♪♪ -Stonehenge -- Britain's Neolithic concentric circles of ancient stone, one of the most iconic and mysterious monuments ever constructed in Europe.

For generations, people have argued over its origin, its meaning, and its purpose.

But now a dedicated team of archaeologists and scientists have made an incredible discovery, one that rewrites the entire history of Stonehenge.

The story begins with a series of extraordinary digs conducted over the last 10 years, roughly 150 miles from Stonehenge in western Wales.

Using the latest science and their own determination, archaeologists have unearthed the remains of another immense stone circle, dismantled in order to create Stonehenge, a monument that stood centuries earlier, in another part of Britain.

"The First Circle of Stonehenge."

♪♪ -"Secrets of the Dead" was made possible in part by contributions to your PBS station from viewers like you.

Thank you.

♪♪ -In the south of the British Isles, on the high plateau of Salisbury Plain, stands Stonehenge, the most iconic prehistoric monument in Europe, built 4,000 to 5,000 years ago by a Stone Age people now long forgotten.

♪♪ The looming megaliths cast an impressive shadow, but how they ended up here is still unknown.

♪♪ The true origins of Stonehenge have remained shrouded in mystery.

But all that is changing.

British archaeologist Mike Parker Pearson leads a team that has been transforming our understanding of these ancient stones.

♪♪ -Although my work involves many different aspects, many different countries, Stonehenge I think really got its hooks into me.

As an archaeologist, you can't not be interested in Stonehenge.

-The huge Sarsen stones are what usually get the most attention, but Mike is interested in the often-overlooked bluestones.

-The bluestones are much smaller than the great big stones of Stonehenge.

They're generally not much bigger than the human frame.

-Mike's excavations in 2008 revealed that, despite their size, they are central to the Stonehenge story.

-When Stonehenge started out, it looked very different to how it looks now.

♪♪ -Mike's early work revealed the original configuration of Stonehenge.

♪♪ At the edge of the site, he uncovered a ring of ancient holes that used to hold the bluestones... evidence Stonehenge used to look very different from today.

These holes demonstrate that the original monument, dating from around 3000 BC, was an enormous circle made entirely of bluestones.

-So, this was a major surprise.

We'd always thought that the first Stonehenge was just a monument of earth, a ditch and a bank, but it had actually been a stone monument right from the beginning.

-For Mike, this revelation was the start of a quest to discover the origins of Stonehenge -- a quest that would stretch over more than a decade.

-To understand Stonehenge, the secret is in the bluestones -- to find out where they came from and why.

♪♪ -There is a long-held legend about Stonehenge, first recorded in the Middle Ages.

♪♪ It tells of the wizard Merlin, who led men westward, to Ireland, the Land of Giants... ♪♪ ...where he found the stones and, using his magical powers, transported them to England.

♪♪ -Mythology and archaeology make uncomfortable bedfellows, but sometimes there are kernels of truth.

We know about Troy from the stories of Homer, for example, and archaeologists have sometimes wondered, might there be something in the Merlin tale?

-There may be, because it turns out the original bluestones are not local.

-The bluestones actually come from the far west.

It's not Ireland, but it's almost there.

It's west Wales.

In fact, at the time that the story was written down, the west of Wales had actually been regarded as part of Ireland.

-Could there be an archaeological foundation to this fantastical story of giants and magic?

A century ago, archaeologists determined that Stonehenge's bluestone megaliths came from the Preseli Hills of Pembrokeshire, Wales, almost 150 miles west of Salisbury Plain.

This westerly direction fits with the details of the Merlin myth.

♪♪ In 2010, to understand why Stonehenge was built with stones from so far away, Mike went to Wales to hunt for the quarries where they were mined.

Little did he know that he would make a far greater discovery... that once mined, these ancient bluestones first formed an even older, long-forgotten monument.

This secret history revolutionizes the understanding of how and why Stonehenge came to be.

♪♪ The investigation to pinpoint the precise source of the bluestones in Wales gets under way.

♪♪ But the Preseli Hills are vast... and peppered with countless outcrops of volcanic rock, any one of which could be where the Stonehenge bluestones were mined.

♪♪ By comparing samples from the Stonehenge bluestones with rocks in the Preseli Hills, 20th-century geologists made a crude match with a couple of southern outcrops.

But Mike isn't convinced.

He wants to find evidence of quarrying activity, and to ensure he digs in the right place, he needs the most up-to-date geological analysis of the area.

♪♪ Geologist Richard Bevins has mapped and sampled hundreds of Preseli outcrops.

Each one is unique.

-Examining the rocks of this area, there -- there are subtle differences.

[ Clinking ] ♪♪ You have to have experienced a lot of exposure to spot the minor differences which become critical.

-Richard's research is critical when comparing the Stonehenge bluestones with the Welsh outcroppings.

But it alone is not enough.

With the help of Jane Evans, Mike and Richard also use the latest tools of geochemistry to learn more.

♪♪ -The idea that we might be able to use these methods to pin down the absolute origin, possibly, of some of these rocks was a fascinating challenge.

I don't think that it's ever been used in the archaeological context before, so I think this was a first.

-Bluestone samples from both Stonehenge and the Preseli outcrops are pulverized... [ Machine clacking ] ...transformed into the finest sand... then panned, like gold, to separate out the minerals.

-We can look at the chemical compositions of small crystals for lots of different elements, and then we can do a matching of those elements, almost like a fingerprint.

-A favorite mineral marker is zircon, nature's geological clock.

-Zircon is a very robust mineral that never gets affected by geological processes and is, therefore, very good for dating rocks.

-From the moment zircon is formed, the radioactive uranium atoms inside it decay into lead at a steady rate.

By measuring the ratio of uranium to lead in a sample of rock, one can determine a unique isotopic signature to calculate its precise age.

The results are game-changing.

The zircon age of the Stonehenge samples doesn't match the dates for the outcroppings suggested in the 20th century.

Instead, based on this key research and other analysis, two new outcrops are identified as the source of the bluestones.

♪♪ -That was a really exciting moment.

What the geologists had discovered was not just that archaeologists and geologists had been looking in the wrong place for the best part of 100 years, but that here was somewhere where we could actually find the quarry where monoliths were extracted.

-With the chemical analyses of the stones guiding them to look in new locations, Mike and his team have discovered the original Stonehenge quarries.

Reality is replacing myth, and the secrets that lay within the ancient quarries can now be revealed.

♪♪ But when were the stones removed from the quarry?

It's time to dig.

[ Indistinct conversations ] ♪♪ In 2014, a full-scale study at the outcrops of Craig Rhos-y-felin and the imposing Carn Goedog gets under way.

♪♪ The team is looking for signs that prehistoric people extracted stone here thousands of years ago.

♪♪ -We've got a date for 153, and it's everything above that.

♪♪ -It isn't long before the digs confirm what the geology had indicated -- clear evidence of quarrying of Stonehenge's bluestone pillars.

Some of it is in plain sight.

-What we've got here are pillars that have actually been detached, ready to go.

One here, one there, one there, and they're really like a pack of cards that have slipped, one, two, three.

Just here, we have a wedge mark where somebody has chiseled just at that point when these two were at the same height to actually split them off, and that must have been the moment when that fissure opened right up that this stone slid downwards.

-In the dig at the base of the outcrop, the team uncovers strangely positioned stones, suggesting the existence of a bluestone production line.

-These provide lots of pivot points so that you can actually swing and tip the pillar so the bluestone can then be balanced onto here, and then we've got one end on this trestle and another one on this one, and then you're poised to get the bluestone away and down to the valley.

♪♪ -But how did the stones travel nearly 150 miles to Salisbury Plain?

In the past, archaeologists assumed the quarries were located on the southern slopes of Preseli, which would have made it easier to move the stones by sea for the journey east and avoid trekking over mountains.

♪♪ But the recently discovered quarries are on the northern slopes of the hills, which suggests the stones may have travelled overland.

-I think that there's a much more plausible possibility that they took those stones as far as they could by land.

There's a much more feasible land route from the north side going round the Preselis and then picking up the natural routeways that have been formed by the system of valleys in South Wales.

-Dragging these stones, each the size and weight of a small car, almost 150 miles seems a staggering feat for Stone Age peoples.

Would it have been possible?

♪♪ James Dilley and Luke Winter are experimental archaeologists.

-The Neolithic period has a very small amount of fragmentary evidence, and what we can do with experimental archaeology is to start filling those gaps.

-They recreate circumstances as they were in the ancient past, using only materials and tools available then.

-So, the tools that we've found in archaeology may appear simple.

They're just rocks.

Some are sharp.

Some are pointy.

But actually, they've been very carefully made.

They've selected raw materials that lend their characteristics to work really well.

♪♪ So, the stone blade is actually housed inside this piece of red deer antler here.

And the protein that makes up this antler is so tough and strong that it's -- it's not going to break.

I would have to put this under huge force to actually break this, so it's really such a great material to be using as carpentry.

♪♪ -Here at the Ancient Technology Centre, they are testing whether the bluestones could have been transported on wooden sleds.

-If you consider the route, for example, from Preseli to Stonehenge, it's 140 miles across all terrains, valleys.

And so what -- what became really apparent was that we needed to work out a method that would encompass all those terrains and make it feasible -- how you can take a stone, encase it, so that you can drag it over any number of surfaces.

-Luke first experimented with this method in 2018, based on evidence collected from Indonesia, Germany, and even ancient Egypt.

-We looked at ethnographic evidence for the way that people have moved sledges in recent times, and we looked at pictorial references of how people were moving heavy things 5,000 years ago, and we incorporated that to develop the sledge idea.

The stone we're fitting the cradle round today is about 1.2 tons, and the bluestones that came from Preseli, they range in size from around 1.2 to about 3.2 tons, so this is the smaller end of the scale for the bluestones.

So, this is called a tusk tenon joint.

We have clear, really solid evidence for this type of joint from the Neolithic.

When it goes together, it's still reasonably loose, and the thing that tightens it is the peg that drives through the hole.

♪♪ -Experimental archaeology has demonstrated just how effective these Neolithic sleds could have been.

♪♪ -You can see we've got two ends of the rope running up the field.

We're going to split you down, 15 on each side.

-Today we're going to attempt to pull this with schoolchildren.

Obviously, we doubt whether the Preseli stones were moved by children.

We don't know that, but we assume teams of adults, muscular, strong, fit people.

So it's a real test.

-So, everyone's got a good, firm grip on the rope?

Yep?

No half measures.

Good, firm grip.

3, 2, 1.

Pull!

Go, go!

Go, go, go!

[ Children speaking indistinctly ] ♪♪ Go, go, go!

Someone tell us when to stop.

♪♪ Okay, drop the rope and give yourselves a big round of applause.

-I thought that was fantastic.

So, that was just pulled.

So, that's nearly 1 1/2 tons with the timber frame, and that was pulled by 30 13-year-olds.

We probably did 35, 40 meters up the slope, and it's up an incline, and I think it -- once again, it really -- it sort of shows that this -- this theory works.

You can pull a heavy weight on a sled on raw ground without the need for huge timber arrangements and sleeper trackways or rollers.

And actually, it was really surprising how efficient it became.

Half the team didn't even seem to be pulling much.

But fantastically successful.

-1, 2, 3, yay!

-Yay!

♪♪ -The quarry excavations revealed the ingenious stone extraction techniques of the Neolithic people.

And experimental archaeology has shown how the multi-ton bluestones might have been transported over land.

♪♪ Back at the quarries, the archaeologists have unearthed a new mystery sparked by the charred remains of a Neolithic snack.

In 2014, at the Craig Rhos-y-felin quarry, the team excavates hazelnut shells near a Stone Age fire pit... ♪♪ ...evidence a Neolithic person threw the remains of their meal into the fire at roughly the same time as the bluestones were quarried, preserving them for more than 5,000 years.

♪♪ The charred hazelnut shells were gathered and carbon-dated.

The shells were burned around 3300 BC, roughly 400 years before Stonehenge's bluestone circle was built.

-That leaves us with a mystery, because where did they go?

Did it take them 400 years to haul those stones to Stonehenge?

I suspect not.

I think that there's another place, maybe close by, that these stones were initially destined for.

-To explain the 400-year gap between quarry and Stonehenge, Mike theorizes that the bluestones could have originally stood in Wales.

Once again, the Merlin myth offers some perspective.

It describes not just stones but also an existing stone circle in the west, called "The Giants' Dance."

The team wonders, could the Stonehenge bluestones have been part of The Giants' Dance?

Is there any precedent for this type of monumental stone building in this remote part of Britain?

-When archaeologists talk about Preseli, they don't normally think of it as a great ceremonial center in Neolithic Britain, but actually, it's got one of the densest concentrations of Neolithic tombs anywhere.

-The area includes one of the pinnacles of Neolithic building activity, dolmens.

These gravity-defying structures were used as tombs.

The most famous Welsh example, Pentre Ifan, is only a few miles from the bluestone quarries where the Stonehenge slabs came from.

♪♪ There is substantial evidence that the Neolithic people of Western Britain were skilled stonemasons.

The people of ancient Wales had a culture of stone building that was largely absent in the east of Britain.

-Britain was a divided island when those earliest farmers arrived in the Neolithic, that, actually, the monuments and the pottery that they were using in the east as opposed to the west were substantially different.

-These two groups of people began arriving in Britain at the beginning of the Neolithic period.

Archaeological and now genetic studies show how they spread west across Europe, around the coasts and along major rivers.

DNA evidence reflects the two different routes the prehistoric Europeans took to reach Britain -- east from Calais and west from Brittany.

♪♪ Those who came from the western edge of Europe, settling in and around Wales, developed a distinct style of building huge stone monuments, unlike the people in the east of Britain.

♪♪ From modern France and Spain, up through Wales and into Ireland, the remains of a large number of huge Neolithic dolmens and other stone tombs can be found.

The people of the Preseli area were experienced in building stone monuments.

♪♪ Theorizing that an earlier stone monument in Western Britain would explain the gap between when the bluestones were quarried and when they were used for Stonehenge, the team's search intensifies in 2016.

In addition to the dolmens, the landscape around the quarries is scattered with standing stones of unknown age.

But there are no obvious indications about where the team should search for this original circle.

-How on earth would we find not just a stone circle, but a stone circle that had been taken down?

In other words, we were looking for something that would no longer exist above ground, and that's a big ask.

That's a real needle in a haystack.

And for a long time, I thought, what are the chances?

Very, very slim.

-To see the invisible, Mike once again turns to the latest science.

Aerial photographs are studied, and then aerial photogrammetry is used to map sites of interest.

From the photos, 3-D models are created and reveal hidden features in the Preseli landscape.

The geophysics team then analyzes promising sites with ground penetrating radar.

They also use machines that detect tiny changes in the soil's magnetic field that were caused by the heat of ancient fire pits and other human activity.

-It's a fantastic technique, because it enables us to cover these very large areas quite quickly.

And it can identify if there are actually monuments or maybe houses, ditches, pits, et cetera, that are often associated with the prehistoric archaeology we're looking for.

♪♪ -They are searching among the scattered standing stones and ruined monuments for traces of a circular shape -- something that could have been the original bluestone circle.

The data suggests many promising sites, but one, in a field called Pensarn, stands out.

-It's a low mound, but it could be a prehistoric monument.

And from that period of the Neolithic, we know that some of these mounds had surrounds of standing stones.

Now, of course we're a stone's throw in that direction from the main bluestone quarry.

We're a stone's throw from the smaller one, so this is the perfect position.

So who knows what we're about to find there.

-Encouraged by the scans, the search for the lost circle begins.

♪♪ -Stone circles are generally quite easy to find.

They've got whacking great stones in them.

What we are looking for is the depressions and the hollows that were left by the removal of the stones.

But also, don't just find a hole in the ground -- You have to find a hole with evidence of a stone being removed.

So we're looking for pits of a certain sort of size, in a certain formation, with certain characteristics, and it's not easy.

♪♪ -I think this could work.

Isn't it?

Yeah?

-The team quickly finds what they're looking for -- stone holes, just below the surface.

-We're looking at features, they're the size of the bluestone holes at Stonehenge.

♪♪ -And then there is more.

-So, what Lisa's just uncovered is that we have a -- a pit for a stone, a standing stone.

It's got the packing in it, but, totally unexpected, it's got the broken-off stump of the bluestone sitting in it.

So, this is the first direct evidence that these really are stone holes.

Marvelous.

We may have done it.

♪♪ -And that isn't all.

In a nearby field, the geophysics team has made another discovery.

-What we've found here is something very exciting.

We've got these big rings within the data set, and what we think they might be related to are circular enclosures, some of which are quite large, up to 40 meters across.

-It's possible they have found not just a single small stone circle, but a whole complex of them.

Now their findings must be carbon-dated to prove a connection with Stonehenge.

[ Indistinct conversations ] In the meantime, all the activity has sparked the interest of the locals.

Mike's talks at the neighborhood micro-brewery are packed.

-I think that is where the stone that ended up at Stonehenge was taken from.

Now today... -The dig is very popular.

We have gateposts that are huge standing stones or were once standing stones.

We've got standing stones in our fields that -- that we mow around in tractors, and, you know, they're -- They are everywhere, and you can't help but wonder why, you know, and what was it about this area?

-It's what we do this for, just to tell the story.

They're really engaged.

It's their landscape.

It's where they live.

You know, it's what happened under their feet 5,000 years ago, you know, where they walk.

♪♪ -We came up with a new IPA which is now one of our core beers.

We thought we would call it Hammerstone IPA.

So, could you guess who the image is based on?

[ Laughs ] -The team has made a strong start, but are they any closer to understanding the origins of Stonehenge?

[ Indistinct conversations ] ♪♪ The next phase of the dig begins in September 2017.

Mike has now been investigating Preseli for seven years.

But things no longer seem so promising.

The test results from the previous year's finds have proven disappointing.

Carbon dating reveals the Pensarn circle is in fact a bluestone ring, but from a Bronze Age tomb, 1,000 years after Stonehenge.

The team's hopes now lay in the excavations of the new circles detected by Kate's geophysics team.

But as the dig progresses, the likelihood that they are Neolithic quickly fades.

The stone artifacts found are uninspiring.

-Someone's thought, "I can make that into an ax."

-Mm, because the shape was already -- -Yeah, yeah.

Basically, you've got, yeah, what you might call trimming flakes, taken off both directions to give it the crudest of edges.

This is really scraping the barrel.

♪♪ -The team realizes this is not a Neolithic circle but an Iron Age settlement.

Once again, they are thousands of years off.

♪♪ -You think that, "That has to be it.

It has to be it."

Perfect prehistoric circular monuments, and you think, "Yes, this is it."

And even though it's tremendous archaeology, and anybody would be privileged to dig it, it's not what you're looking for.

-Whether we're ever going to find that stone circle, that former stone circle, that first Stonehenge, I'm now, I'm afraid, doubtful.

At that point, I was disappointed.

I thought that maybe we're not going to find whatever it is.

Maybe it never really existed.

♪♪ -They've now excavated every site on their list... except one.

♪♪ The remaining location is an overlooked collection of four bluestones on a site called Waun Mawn.

Waun Mawn means "peaty moorland" in Welsh.

Government archaeologists surveyed the site in the 20th century and described it as being "very small" and "unremarkable."

-We'd given up, really, on Waun Mawn, because the geophysics hadn't really produced very much.

Didn't pick up anything, no sign of other holes where stones might have once stood.

But there's nowhere else to look.

-Waun Mawn is now the team's last hope.

They dig with spades and shovels, the weather making their work even more difficult.

♪♪ -It is fairly extreme archaeology.

The weather isn't fantastic.

We are bailing water out of holes which will eventually again fill with rain.

I got sent to Waun Mawn as a bit of a forlorn hope.

It's wet.

It's exposed.

The wind never stops up there.

The students were rebellious, and we were all very tired.

We didn't expect to find anything, but you can't just chuck the job in -- "This is terrible.

The weather's bad.

Let's go home."

You have to excavate it.

-Sending Dave up the top of the hill to Waun Mawn was the last throw of the dice.

It was Last Chance Saloon.

But I'm glad we did, because it changed everything.

♪♪ -What's this?

It's definitely a fill.

That looks fantastic.

We've found this potential stone hole.

As well as color, which is darker, it's also a completely different texture.

It's softer, it's more organic, and it's clearly been disturbed.

So, you look for more, and we found another one at the other end of the arc.

When you start finding multiple stone holes with missing stones, that's the time to start getting excited.

♪♪ Mike's madcap idea actually had legs.

♪♪ -Where technology failed, hard work has yielded a breakthrough.

♪♪ But there is still more to be done.

The following year, the team continues their work at Waun Mawn.

The marshy soil means the geophysical technology is unusable, and the team must rely on their own experience and observations to find the holes.

-It's the texture that's -- that's really crucial and the sound that it makes.

When you tap the natural, and you tap the fill, there's a much hollower sound, an element of a drum to it.

It echoes a bit.

They are not easy to find, but once you find them, you very definitely know they're there.

-Now if we ever get a good day here [Laughs] we can see the mountains of Snowdonia.

If you look in that direction, you can see Ireland on a clear day.

So, these are really quite extraordinary locations for surveilling the world, and it may be one of the reasons that people are building monuments in such places.

Yeah, so, we'll come out three from here, and we'll come out three from there.

Going to put the kettles on.

Now, who's in charge of tea duties today?

-When you're on excavation, you forget about the outside world, and it's just all of you together.

There are people that you -- We've never been friends with at university.

We've known them for two years.

You go on an excavation with them, and suddenly, friendships are made.

It's this close environment where you don't have much personal space.

You don't have much time alone.

You're all wet, you're all muddy, and you just get through it.

And the way of getting through it is just by being friends, having fun, and just sort of embracing it as much as you can.

♪♪ -As one hole after another is unearthed, the shape of a circle is revealed.

♪♪ Its dimensions have the team excited.

-Its diameter, 110 meters, was exactly the same as the outer perimeter around Stonehenge.

♪♪ The chances of the two having exactly the same dimensions are really very slim.

Waun Mawn could be the predecessor for Stonehenge.

♪♪ -But is there any evidence of a direct connection between the two monuments?

♪♪ An oddly shaped stone hole provides an opportunity to use photogrammetry again.

-We could see the exact shape of the base of each stone that had stood in them, and one of them was very unusual, because it had a slightly kind of pentagonal cross-section.

And what was interesting was that there was one at Stonehenge which had a very similar form.

♪♪ [ Camera shutter clicking ] ♪♪ -Can they match the shape of the Waun Mawn hole to the stone at Stonehenge?

♪♪ It fits like a key in a lock.

♪♪ But this evidence alone is not conclusive.

The team still doesn't know when this circle was constructed.

Is it Neolithic?

And was it built before Stonehenge?

-[ Speaks indistinctly ] -The acidic soil has destroyed almost all organic matter that could have been radiocarbon dated.

♪♪ So Mike calls on the specialist services of Tim Kinnaird.

♪♪ ♪♪ -Well, we've got the section covered now, so I've covered it in the black cover and I'm going to go back under now.

I'm going to clean back an additional 10 centimeters so that I can go in and start to sample.

♪♪ -Tim isn't looking for physical objects.

He is interested in the soil itself, which contains traces of ancient sunlight.

-You can actually date sediments by measuring the remnant energy in the grains of quartz in that sediment since they were last exposed to light.

And it's a technique normally used by geologists, Optically Stimulated Luminescence.

OSL, we call it for short.

♪♪ He has to collect the samples under darkness so that he can be absolutely sure that the quartz grains within his block of soil have not been affected by light.

-They hope these samples of soil from Waun Mawn will reveal when the stones were originally set in place.

When the soil is bombarded by lasers in a lab, trapped electrons are released, revealing when the sample was last lit by the sun.

But the analysis takes months.

Will Waun Mawn prove to be from the wrong time period, as all the other sites have?

In 2019, test results arrive, and the OSL data gives a likely construction date of around 3300 BC... exactly what the team had hoped for after almost a decade of work.

-Well, that was a pretty good moment.

We had dated the thing, and we knew that it was shortly before Stonehenge.

♪♪ -Fantastic news.

Absolutely fantastic.

I'm over the moon, not just for myself and the team, but for Mike.

It must have been a great weight off his mind that here he is.

He's done it.

His theory's right.

He's bang on the money.

-Mike and his team have made a groundbreaking discovery and unveiled a long-forgotten chapter in the history of Stonehenge.

After years of searching in the wind and rain, they found the lost circle.

♪♪ ♪♪ The research proves that the bluestones of Stonehenge first stood in the Welsh hills, centuries before being raised in Salisbury Plain, by a people steeped in a culture of megalithic architecture.

♪♪ But what was the purpose of Stonehenge?

We can only speculate.

Mike's theory is that it was a place to venerate the dead.

-Everything we've been learning about the megalithic monuments is that they represented or even were considered to be the ancestors, whether they were components of tombs, whether they were single standing stones or stone circles.

♪♪ Stone is permanent, like the ancestors.

♪♪ -Mike believes it was not just a place for remembering the dead, but also a marker in time.

♪♪ He calls in archaeo-astronomer Clive Ruggles to examine the site.

♪♪ -Well, this is a Total Station, but what I'm using it for here is for measuring the azimuth of the sun, the bearing of the sun in the sky.

We can work out where all the astronomical bodies, the sun or the moon or whatever we're interested in, rise and set and would have risen and set in the past.

-Mike thinks that the Neolithic people would have aligned the circle to key times of the year, linked to the position of the sun -- the solstices.

-They are the turning points of the year.

So, from the deep gloom of midwinter, the knowledge that actually the land will become warm and fertile again.

And equally, midsummer is the peak of that fertility, and that that, too, is about to change as the days become shorter.

So, it's actually the movement of the sun.

It's something that is utterly permanent and eternal, like the ancestors themselves.

-Where the sun rises will have changed over the last 5,000 years by about the diameter of the sun.

So, if we're looking -- Where the sun rose on the longest day then would be about a sun's diameter further to the north than it does now.

And when it rises at midwinter, about the same further to the south.

So, we can -- we can make that correction.

♪♪ -Clive has found that Waun Mawn's stones do indeed show a solstice alignment.

♪♪ Two stones, twisted at right angles, form a target that aligns with the midsummer sun as it would have risen 5,000 years ago.

♪♪ It seems Waun Mawn was an important site for the Preseli people.

So why then were these stones moved more than 140 miles to the east?

♪♪ In the Merlin myth, the stone circle was stolen.

♪♪ The legend holds that Merlin came west with a large army.

Could the peoples of the east and the stone builders of the west have been at war, a war that would cause the easterners to steal the Waun Mawn circle?

There is little to support this theory.

Evidence of large-scale warfare at the time is as insubstantial as Merlin himself.

♪♪ Instead, there are signs that Waun Mawn is an example of a different kind of revolution that eventually spread across Britain.

♪♪ Stone circles first began to appear on Britain's west coast around the same time the bluestones were mined, 3300 BC.

♪♪ Waun Mawn was at the forefront of this new style of stone monument, which seems to be part of a greater cultural intertwining.

-What's interesting was that differences were beginning to be erased -- that actually, people were using the same pottery east and west.

They were building the same kinds of monuments, new circular forms like henges and stone circles in east and west.

-The later eastern circles appear to have been inspired by their western counterparts and were always built with local stone.

But the Stonehenge bluestone circle is unique.

This is the only circle known to have been relocated.

♪♪ It wasn't just inspired by the west -- It was built from western stones, despite there being viable quarries local to the Stonehenge area.

So, if an army did not steal the Waun Mawn circle, are there any traces of the people who did move the stones?

♪♪ When Mike's team excavated Stonehenge's outer circle, they unearthed thousands of fragments of cremated human bone.

♪♪ People were buried around Stonehenge almost as soon as the bluestones arrived.

But who were they?

♪♪ By analyzing the type of strontium in the bones, scientists can determine where they came from.

-People talk about you are what you eat.

Basically, the strontium isotope composition that you pick up is related to the composition of the food you eat, and the composition of the food you eat is related to the soil and the underlying geology.

♪♪ -When a team at Oxford University conducted a strontium analysis of the bone fragments, the results were surprising.

Many individuals from the earliest burials were not from the area.

Jane Evans illustrates the data.

-So, you can see that here's Salisbury.

We've now put in what would be a local value, and it highlights basically the areas that are chalk, in southern England.

So, anybody with a value like that was probably certainly living there when that bone formed.

However, some of them had higher values.

The areas where those slightly higher values come from are typical of Wales.

Those individuals could well have come from in and around southwest Wales.

-This looks to me like a migration signal.

This is the beginning of a group moving in, settling themselves on Salisbury Plain, and then their descendants continuing to live in that area.

♪♪ -To Mike, the bones at Stonehenge suggest these stones were not stolen but may have been brought by a group of people who themselves were moving east.

♪♪ But why would the Preseli people move their ancestral stone circle to Salisbury Plain?

♪♪ It's now believed they may have been drawn by a unique feature of the landscape.

♪♪ Beneath the soil of the Stonehenge ceremonial avenue lies a series of glacial channels in the chalk, stretching nearly 500 feet to the northeast.

5,000 years ago, these channels would have been visible and, by coincidence, aligned with the solstice sun.

Today's Stonehenge is clearly aligned with this natural feature, similar to the original bluestone circle in Wales.

-So, my guess is what we're looking at is people actually bringing their very identity, their ancestral identity with them to reposition themselves at one of the most important ceremonial complexes within Neolithic Britain.

-Around 3000 BC, people from the Preseli Hills may have been drawn to Salisbury Plain because of its natural solstice alignments.

Mike's theory suggests that they brought the stones with them to remember their ancestors and mark the eternal cycle of the sun.

Salisbury Plain was about to enter its golden age.

♪♪ The construction of the Stonehenge bluestone circle may have inspired others who saw it, becoming the seed for the creation of even greater monuments.

♪♪ Less than 2 miles from Stonehenge lies Durrington Walls, the largest Neolithic site ever discovered in Britain.

♪♪ At a time when settlements were rarely more than a house or two, the site was a temporary home for thousands, a pop-up town full of builders.

Around 2500 BC, its residents constructed a huge wooden circle, called Woodhenge today.

Around that same time, they repositioned the bluestone circle, adding the huge Sarsen stones that define Stonehenge.

Salisbury Plain now had two complementary sacred monuments.

-The stone circle of Stonehenge was a place associated with the dead.

Woodhenge was actually a place associated with the living.

♪♪ -Animal bones excavated at Durrington Walls show it was a feasting site, unmatched in Neolithic Britain.

♪♪ It was a place for the living to celebrate, next to a monument to the dead that stood the test of time, with Welsh bluestones at its heart.

But Stonehenge began with that forgotten stone circle in the Welsh hills... the original location of Stonehenge's bluestones, now rediscovered thanks to Mike's determination.

♪♪ -The big story is that Stonehenge is built out of another monument.

It's not the stones themselves that are important.

It's the monument that they came from.

And this really has to change the way that we think about Stonehenge, because you're actually linking two not just places, but communities and their monuments together.

This has been a 10-year search, and we've finally got there.

It's a great feeling.

And as you can tell with this wonderful weather, we're really looking forward to coming back.

♪♪ -Despite all of his work, Mike still has many questions he wants answered.

-So, I think there's every possibility that there are more stone circles to be found.

Looking for these sites is like a needle in a haystack, and I think it's something that I'm not going to give up on until hell freezes over.

♪♪ -An unlikely discovery on a hillside in West Wales has rewritten the history of Stonehenge.

♪♪ The monument's connection to Wales is deeper than experts ever thought.

♪♪ And in an astonishing, historical breakthrough, we now know that the stones of Stonehenge didn't just come from Wales.

They first stood in Wales... in a lost circle... that has transformed our understanding of Stonehenge and Neolithic Britain.

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