

And, of course, also part of his job was to make sure the cosmos was in balance and the sun rose and Egypt was safe, and so his resurrection was key to that process.

-To ask a very fundamental question, does it go left to right, up to down?

-Yes, it goes up to down.

The easiest thing to do is look at the way the animals are facing and read into them.

-Fine.

-Here, this is his name, and the bunny is a very nice way of finding him easily.

-Okay.

Fine.

Okay.

The great thing about the afterlife is that you could take a whole load of worldly goods with you.

The things that they brought with them, were they to guarantee a safe passage or were they things they would enjoy in the afterlife?

-You would have stuff that you wanted.

Because, I mean, if you're going to live in the afterworld, you want to live comfortably, so you better take it with you, because you don't know what's at the other end.

It might be a Holiday Inn rather than The Ritz.

-Yes, absolutely.

It's fascinating that, in Egypt, the pyramid was a kind of machine to protect the pharaoh and allow him to take useful things to the afterlife.

Over 2,000 years later, 11,000 kilometers away, in China, something similar happened.

The Chinese pyramids of the Han Dynasty are burial mounds built for powerful rulers.

In the tomb of Emperor Wudi, swords and crossbows were concealed to protect the emperor in the afterlife.

That was nothing.

1,200 kilometers away, Emperor Qin Shi Huang's tomb housed a terra-cotta army of 8,000 life-size soldiers to protect him in the afterlife, only unearthed in 1974.

Back in Egypt, the Pyramid of Unas that I'm exploring with Salima has also recently revealed a hidden secret.

-So, we could, if we get the lights off, perhaps... -Okay, we can do that.

Can we get the lights off?

-[ Whistles ] -Whoo!

Well done.

-Okay.

-Okay, let's see if we can... -Oh, my God!

-Can you see that?

-I didn't see that at all.

This ghostly figure was uncovered as recently as 2007.

A closer look reveals a king wearing the crown of Lower Egypt, a harpoon in his right hand, hunting a hippopotamus.

-No, it's hidden.

-The hieroglyphs only divulge the beginning of his name, but many Egyptologists believe this to be none other than Khufu.

But that is absolutely stunning.

Was this stone recycled from one of Khufu's tombs or temples or was it intended to honor this long-dead legendary king who built the greatest pyramid ever?

-So these places really are magic.

Pretty cool.

-Next, I go deeper into Khufu's mysterious journey into the afterlife.

Was there any sense that, like, if a pharaoh ascended, that they would become a star?

-Absolutely!

♪♪ -I'm here exploring the mystery of these magnificent wonders of the Ancient World.

-Hello!

Welcome to Egypt.

-And, as a bit of a numbers guy, I find some of the figures behind the pyramids' construction truly mind-boggling.

[ Camel grunts ] Perhaps the most incredible wonder about these pyramids is the sheer feat of engineering.

In that first 100-year burst of pyramid-making, they moved 15 million tons of rock from quarries to here.

There is a piece of granite inside this pyramid which weighs 80 tons.

And even these standard rocks here were being brought here at a rate of 200 to 300 every day, which meant that these rocks were being put into place one after another after another every two to three minutes.

And as if that formidable work rate isn't astonishing enough, archaeologist Raksha Dave has promised to show me something even more extraordinary.

Raksha, of all the amazing things about the pyramids, what's the most incredible thing to you?

-Well, I think the thing that's the most mind-blowing is just how accurate they are, that how the structure was built.

So, for example, if I get my phone out, I can show you, on my compass, if we're actually stood properly, it actually points to north.

-So in order to get true north, they would essentially use the stars.

That, presumably, is what they lined it up with.

-Well, there's another method that you can use -- using the sun.

So you can actually get a stake, put it in the ground during the summer solstice, and then you track its shadow.

And, obviously, they didn't have telly back then, so, you know, somebody could stand there the whole day and watch the shadow track around and mark its track.

Once you've got that, you can then get a piece of string and walk around and create an east-to-west axis.

And then you could then get your 90-degree angle off that and then point to true north.

-With just a stick, some string, and a good knowledge of the solar system, the ancient Egyptians achieved alignments maybe 40 times more accurate than you can get on the compass on your phone.

So perhaps the ancient Egyptians just wanted to build something that was really precise and aligned perfectly with the heavens, maybe to honor their dead king.

And because they knew their stuff, they could do it.

However, the perfection of the Pyramids has baffled and intrigued all that have seen them, including one famous little Frenchman.

-Napoleon.

-Yes.

-When he came here for his little campaign to take over Egypt and Syria in 1798, it was kind of like a bit of propaganda.

He obviously wanted to control trade routes, the Red Sea, so he brought all of these scientists over to kind of survey what happened in Ancient Egypt.

And there was a young chap called Jomard, who was 19 years old, and he was absolutely fascinated and taken with the pyramids.

He set about and measured them.

[ Laughs ] He got the height, the length, got really excited about it, and then started extrapolating wildly.

-Jomard concluded that the length from the midpoint of the base of the pyramid to its tip was exactly a stade, an old Greek measurement that was based on the circumference of the Earth.

But he got carried away and made a critical oversight.

-Was it right?

Not really, because he forgot one thing.

-Oh, yeah, this stuff, which we're only seeing a small section of here... -Yeah... -Which is -- Is "cladding" the wrong word to use?

-I would like to call it outer casing.

-There we go.

-That's my archaeological term.

-Okay, fine.

What's that, then, archaeologically?

-So, that's what we call the core.

-Right.

-They are blocks.

They're put together really nicely.

But then you want your building to look beautiful and pretty, so they had white limestone then put on the front, and it's smooth.

So you would've had just smooth triangular sides, and they would've looked spectacular.

I mean, can you imagine, just these pyramids -- -The remains of it are still at the top of the second pyramid, Khafre's pyramid, and that would have been all the way down.

-All the way down.

-Now, they've been removed over the years for other building work.

-Yeah, but Jomard forgot about it, so his measurements were inaccurate anyway.

-A later, more precise survey that revealed different dimensions didn't dampen Jomard's enthusiasm.

He spent the next three decades writing a book which continued to throw up speculative theories about the pyramids.

So, Jomard mismeasured the Pyramids, got obsessed with them, wrote a book about them, and, in many ways, his crazy extrapolations, his, like, leaping to conclusions has been the path ever since, that a lot of people have taken his work and other people's work and gone, "Aha!

Well, therefore, this is of greater significance than probably it is."

But, wow, people really run with it.

-They do.

-They do.

The precision and accuracy of the pyramids has strangely made them even more intriguing.

-The precision was outrageous for what was needed, if it was a tomb or if it was a temple.

You don't even get that today in some construction.

This is, like, better than you get in the modern era, so why were they going to these extremes?

Other people have actually suggested it's all about water, and there's, like, a water-pump theory.

And they would pump water in and out of it, and this would create an energy system, as well.

And so, when you go inside the Great Pyramid, it doesn't feel like it's a temple, doesn't feel like it's a tomb.

It doesn't feel like it's kind of this sacred space.

It feels like you're in a machine.

-Of course, there's no scientific evidence to back that up, but that level of obsession with the pyramids is nothing new.

Little wonder subsequent societies were obsessed with pyramids and all things Egyptian.

In 30 BCE, the Romans came to conquer.

Antony and Cleopatra had been doing their thing, and the style, elegance, and architecture of Egypt became wildly fashionable.

So much so that several pyramids were built in Ancient Rome.

The Pyramid of Cestius was built in 12 BCE using cutting-edge Roman building materials of the age -- a brick-faced concrete core with a marble veneer.

Standing at a height of 36 meters, it is just 1/600 the volume of the Great Pyramid and still straddles the Ancient Roman city walls.

The Great Pyramids of Egypt are 4,500 years old.

Their size, precision, and design has led to people speculating wildly on who built them.

Look, I'm a science nerd, so I'm left cold by a lot of these theories.

But I do wonder, why are they so prevalent?

I'm gonna talk to Nick Pope, who worked for 20 years on the MOD's UFO desk.

Nick, have the pyramids always been so attractive to alternative theories or is that a very modern thing?

-No, I think they've always held this fascination for people, and I think people forget just how old they are, that even by the time of the Romans, they were already thousands of years old.

And then, in the Middle Ages, there was religious speculation.

People were theorizing, for example, that maybe the devil had constructed them or maybe some of the biblical figures.

So I think there's been an enduring mystery.

-Well, so, describe for me some of the more commonly expressed theories.

-Well, I think they fall into two categories.

Number one is that there was a mysterious lost race of pyramid builders, people with ancient wisdom that spread that knowledge all around the world, and many indigenous cultures and other ancient civilizations have this narrative of people coming as teachers.

The related theory, which is Ancient Astronaut Theory, which essentially says that humanity had teachers, and those teachers were actually extraterrestrials who came here, were worshipped as gods, and then we constructed great monuments, structures in honor of them to commemorate this visit, perhaps even with their help or with technologies, techniques which they had shared with us.

-These things are fun, I find, the alien stuff, but I just feel it always gets in the way of what is a genuinely astonishing human achievement.

-Whatever the truth of this, I think the ancient Egyptians clearly did know much more about astronomy, mathematics, geometry, and architecture than we perhaps give them credit for.

-Nick, an absolute pleasure to talk to you.

Thank you very much.

-Thank you.

-Pyramids globally appear to be catnip for alternative theories, and speculation around extraterrestrial involvement is not confined to Egypt.

Over 2,000 years ago, in Mexico, the Mayans established the city of Palenque and built the Temple of the Inscriptions, which has been called the greatest Mayan funerary pyramid on Earth.

King Pakal is buried directly below the pyramid, and on the lid of its sarcophagus is a carving, which, again, in some people's minds, resembles an astronaut in a spaceship.

The position of his tomb is significant, hovering between the living and the dead, the world below and the cosmos above.

Now, with the heavens in mind, I decide to take in the night sky in Cairo with Egyptologist Arto Belekdanian to explore the relationship the ancient Egyptians had with the cosmos.

While this would have been an incredible vista back in the days of the pharaohs, there is now a city of 22 million surrounding Giza, and the glow of that means that -- Jupiter, and there's Sirius, and there's Orion, and that is literally all we can see.

But Orion is a good one to see at least because the belt of Orion, for a long time, people felt this was a very significant thing.

-Yes, it's called the Orion Correlation Theory.

-Right.

-And, basically, the idea is that the three pyramids of Giza are aligned.

Their positions relative to one another sort of mirrors the configuration of the stars in Orion's belt.

-Right.

-But there's really nothing to indicate that that's actually true, though.

-This theory gained popularity after publication in 1995 of the book "The Orion Mystery."

While the pyramids are roughly aligned like the three stars of Orion's Belt, there seems to be little evidence to prove this was intentional.

I mean, they're just three dots in a line.

Okay, I mean, that is a nice coincidence.

The other thing that's mentioned sometimes is that there are two vents, let's say, going out of the chambers in the Great Pyramid.

-Yes.

-And people have thought, "Oh, maybe they point to a particular point in the sky."

-In this case, we're actually on much firmer ground, because these -- they're sometimes called vents, sometimes called air shafts, but, in fact, they seem to be passages from the underworld out into the celestial realm with the king's ancestors.

So they're sort of, like, guiding you.

They're pointing in that direction.

-These shafts pointing to the cosmos have always created great debate.

In 2020, a robot designed by a team from Leeds University was sent into one of the shafts coming from the Queen's Chamber.

The shaft is just 20 centimeters square and points upwards at 45 degrees.

Breaking through a blocking stone, a small painted chamber was discovered, which has unusual markings.

-Alright, we're done.

-Whoo!

[ Applause ] -Deeper into the shaft, the robot encountered yet another blocking stone.

Frustratingly, this obstacle proved insurmountable, leaving the mystery unsolved.

But, that aside, the whole purpose of these pyramids was the notion of sending the pharaoh into the afterlife, and the afterlife was in the sky, wasn't it?

-Yes.

Certainly, we know, through text, that that is what the ancient Egyptians believed.

The king, upon death and ascending into the sky, he would become one of the stars.

-And was there any sense that, like, if a pharaoh ascended, that they would become a star?

-Absolutely!

But at no point did they go, "That new star hasn't appeared yet.

Where's that new star gone?"

-[ Laughs ] -"Promises were made of new stars, and the promises weren't kept."

Did the Egyptians have constellations?

-Oh, yeah, and they all had so many associations with different divinities.

-In fact, they had a rollicking good creation myth set in the heavens and starring the Big Dipper, constellation of Orion, and their favorite god-king, Osiris.

Osiris was a kind and wise ruler.

He did marry his sister, but, you know, things were different back then.

His brother Seth was strong but unruly and envious of Osiris, so he turned himself into an ox and kicked Osiris to death, therefore becoming king.

But never fear.

Osiris was resurrected by the magic of his wife/sister just long enough to impregnate her with a golden phallus.

Don't ask.

She then gives birth to a son, Horus, who would later avenge his father and recapture the throne of Egypt.

I love the stars because I love these big balls of helium that are exploding in the sky.

But I also love the fact that they are basically a map of the human imagination.

And every culture attached different stories and different myths and legends to them.

-It's wonderful.

-And the Egyptians are no different in that.

-No, they weren't.

-It's very nice.

It's glorious.

I mean, I wish we could see a star or two.

[ Both laugh ] Next, Raksha demands that I use my imagination for her latest revelation.

-That there was the harbor at the time that those pyramids were being built.

-But we're miles from water.

It goes without saying that most pyramids around the world took a phenomenal amount of human effort to construct.

The Egyptian pyramids, however, really have people scratching their heads.

They're so old and so precise and so gigantic that the big question still remains -- how were they actually built?

Well, we've seen how massive the pyramids are.

We've also seen, in conversation with Raksha, just how precisely built they were.

-Yep.

-But what -- The stone itself, what was that cut with?

-Well, we think that they were using harder stone pounders.

And then, in terms of the final parts of the cutting, they were using chisels made of copper.

-Copper is a soft metal.

-Yeah, exactly.

So it's all in the technique.

-I mean, to be fair, the lads are making a pretty good job of this.

They're denting it pretty well.

-Yeah.

The majority of the stone used to build the Giza pyramids is limestone, quarried locally like this.

But crucial structural components were made from granite.

-The limestone isn't as difficult to cut and shape and transport as the granite because it's much further distance, it's a much harder stone, it's got a high level of quartz in it.

But they did it and they did it abundantly in Ancient Egypt.

And so they had some technique to do that.

And if you look at it from a modern perspective, we have engineers who've looked at this and tried to re-create how they did it, and they believe they must have had electricity and power tools, because you need diamond-tipped metal kind of saws to go through the granite.

But when you look at some of the detail and some of the precision you find in Egypt, it really is beyond what the ancients should have been capable of.

-Well, they did it, even without power tools, 4,000 years before man harnessed electricity.

The estimated workforce of between 30,000 and 40,000 men must have known what they were doing.

Can I try?

-Yeah.

Yeah.

-Okay, so, I'm intrigued to know how -- that or that?

-Good.

-That there?

I think the accuracy is the biggest problem.

-This is good.

If civilization is ever gonna recover, then we're gonna need to relearn these skills.

-Look, I mean, this is -- I've got no transferable skills.

No, I'd be the guy telling jokes in the camp at night.

"Hey, what about that limestone, eh?"

That limestone that I've been hacking away at was clearly popular stuff when it came to building pyramids.

3,000 years after the Egyptian pyramids were built, limestone was also used as the primary building material in the Yucatán Peninsula in Mexico for the great Mayan pyramids at Chichen Itza.

Using chisels made from much harder stone, like flint and obsidian, they cut grooves that wooden wedges were then driven into, splitting the stone cleanly.

The Mayans employed advanced engineering techniques, such as arches and stepped construction, to build tall, steep-sided pyramids.

A bit like what I'm doing.

-Yeah, you're nearly there.

Only 7,000 more of these to go.

-How long have they been doing it?

How long have I been doing it?

Yeah, yeah?

-Perfect.

It's done.

-It's good?

Yeah?

-That's good.

-Thank you.

Thank you very much.

♪♪ ♪♪ Hang on, hang on.

-What's happening there?

Wow!

-You're kidding me.

God.

-That's so clever.

-Wow.

Right, and then they just square it off, and then Bob's your uncle.

-It's sort of reassuring, as well, when they -- When so much speculation is done over these, "Well, how do they do it?"

-Yeah, yeah, yeah, absolutely.

Yeah, yeah, yeah.

-Here's six guys doing it.

-A bunch of guys with the right knowledge... -Yeah.

-...the right tools, and, presumably, as with these guys, years and years of skills and experience.

-Yeah, yeah, yeah.

We've witnessed the evidence of what can be achieved with the simplest of hand tools, but what about the immense quantities of stone transported from hundreds of kilometers away?

Apparently, Raksha has some revelations in store.

Now, Raksha, in all her archaeological wisdom, said to me, "Why don't you meet me at the edge of the pyramid site at Khufu's harbor?"

This is very much the bit where the pyramids meet the city.

I'm not seeing any harbor here.

In fact, the only water here is the Nile, which is about 2 miles that way.

So, what's going on?

Where are we now?

-What do you think we're looking at?

-We're looking at Cairo.

-[ Laughs ] Well, I can tell you that there was the harbor that used to service the Giza construction site.

-Wow!

-You can see -- actually see the harbor wall there.

-Yeah.

But we're miles from water.

-Well, you say that.

If you actually look at the site, can you see the little damp patches everywhere?

-Is that groundwater, is it, coming out?

-That's groundwater.

From doing a lot of excavations and things like pollen analysis, and they found that there was freshwater plants that were growing in the bottom of an extinct branch of the Nile that ran all the way up here at the time that those pyramids were being built.

-4,500 years ago, Giza would have appeared very different.

The climate would have been wetter, and the vegetation more lush.

The River Nile flooded every year, a harbor was dug out, and the water would have flowed right to the base of the pyramids.

Barges and boats from Egypt and beyond arrived here laden with granite, limestone, wood, and all the materials needed for pyramid construction.

-So, it was so close by.

And then people would unload, take the blocks to the construction site just there, and shape them.

-Wow, that's incredible.

Archaeologists long suspected the use of boats to transport stone to Giza, but lacked any solid proof.

However, in 2013, one of the most important archaeological finds of the century provided the smoking gun.

Ancient fragments of papyrus found near the Red Sea finally confirmed the transportation of white limestone to Khufu's pyramid, in a kind of shopping list.

-It had lots of kind of quite boring inventories in there.

-Right.

-Feathers for this, leopard hide for this.

But in this, he does actually mention this harbor.

So, he does mention some blocks coming to the harbor here.

-The archive is the Diary of Merer, an overseer in charge of 160 men, and it details journeys from quarries 10 miles away to the Great Pyramid.

What have now become known as "The Red Sea Scrolls" appear to be hard evidence that confirms that the ancient Egyptians built the pyramids.

But, for some, it is not enough.

-Just because we have proof that people were ordering limestone to be taken to a pyramid, I don't think that invalidates the idea of there being a spiritual dimension to their construction.

Was there an outside influence in the construction of the pyramids?

You could, if you were so inclined, go down the ancient-astronaut, extraterrestrial road.

Is it a within thing, a human thing, to have had these great visions and ideas about how to construct something or did it come from without?

-This sort of speculation must be frustrating for academics like Chris, who spent their whole careers doing careful and precise scientific research on the subject.

-So, despite the fact that all the evidence we have suggests that these are monumental tombs, there are people that want to see them as being much older, not tombs at all.

You know, "Why would they build something so big?

You know, they were only, you know, relatively short.

It must have been giants!

It must have been something else.

Must have been alien technology, possibly.

And are they even tombs?"

I mean, for some people, even that's not very plausible.

"They must have some other purpose."

Why not an electrical hydraulic power station?"

That's a serious suggestion that people have made.

I think people want a wrapped mummy, you know, almost ready to sort of rise up out of the coffin and say, "No, it is me, it's Khufu."

Until we have that sort of amount of evidence, the door seems to be open for people to reinterpret these things as whatever they want.

-I know, but the thing on Brass Eye about how, actually, these are giant ears for a massive cat statue under the ground -- that's the one I believe.

-There's something in that.

-I believe that one.

Next, I unravel one of the great mysteries of the pyramids.

I'd have done it exactly like this.

-There you go.

-Yeah.

-Problem solved.

-There we go.

I mean, this Egyptology is a doddle, isn't it?

Step by step, we're unraveling the Great Pyramid puzzle.

But we still haven't got to the bottom of how on Earth the ancient Egyptians got over 2 million heavy stone blocks up into place.

We know where the blocks came from.

We know how huge these were.

-Yes.

-And I know how they do the first layer.

-Ha-ha!

Yes.

-But do we know how they do the second layer, the third layer, and all the way up?

-Well, the short answer is, no, we don't.

We know the Egyptians used ramps, and that ramp has either got to be ludicrously steep or it's got to be enormously long.

Can they really have built a ramp that's a kilometer and more long out of mud?

For some people, that's just not good enough.

-Experts have been debating the mechanics of how these huge blocks were raised hundreds of meters into the air for centuries now, and it appears no one can agree.

Over the past decade, French architect Jean-Pierre Houdin has been working on an intriguing theory.

Central to his idea is an internal ramp system, with the Grand Gallery playing a key role.

This is the Grand Gallery we've been in before.

-Yes.

-Still as hot.

-Yes, it is.

Sorry.

-And still is both astonishing, but also perplexing.

-It is just a fantastic, beautiful, mightily impressive space.

-Yeah.

-Why go to the trouble of building this enormous, extremely high passageway?

-It's an unnecessarily grand chamber, given that no one is supposed to ever see it, and it's not gonna help him on his way to the afterlife.

-Not as far as anything in here tells us, no.

And, actually, if you look closely again, there are a few clues here and there that might provide something of an explanation.

The blocks at the side, at this level, there are what appear perhaps to be little linear scratch marks, almost as though something has been sort of pulled along in this direction, very, very close to the wall, kind of banging up against it.

-Yeah.

-A little video here which has been put together.

-Houdin's theory suggests that the Grand Gallery was constructed to accommodate a massive counterweight system.

This involved a wooden carriage carrying some of the heaviest granite blocks along rails and rollers to get them up to higher elevations.

-So, we're kind of descending back through it now.

The theory is that, in fact, this is the means by which some at least of the very heaviest blocks, the granite blocks that are casing the burial chamber and the ones that are placed along the top, forming the ceiling, perhaps came this way and were dragged up here using counterweights and ropes.

-So like a cable-car system.

-Almost, you might say.

-Actually, I was wrong to say a cable car.

I meant funicular.

-Ah, now, if you'd said funicular to start with, then, yeah, absolutely.

-And you know exactly what I mean.

-That sounds sufficiently technical.

-It's a counterweighted system that would allow you to use one weight to draw the other weights up, and then all you have to do is lift that other weight again, pull another weight up.

-It could work.

-That's the way I'd have done it.

I'd have done it exactly like this.

-There you go.

-Yeah.

-Problem solved.

-There we go.

I mean, this Egyptology is a doddle, isn't it?

With all that sorted, I feel we can move on to King Khufu, who is still missing, but there have been recent revelations.

An international team of scientists using cutting-edge muon technology have been scanning the Great Pyramid and have unearthed not one, but two previously unknown voids within the pyramid.

When the first chamber they found was finally revealed with an endoscopic camera, it was found to be empty.

But there's another, high above the Grand Gallery, that is still to be explored.

It's tantalizing, the idea of there being more empty spaces.

-Yeah, Egyptology and, you know, the world of Egyptophiles loves a hidden chamber, you know.

And we know these chambers are often filled with treasure, so... [ Gasps ] ...you know, what could be here?

Of course, the next thing is we gotta -- we gotta get there, we gotta get inside.

-What would it take for somebody to actually take a drill to the inside of the Great Pyramid?

-Well, the authorities need to be really, really clear that there's a good, very valid, very strong reason.

-It dangles enigmatically.

-It does, doesn't it?

-Oh, this is why the show isn't called "Stuff We Know About the Pyramids."

-Right, exactly.

There you go.

-This is why the show is called "Mysteries of the Pyramids."

-Right.

-When I came to Egypt, my head was filled with questions about these maddening, enigmatic buildings, and my heart was filled with the desire to live like Indiana Jones for a while.

Well, a lot of clambering later, I have a lot of answers I'm very happy with about how they built the pyramids, indeed, why they built the pyramids.

Of course, now I'm wondering where Khufu's body is and what that cavity is that turns up in all the scans.

That's the problem with these -- they keep offering more questions.

So in the next episode, we'll try to address two of the hugest questions.

Firstly, why did they stop building pyramids?

And also, what is the final score in the eternal battle between pharaohs and tomb raiders?

Next time, I meet the boy-king who dodged the tomb raiders without a pyramid to become the most famous pharaoh of all.

Hello, Tut.

You're the most popular.

That's the way history works sometimes.

You're the one everyone knows.

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