Original subtitles

Day is breaking over the Salisbury Plain.

We're about 75 miles west of London.

It's very early, and it's very cold,

but I for one certainly don't mind being up because today

I've been given a very rare permission to hike up here

before anybody else and to walk among giants.

♪♪

♪♪

Stonehenge, just the name is iconic.

They're 13 or 14 feet tall.

They're 7 feet wide.

They weigh 25 tons each.

And, you know, whole generations of people are going to be born

and live and die,

and yet, these stones will still be here.

They are a monument to time, and yet,

we still don't fully understand

the mysteries of Stonehenge,

who built them, and why, but I'm here to find out.

♪♪

Stonehenge, myth and legend have always surround its origins.

It's been called both a healing site

and a place of human sacrifice.

Was it a calendar or a stellar observatory?

Its construction has been attributed to druids,

the wizard Merlin, and even aliens.

♪♪

For centuries, historians have fiercely debated

the site's true purpose,

but now, for the first time ever,

they're coming close to solving the enigma.

Cutting-edge technology is revealing secret markings

etched into the stones.

Nearby, the revelation of other hidden monuments

is rewriting everything we thought we knew.

And a stunning discovery in the most remote reaches

of Great Britain may finally reveal

where the idea for Stonehenge came from

and expose the identity of those who built it.

♪♪

So get ready to join an expedition

to tackle the ultimate ancient mystery,

solving the riddle of Stonehenge.

♪♪

My name is Josh Gates.

Whoa.

With a degree in archaeology and a passion for exploration,

I have a tendency to end up in some very strange situations.

It's just straight down.

Unbelievable.

My travels have taken me to the ends of the Earth...

Oh, God!

...as I investigate the greatest legends in history.

[ Filtered voice ] We're good to fly. Let's go.

This is "Expedition Unknown."

♪♪

To kickoff my investigation into Stonehenge,

I began in the surrounding area of Wiltshire County, England.

These are some of the most charming towns

to ever thatch your roof.

And in case the cafés, hotels, and the bars don't tip you off,

folks around here are in the Stonehenge business.

One shop, catering to the crystal

and tree-worshipping set,

appears to have been built for hobbits.

I'm officially too tall for this shop.

Here, you can find a small rock to set any mood.

Red Tiger's Eye said to be a stimulating stone.

You know what that means?

Hard as a rock.

The new age shop is just one sign of the...

[ clears throat ] ...eclectic crowd

that the Stonehenge area seems to attract,

but it seems that everyone has a different opinion

about where the town's main tourist attraction came from.

It was, like, a meteorite, and it just blew up and went.

[ Laughs ]

Like a big massive time clock.

-Yeah. -Big massive time clock.

Mm.

The people who built Stonehenge act like a logical analog

of Lewis Carroll's Rabbit Hole in the mirror.

How did you go through a mirror

when the silvering is on the back?

Big party out there, lots of roast hog.

Clue me in. Who built Stonehenge?

Extraterrestrials that the ancient Britains

worshipped as gods, basically.

That settles that.

I'm also admiring this staff here.

If you hold him like that on the ground -- You want me to hold this?

I'd love you to if you can.

-Okay. -How do you feel holding him?

Uncomfortable.

Ooh, dear.

♪♪

GATES: Though these guys definitely

have some interesting ideas,

I'm eager to hear what the experts have to say

about why Stonehenge was built.

And to do that, I'm joining forces

with an all-star team of scholars

back at the site.

-Hello. Josh. -Hi, Josh. I'm Mike.

-Mike, nice to meet you. -Hi, I'm Susan.

-Susan. -I'm Rupert.

Rupert, pleasure.

Mike Parker Pearson is a leading expert

in the archaeology of Stonehenge,

and his recent findings are the reason I'm here,

but first, I ask him for a bit of Stonehenge 101.

So what is a henge? It's not the stones, right?

No. A henge is actually an earthen enclosure

with a ditch and a bank.

So if these stones weren't here, this would still be a henge?

It's still a henge because there is a bank

and ditch outside of it.

GATES: So that's one mystery solved.

Stonehenge isn't just a name.

It's a description of a stone circle

inside a henge that ancient peoples managed to plan

and construct in stages

between 4,000 and 5,000 years ago.

Historian Susan Greaney has studied

how they might have done it.

The smaller stones you can see around us here,

these have been brought from Southwest Wales.

It's about 180 miles away,

and we think they've been brought by the sea,

by boats and then over land to Stonehenge.

That's crazy.

Considering the complexity

and the difficult of the engineering,

do you think there was some centralized power

conducting this?

I think there has to be.

This is a work of genius.

There is so much thought that has gone into

every single bit of it.

The evidence we have is that this may well

have been a moment of cohesion

where people are bringing autonomous groups

together to all act in synchrony.

GATES: Mike tells me that 5 millennia ago,

Britain was populated by disparate groups of people

who were finally making the transition from hunting

and gathering to farming.

These weren't rouged druids like Spinal Tap

would have you believe.

Druids didn't even exist until thousands of years later.

No. These were surprisingly advanced Stone Age

or Neolithic people

who started working together on this massive project,

but its biggest mystery remains.

What the hell is it for?

For decades, many focused on the site's entrance.

It's aligned with the rising sun on the summer solstice.

So many believe it was intended as an astronomical worship

or a celebration site,

but recently an investigation turned up a macabre

find that began to change the accepted view of Stonehenge.

When we dug here, what we found was human remains.

That was just a fraction of the number of people

who were buried here.

This place was full of

the cremated remains of the dead.

It is basically the largest cemetery within Britain

for the whole of the 3rd millennium B.C.

Incredible.

So Stonehenge was much more than some ancient stargazing site.

It also appears to be a massive graveyard.

The connection between the two functions has remained elusive,

but in recent years, the magic of technology

has helped experts crack the code.

English Heritage, which maintains the site,

has been working on the most detailed scans

of the monument ever conducted.

The team behind the tech is here today.

-This is Steven and Antonio. -Hey, Steven.

Hi. Antonio, nice to meet you.

-Josh. -Hi, Antonio.

How are you? Pleasure to meet you.

They've been using 3D scanners

that showers the area with lasers,

mapping and measuring every detail of the landscape

down to fractions of a millimeter.

Some are mounted on tripods, but others,

like the Leica Pegasus Backpack,

are a bit more mobile.

That's a Dalek from "Doctor Who," correct?

-Correct, yes. Wearable Dalek.

-What is this thing? -It's a mobile mapping unit.

-Do you want to have a go? -Oh, for sure. I'd love to.

Okay. This is the coolest backpack I have ever seen.

So if I were to break this, what is the value of this thing

I'm wearing? -It's about $200,000.

Wait, it sounded a lot like you said $200,000.

I did, indeed.

This is literally worth more than everything that I own.

[ Laughs ]

GATES: I walk through the monument

with a laser scanner.

Talk about doing work on the go.

This thing has 32 individual lasers on board

that are capable of capturing

500,000 data points every second.

And the on-board cameras are able to see every single time

I take a step, generating 25 MGs of data every meter

that I walk forward.

In other words, this thing is able to see everything.

In the most recent rounds of scans,

English Heritage generated an incredible

850 gigabytes of data,

which has started to settle long-simmering debates

about the site's original function.

So the scan showed us that particularly in this direction

where the sun sets in midwinter.

Yet along the solstice alignment,

the stones were shaped much more carefully

than some of the other stones.

GATES: The scans reveal that special care

was used in constructing

and refining a specific viewing alignment,

not just the summer solstice,

but in fact completely the opposite.

Stonehenge seems to instead have been built to channel the sunset

on the shortest day of the year.

We've all been thinking about the midsummer sunrise,

but it now looks as though

the most important direction of sight

is through that gap, towards the midwinter sunset.

♪♪

GATES: Far from being an alter to worship the gods

who brought the light and warmth of summer,

Stonehenge appears to have been made

for the dark cold of an English winter.

And that's not all the data has shown.

One of the things the laser scanner also shows us

is the detail of the dressing of the stones.

And when I say dressing, what we mean is the way

that the stones were worked

and they were shaped using hammerstone.

You can see here these mushroom shapes.

So these are all Xs.

Look at that. That is spectacular.

The amazing detail uncovered 72 never-before-seen symbols

carved into the stones.

-Oh, here. -That's right.

GATES: Though more recent than the original construction,

the carvings here serve as a sort of nail in the coffin

for what Stonehenge was really for.

We only find carved Xs on slabs associated with burials.

♪♪

GATES: This, along with the winter solstice alignment,

supports Mike's theory that Stonehenge was actually built

as a monument to the ancestors,

a so-called land of the dead.

In and of itself, this is a bombshell revelation

for a site once thought to be a simple calendar

or a place of celebrations, but the question remains.

Why was Stonehenge built in this particular spot?

What makes this place special?

Mike leads me outside the stone circle

to reveal another amazing find.

Do you notice anything weird out here?

Well, you've got this kind of ditch mound here.

That's it. These banks are natural landforms.

GATES: The natural formation that was here

sits in an alignment with the stars and sun above.

To the builders of Stonehenge,

this made for the perfect spot to erect their monument.

What they did when they built Stonehenge was to embellish

this natural feature

that matches the movement of the heavens.

This may have been the center of their cosmos.

Does it lead anywhere?

Down to the valley, over that ridge.

There, we found another henge,

which has come to be known as Superhenge.

GATES: I'm sorry. Did he just say Superhenge?

♪♪

GATES: I'm on a quest to discover

the meaning of Stonehenge,

and I've just learned that the site was actually

a massive burial area.

Now, archaeologist Mike Parker Pearson

is leading me away from the site

along a secret avenue

that points to another hidden henge.

Josh, this is Superhenge.

Look at that.

It's massive.

Yes. It is the largest henge in the world.

Incredible.

GATES: Nearly two miles away, northeast of Stonehenge,

is an enormous bank and ditch construction.

With walls nearly 10 feet tall

and a diameter of 1,600 feet across,

it's more than five times

the size of the Earthworks at Stonehenge.

But what I do not see are any stones.

Yeah. This is all about timber.

GATES: Archaeologists here discovered a timber circle,

then another, then a third.

And then this last year, we discovered

that the whole thing was surrounded

by a giant timber circle.

Wow.

1,200 feet in diameter,

probably more than 300 giant posts,

posts the size of totem poles.

That is extraordinary.

The wood posts may be long gone,

but excavations inside this massive henge

have unearthed proof that the site wasn't

just for rituals or burials like Stonehenge.

They were surrounded by houses.

This is where people were living in their thousands.

So these are the people that are constructing Stonehenge?

Yes.

Linking natural landforms with these great monuments,

but to understand it best,

you've really got to see it from the air.

From the air?

♪♪

To show me the super side of Superhenge,

Mike takes me to a nearby airfield

where a helicopter awaits.

♪♪

Once we get airborne, we arrive over Superhenge.

The scale of the construction finally hits home.

From Superhenge, we fly on to Silbury Hill,

the tallest man-made mound in Europe.

Finally, we come upon the site that Mike is most excited

about showing me.

This is the town of Avebury,

which sits inside the longest stone circle in the world,

16 times bigger than Stonehenge.

It originally had 98 Sarsen slabs

running around the edge.

Stonehenge, a site that we think of as being without equal,

is actually part of a much larger network

of circular monuments.

There is the bank and ditch in nearby Superhenge

and a larger stone circle at Avebury.

So the question is, where did the idea for these henges

and stone circles originate?

Answering this question will mean

taking a journey back in time.

To get there, I'm riding in my own piece of English history.

♪♪

To learn more about the mysteries of Stonehenge

as well as the people who built it,

I'm traveling to meet archaeologists

working in a much lesser known,

but equally mysterious site known as Bryn Celli Ddu.

And to reach them, I'm traveling about 5 hours west

out of England and into Wales.

♪♪

From majestic castles to quaint village streets,

it's easy to see why this region is said

to have inspired Lewis Carroll

to dream up "Alice in Wonderland."

It's littered with beautiful sights and signs,

both short and really long.

It might even push the Mad Hatter over the edge.

What do you think the Welsh National Spelling Bee

looks like?

♪♪

Soon after crossing onto the island

of Anglesey in North Wales,

I finally reach the site I'm looking for.

♪♪

The ancient passage tomb of Bryn Celli Ddu

and archaeologist Seren Griffiths.

-Hello. I'm Josh. -Nice to meet you.

How are you doing? Nice to meet you, too. I'm doing great.

This, I'm assuming, is the site.

This is the site. This is Bryn Celli Ddu.

It's really beautiful. It's obviously a tomb.

-Uh-huh. -Yeah.

And so what are you investigating here?

What are you trying to figure out?

Prior to the passage tomb, there was a stone circle within it.

And the big research question is,

whether the earliest phase of it composes a henge monument.

And if it is a henge, why is that significant?

Because that would have been about 500 years

earlier than Stonehenge.

Incredible.

If this is a henge, it will be much older than Stonehenge

and offer potential insight

into the origins of the world famous landmark,

but to unlock the secrets of Bryn Celli Ddu,

Seren tells me we need a different point of view.

Mythic entrance.

♪♪

This is awesome.

-So on the solstice -- -Mm-hmm.

...the sun would have come right through here

and shined on this back wall. -Yeah.

That's outstanding.

And so to your mind, what went on in this room?

So we know that the cremated remains of a group of people

were deposited within the chamber.

Behind this chamber, we have a range of very weird

and wonderful things,

a human ear bone and a bit of frog --

-Wow. -...a witch's broom.

Yeah. So this was a place of magic? Yes.

This was "Macbeth" stuff. Yeah. Right.

Absolutely. That kind of ritual and ceremony.

Yeah.

There are so many dots here that connect to Stonehenge,

a resting place of the dead,

arranged with the solstice alignment

and used for arcane magic rituals.

There's even a ditch around the tomb.

To find out if there's an adjacent bank

hidden underneath,

which would make this place a henge,

Seren has enlisted the support of her partner,

archaeologist Ben Edwards.

-Hi. -Hi.

Josh, nice to meet you.

This looks crazy.

It's not too crazy.

-What is this? -This is a resistivity meter.

-Oh, of course. -Yeah.

That's what I was going to say, a resistivity meter.

You know, for those who don't know exactly

what a resistivity meter is, how does it work?

All it does is measure resistance. Got it.

So you got a current into the ground,

and it measures the resistance to that current.

So the bank of our henge, if there's one underneath,

that will be higher resistance. -Got it.

You can have a go if you'd like. Yeah?

-Yeah. -Oh, I would love to. Okay.

So all you have to do is press start.

It takes a reading. Lift it up.

-Okay. -That's it.

Put it in by the meter mark on the tape.

-There's your next reading. -Great.

-Do it again. -Okay.

So just every meter. Okay.

That's it. It's done. You've done the line.

So know we go have a pint.

-No. -No.

Do the rest of the square first. We go back the other way.

We do. Wait. Are we doing the whole field?

Yeah. Oh, this suddenly got a lot less fun.

[ Laughter ]

GATES: Ben has marked out the test path

with a measuring tape

so I don't take this resistivity meter too far astray.

Though, I'm not sure how much trouble

I can get into looking like an old man

with a tricked-out walker.

Okay. So moment of truth.

Lighter gray, high resistance.

So if we've got a light gray area,

that should be the henge bank. -Got it.

GATES: The results are in, and they are typically Welsh.

In other words, hard for me to read, but to Seren and Ben,

this pixelated image is as clear as day.

What's that?

That in there is a lighter gray area

right where the henge bank should be.

Is that a henge?

♪♪

GATES: I'm at a Stone Age tomb in Northern Wales

using state of the art geophysics technology

to determine if this monument was once surrounded by a henge.

That in there is large gray area

right where the henge bank should be.

-Is that a henge? -Yeah.

Yeah. That's a henge.

Doesn't look like much, but it is.

10 gray pixels.

That looks like it's confirming your theory.

-Yeah. -Wait. That's a huge deal.

-Yeah. -Yeah.

GATES: Then Ben shows me another visual reading of the same spot,

and there it is.

That is as clear as day.

-That looks like a henge. -Yeah.

So that makes it really old.

Yeah. Significantly old.

This is maybe 500 years older than Stonehenge.

That's incredible. So could it be the oldest henge?

There is one other significant contender for that.

-And where is that? -That's in Orkney.

An Orkney is...

-Very far north. -North.

An island of the north, north, north of the coast of Scotland.

Okay.

The builders of Bryn Celli Ddu

appear to have brought their influence down to Stonehenge.

The stone circle incorporated surrounding landforms,

advanced engineering, and ritual burials,

but further north could be an even older henge

and evidence of the people that started it all.

The next morning, I hop back into my Brit mobile

and embark on a 10-hour road trip toward Orkney.

3 1/2 hours in,

I cross the border into Bonnie Scotland.

I always think of Scotland as England's

slighlty-edgy older brother.

A bit rowdier, a bit drunker, been to jail a few times,

but a lot of fun.

My first mandatory pit stop is Urquhart Castle,

which dates back to the 13th Century.

As castles go, this one is a little rundown,

but since it's perched over Loch Ness,

I'm more interested in it as the best viewing spot

for the world's most famous monster.

Sorry, Bigfoot.

It says here there is a $1 million reward,

Brian, if you capture evidence of Nessie.

So pretty much the episode took a hard turn.

We're just gonna be staying here now.

-But don't we have to -- -We're staying here, Brian.

It's $1 million.

You keep looking through that camera.

Earn yourself a sweet $10,000.

10 grand?

15 grand, maybe. We can talk about it, Brian.

The point is, keep your eye on that lens.

Here, Nessie, Nessie, Nessie, Nessie.

You can't stay underwater forever.

♪♪

And from there, it's onward up the North Coast 500

AKA Scotland's Route 66.

The scenery is a quintessentially Scottish mix

of very old buildings,

medieval cathedrals, and quirky roadside attractions.

Oh, my god. There it is.

Yard hedge.

Very rare, unless you have a subscription to

an English Skymall catalog.

♪♪

With the sun starting to set,

I finally arrive at the end of the road.

Literally, there is no more land.

This is the very tiny village of John O' Groats,

population about 300.

We're at the very northeastern tip of Great Britain here.

This place has the unfortunate honor

of being named the most dismal town in Scotland.

Sure. It seems a little bit lonely, but what do you want?

We're at the end of the world.

♪♪

What's not to like here?

From stunning seaside cliffs

to a damn fine fish and chips stand.

That's it. Oh, man. Is that good.

John O' Groats is my kind of dismal.

They even have a charming inn at land's end that looks like

it was plucked out of a Wes Anderson film,

and it affords me a cozy room to spend the night.

♪♪

The next morning, I hop aboard a ferry

to the remote archipelago of Orkney.

Thank you.

Passage from mainland Scotland to Orkney's port of Stromness

is just 24 miles as the crow flies,

but this stretch of sea has bested

even the world's most seasoned sea seafarers.

This is known as the Pentland Firth.

The Viking Sagas talk about this sea consuming their ships.

And just a couple of years ago, it swallowed a cargo freighter

that's even larger than this ferry.

♪♪

Whoo-hoo. This is gonna be pukey.

♪♪

It's beautiful out here!

This beautiful North Sea weather.

♪♪

GATES: My search for the hidden origin of Stonehenge

has brought me from a tomb in Wales

to a treacherous ferry crossing.

We're sailing from the northern tip of Scotland

to the remote islands of Orkney,

that is if the waves don't get us first.

Whoo.

The key is just keep your eye on the horizon.

♪♪

Once inside the breakwaters of Orkney, the sea is calm.

And we dock at the charming, if isolated, town of Stromness.

♪♪

From here, I am crossing the island

to meet with archaeologist Caroline Wickham-Jones,

who has been studying Stone Age structures in the far

northern edge of Britain.

She's revealing to me a little known,

but jaw-dropping site called Skara Brae.

This is the best preserved Stone Age village in Europe.

This is insane.

♪♪

This is like "Hobbit" Middle Earth stuff.

You're seeing a house as it was left by by Stone Age villagers.

♪♪

GATES: Caroline has secured special permission for us

to get inside for a closer look.

This is not gonna be the most glamorous entrance.

There have definitely been advances in doorframe technology

since the Stone Age.

After a quick crawl through a prehistoric portal...

Wow.

...we emerge in a Stone Age domicile.

This is awesome.

Literally, we're in someone's home. Yes.

-Are these beds? -Yes.

Furniture made of stone.

And this awesome storage area here.

We think that they probably used them to keep things fresh

as a sort of Stone Age fridge.

You can rent this place in Manhattan tomorrow. [ Laughs ]

You'd get a lot of money for it.

This homey one-bedroom isn't just a fixer-upper with a view.

It's also the key to learning about how the people here

ended up influencing the building of Stonehenge.

One of the things that we find here

is highly-decorated pottery.

The very earliest states for this pottery are here in Orkney.

So it's being developed by the people who are living

in these sort of communities.

We also find pieces of this pottery down at Stonehenge.

Really?

What it shows is that there must be people

traveling from the north to the south.

That's a proof-positive linkage.

Absolutely. Yes.

GATES: As we've seen in Wales,

the people migrating south to present-day England

didn't just bring pottery.

They brought ideas, advanced engineering know-how

and their sacred rituals,

but what about stone circles and henges?

It turns out, those are here, too.

Caroline brings me a few miles up the road to a stone circle

that may be the oldest henge in the U.K.,

the Stones of Stenness.

Everything out here is so "Game of Thrones."

[ Laughs ]

♪♪

Look at these stones.

I mean, they're enormous.

♪♪

This site is 3,200 B.C.

So more than 5,000 years old.

We may have finally zeroed in on the earliest-known henge,

centuries older than Stonehenge

and older even than Bryn Celli Ddu in Wales,

but even if we found the part of the world

where these stone circles originated,

there's still one big question in my mind.

Even if this is the earliest henge,

where did that idea come from?

Why put anything in a circular form?

We think we may have the answer to that.

♪♪

GATES: Caroline has been part of a research project

that may have turned up a site that predates all of these

and that could be the henge that started it all.

And when she introduces me to her research partner,

I know getting there will be interesting.

Josh, I think you know Richard.

-Dr. Bates, how are you, man. -Josh, great to see you again.

-Good to see you again. -Good to see you. How you been?

-Not too bad. Yourself? -I've been well.

Good old Dickie Bates.

The renowned geophysicist and I have shared

some amazing adventures

searching for a lost mythical city in India

and hunting for a chest of World War I gold in Namibia.

And now, we meet at yet another remote corner of the world.

This time, on his home turf of Scotland.

I'm told there is a special site that I need to look at.

I think so.

And one that, you know, very few people have ever even heard of,

yet alone seen. -And where is it?

It's out there.

-In the bay? -In the bay.

There's water there today,

but if you go further enough back in time, that was land.

You could have walked here.

And we think it could relate to a lot of the early monuments.

Well, let's go look at it. How do we get out there?

Well, we got to find ourselves a boat.

Oh, boy. Have you been in boats with Richard before?

-All right. Come on. Let's go. -Let's go.

Let see what you got for us now.

I never would have expected that my quest

to find the origins of Stonehenge

would take me below the surface of the frigid

North Sea, but here we are.

And if my past work with Bates is any indication,

this investigation will be one wild ride.

♪♪

GATES: At the Bay of Firth in the remote Scottish archipelago

of Orkney,

I've joined geophysicist Richard Bates

and archaeologist Caroline Wickham-Jones

on a potentially groundbreaking

diving expedition to explore an ancient underwater feature

that may be the original inspiration

for sites like Stonehenge...

The boat is just down here on the left, Josh.

Yeah.

...but at the moment, there is one thing

that's dampening my excitement.

I feel as though I need to point out that it is snowing.

-Yeah. -Perfect diving weather.

♪♪

Today, Caroline and Richard have enlisted

the help of Teledyne BlueView,

a company that's developed

pioneering underwater sonar technology

often used on deep sea shipwrecks.

I'm hoping our boat isn't their next project.

♪♪

After gearing up, we venture out to sea,

and Richard tells me we've got a bit of a ride ahead of us.

About an half an hour out to it.

We're gonna get out into the bay.

It's a little bit rough

'cause the Northernlies will row in. How rough?

-You know... -Scottish rough.

-Scottish rough. -All right.

Hang onto something, boys.

♪♪

♪♪

Beautiful out here, Richard.

Where else would you want to be on a day like today?

Oh, I don't know, indoors, in dry clothes, at the movies.

♪♪

GATES: The further out we get,

the more the weather starts to clear.

And Caroline gives me the lay of the land

as it was over 5,000 years ago,

when the receding glaciers of the last Ice Age

would have given the North Sea a much different look.

What you have to do is strip the water away,

get your mind's eye back 5,000, 6,000 years.

Would have been gentle valley.

The sea would have been somewhere in that direction.

This would have been dry?

This would have been dry.

GATES: Richard tells me that over the years,

divers have explored these waters.

Just a few years ago, one finding in particular

really grabbed his and Caroline's attention

for reasons I'm about to understand.

Hey, Josh.

We're coming up on the site now in the middle of the bay here.

Gonna get a high-resolution sonar image

of what's on the bottom.

All right. Great. Let's see it.

Okay. Off you go.

GATES: Our first move is to break out

Teledyne's boat-mounted sonar imaging scanner

to get an initial overview of the site.

Some assembly is required, but once we've got it all rigged up,

it's an impressive piece of kit.

The sonar generates high-resolution

3D points clouds.

So we're hoping to get some very good details

of the area of interest.

We should see individual stones. Awesome.

The scanner is able to stitch together 3D sonar scans

in real time,

creating an image of the site from above,

but, first, we'll need generate the data

by taking the boat back and forth...Zamboni-style.

We are following where we are actually

sending these sonar signals onto the seafloor. Right.

So each little dot on there

is a real refraction from the seafloor.

Got it.

As we navigate back and forth over the site,

the computer begins stitching together the data.

Before long, something unusual starts to take shape.

So no question there's a feature down there.

There's a definite step in the landscape here.

That's fabulous. It's really clear.

Look at that. Look at the curve there.

-It's circular. -That's not ordinary.

So am I to understand that this is a monument?

Is this a henge?

Well, that's the $1 million question.

GATES: If Caroline and Richard can prove that people made

or even modified this site,

it would mean that this is the earliest man-made henge

and stone circle monument ever found.

Perhaps, the inspiration for all others that followed.

The only way for us to continue studying

that is to get in the water. -[ Laughs ]

Boy, you better have some seriously warm gear

on this boat.

So against my better judgement,

and open-ocean dive in near Arctic waters is on.

Jon's brought another scanning set up to document

the site in even richer detail,

but first, we'll need to squeeze into specialty

diving suits capable of keeping us alive in freezing water.

I feel like I look like the Michelin Man

and Richard looks like James Bond.

♪♪

We drop the anchor in to mark the spot and then bombs away.

♪♪

The feature is only about 15 feet deep,

but it feels like we're on another planet.

We swim closer to the center,

and the ground beneath us starts to rise.

♪♪

GATES: I'm in Scotland's frigid Bay of Firth below the surface

and getting up close and personal

with a strange formation

that we hope is the inspiration for all henge monuments.

We have the surface team

lower the sonar unit to the ocean floor,

and we prepare for

a hyperdetailed scan of the site.

Okay. We're starting the scan.

It's not recommended, but it is safe.

GATES: Richard and I swim out of the way

to let the scanner do its job.

So as the sonar scans around,

it will build up the 3D point cloud of that area.

GATES: It only takes minutes for the machine

to collect millions of data points,

rendering an image in real time.

So the scan is completed now.

Okay. Okay.

That's amazing, guys.

There is fabulous detail just even so quickly.

That's just incredible.

GATES: After hours in near-freezing water,

we're eager to make our way topside,

thaw out, and examine the scan.

♪♪

What do we got?

How cool is that?

Hey, it worked.

GATES: The combined scans from above and below

have come through crystal clear,

giving Caroline and Richard the most accurate model

yet of the mysterious underwater feature.

And you can really see the pattern, really.

Yeah. Absolutely.

It's a very distinct outer part of the circle.

The oldest henges, they occur in Orkney.

Well, they have to be inspired by something.

Our work here tells us that they would've seen this

on a land surface.

GATES: The formation we saw underwater

so reminiscent of the banks and ditches of Stonehenge

and Stenness may in fact

have been the reason for their existence,

as the people migrating south sought to emulate the site here.

It's impossible to ignore how similar it is

in some ways to these henges we see on Orkney and other places.

Do you think this is a part of that story?

The henges mimic it so closely.

It's got the platform, the ditch.

It's the same sort of size, but natural.

Yeah.

Is it a coincidence that we get something like this

where these sites are developed?

It could be a mother henge.

It turns everything on its head.

You wouldn't think that it would be the genesis

of something as magnificent as Stonehenge.

GATES: In search of Stonehenge's origins,

I've gone all around the United Kingdom,

traveling through time in the process.

♪♪

I've seen how technology is settling long-simmering debates

about the site's purpose.

While Stonehenge is a place of ritual,

it wasn't just used for celebrations.

This appears to be a cemetery,

a land of the dead,

but it's also a part of a much larger story.

It's connected to superhenges

and to monuments in Wales and in Orkney

that are older than we once thought possible.

And in cold Scottish waters,

the origins of all henge monuments

might finally be coming into view.

All of it tells a tale far richer than the popular myths

and legends led on of a restless and inventive people

whose perseverance, ingenuity, and creativity

would pave the way for the Britain

that so many love and cherish today.

Stonehenge will be here long after we're gone.

And as the sun continues to rise

and set across these mysterious stones,

I'm left marveling, not just at the monuments,

but at the people who lived, died, and endured here.

♪♪

On the next "Expedition Unknown"...

192.

We're getting rich today.

If you look here, there's a windmill.

That's the Chicago Water Tower.

My dad thought that he would find it very quickly.

If you look here, you can see the state of Florida.

She's the lion.

Nobody has figured that out before.

It's buried under a lion.

-Something. -Hold on.

-Oh, come on. -Wait. Is that it?

♪♪