Original subtitles

NARRATOR: Mysterious stones appear to be making their way

across one of the hottest deserts in the world.

- Visitors begin to notice something bizarre

along the surface of the cracked lakebed.

- These strange rocks seem to have all travelled with ease

across the flat.

NARRATOR: An expansive ancient site

is revealed in a remote Chinese desert.

WAKEFIELD: This site is 500 years older

than the first lengths of the Great Wall.

What is this place?

NARRATOR: And enormous ice-age bones are discovered

in the high desert of New Mexico.

- This could help rewrite everything we know about human history

and about ancient migration patterns all across the world.

NARRATOR: Astonishing discoveries unearthed

from the depths of the desert.

Ancient lost cities. Forgotten treasures.

Mysterious structures.

Extraordinary curiosities, once lost to the sands of time,

are finally revealed.

As new technology uncovers remarkable tales

hidden beneath the deserts of the world,

the secrets in the sand will finally be exposed.

On the border of California and Nevada,

in the heart of Death Valley National Park,

lies the remains of a long-dead lake.

- Death Valley is the hottest place in North America,

with the record temperature reaching an incredible 57C.

As the name implies, not much can live or grow here.

NARRATOR: This lake is almost entirely dry throughout the year.

It has a cracked mud surface,

except for during periods of heavy precipitation,

and even that quickly evaporates.

The area is unbelievably flat.

It's almost seven square kilometres, roughly the size of Gibraltar,

and has less than a 4cm elevation difference

from its north to south end.

- Over multiple visits to this rare site situated in the Mojave Desert,

visitors begin to notice something bizarre

along the surface of the cracked lakebed.

CANTOR: What they see is entirely impossible!

Only after returning again and again,

to verify the facts with their own eyes, could they be sure.

The rocks are actually moving.

- Understand that these are not rocks rolling downhill

or stones being pushed around by waves.

These are rocks of varying sizes,

moving along the flat earth as if by magic.

- No-one has actually seen the rocks moving in real time.

But the trails left behind the stones,

and the changes to their location over time,

make it clear that they actually do move.

What is going on here?

- The lack of vegetation in this region

means there is really no wildlife here

capable of pushing stones of this size around.

Nor are their footprints or machine-made tracks

alongside the stones indicating that people were them pushing around,

so we know it's not a hoax.

LEONARD: The rocks really stand out

on top of the light, dusty mud surface.

They look almost alien to the landscape,

like they could be an art installation project

NARRATOR: The rocks moving across the lakebed

originate from the dolomite cliffs located to the south.

Freeze and thaw periods in winter cause the cliffs to crack,

sending rocks hurtling to the ground.

- These strange rocks can weigh as little as 85g,

or be as heavy as 315kg.

And they seem to have all travelled with ease across the flat.

- Regardless of their size,

the rocks appear to bulldoze the lakebed,

creating raised edges along their path,

while leaving smooth trails behind them.

NARRATOR: It's called the 'Racetrack Playa'

after the deep trails etched into the mud by the travelling rocks.

This strange and mysterious phenomenon

has drawn the attention of the science world.

Death Valley is a place of extremes,

featuring rarities like Badwater Basin,

the lowest point on the continent,

and the 2,000-year-old Ubehebe Crater.

- These rock trails can be several centimetres to several metres wide,

and anywhere from under a metre in length to well over 30m long.

One rock was even found to have travelled an astonishing 450m.

- The rocks leave a very shallow impression,

only about 2.5cm deep,

and usually take on a zig-zag design.

And interestingly, most of these trails

begin far from the edge of the lake,

as if they appeared out of nowhere.

NARRATOR: While the trail seems to run in all directions

and vary in lengths, each distinct trail leads to a stone

with a low pile of dried mud at the end.

- Rocks positioned together at the start of their path

might travel in tandem for a while before randomly diverging

and changing direction.

And even stones that share a similar size and shape

might not travel the same distance.

- There are many variables that affect the movement of the rock,

such as size, weight, shape, composition.

And that movement can clearly be tracked by the trails.

But how? How are they doing it?

- They are commonly called 'sailing stones'.

So perhaps, like their name implies, they are being blown by the wind?

NARRATOR: Powerful and persistent winds carrying fine grains of sand

can transform landscapes,

even carving away a rock's surface over time.

- But can wind really push a rock like a sailboat?

NARRATOR: The Coyote Buttes, lying between Utah and Arizona,

are sandstone waves that undulate along the horizon,

created over hundreds of millions of years by wind and rain.

The hoodoos in the Alberta badlands are striking sandstone pillars,

capped with rock tops that have been whittled away

by high wind and weather.

- Wind and weather absolutely affect landscapes,

altering their appearance over time,

especially when those landscapes feature sandstone.

But examples like the hoodoos refer to the wind moving along the rock,

not the rocks being moved by the wind.

- So wind alone doesn't seem responsible,

but could water make the mud of the lakebed slippery enough

to cause the rocks' movement even though the Racetrack Playa is flat?

NARRATOR: 10,000 years ago,

Death Valley went through a period of extreme climate change

that left the lake completely dry.

- While it is referred to as a lake,

it's not part of your average lake system,

where you have rivers and streams

moving water from high to low elevation.

- This lake is actually an endorheic basin with no outflow,

meaning the water can only escape through evaporation.

- It's possible a heavy rain could create a muddy 'slip and slide',

but without an external force acting on it,

the rocks still wouldn't be able to move.

- One theorist wondered if high winds could provide enough force

to move the rocks along the slippery mud.

They even went as far as bringing a light plane to the flat

to test how much wind it would take.

NARRATOR: After wetting a small area of the terrain

to smooth the cracks in the mud,

an airspeed of 68km/h was used

to try to blow the stones along the playa.

- He found little to no success:

even when they observed the rocks sliding a bit,

the wind caused so much rippling in the surrounding mud

that it altered and obscured the rock's telltale trail.

- Not only that, but the presence of the dry, flaky earth

built up in front of the rocks,

and the continued presence of the cracked earth along the trail,

indicates the movement was happening

when the lakebed wasn't entirely muddy.

- Ultimately, it was calculated that the force of wind necessary

to move a 3kg stone...

would be a whopping 180km/h,

a velocity well above the average wind speeds

recorded here on the playa.

- (wind howls)

- So, if it's not wind or mud creating a slip and slide,

what else could be causing this astounding movement?

NARRATOR: Speed is difficult to observe from a distance,

and The Racetrack Playa is a heavily protected natural wonder

that limits visitation for fear of tampering and disturbance.

Researchers wanting to place GPS tracking systems

on the sailing stones to accurately track their movements

were denied by the authorities, so they were forced to get creative.

- They returned to the playa armed with time-lapse cameras,

wind gauges and thermometers.

They even brought dummy rocks equipped with tracking devices

in the hopes of capturing the faintest of movements.

- These 15 dummy limestone rocks were from the Darwin Canyon,

which is an area of similar geological age to the playa.

LEONARD: Though Death Valley is the hottest place in North America,

its winters can be quite cool and wet, relatively speaking.

Over the season, the playa can be covered

in a few centimetres of snow, and snow can be slippery.

So perhaps the snow has something to do with the rock movement?

NARRATOR: Experts use time-lapse photography to capture the sun

melting the ice and snow, creating shallow, clear ponds.

These ponds then thaw during the day, only to freeze at night,

repeating the process again and again

over a period of weeks, creating small ice floes.

- An ice floe usually refers to a large sheet of free-flowing ice,

at least 20m wide and up to 2m thick.

Some ice floes can get bigger than 10km.

Clearly what is discovered here is different

and on a much smaller scale.

- Eventually, after decades of unanswered questions,

and failed theories, the team finally recorded evidence

of the Racetrack Playa rocks moving.

NARRATOR: Researchers working in Death Valley, Nevada,

were amazed when they finally captured

evidence of what appeared to be rocks moving.

The movement occurs when the thin, 3mm-6mm ice sheets begin to melt.

As they melt, they break apart under light wind.

The wind is then able to push the ice sheets,

taking the attached rocks along for the ride.

The winds are blowing at a mere 18km/h,

a tiny fraction of the hurricane-force gales

that were part of the earlier hypothesis.

- These extremely thin panes of ice, up to tens of metres across,

freeze around the rocks and then drag or pull them along,

which explains how the parallel trails are created.

MIFFLIN: Not only that, but the size of the ice sheet,

and depth of the meltwater around each rock,

impacts the direction, speed and duration of the time the rock moves.

This helps explain changes in direction

and length variability of the trails.

NARRATOR: These rocks are moving,

but at a near imperceptible snail's pace.

This rare occurrence only happens once or twice a year

when the conditions are perfect.

- In the end, it was never simply one thing.

It was a perfect storm of elements

that all have to be present for the rocks to move.

Water, sun, ice and wind.

I guess you could say they solved a rockin' mystery.

NARRATOR: 100km from the city of Yulin,

on the southern edge of China's Ordos Desert,

are the dusty hills of the Loess Plateau.

- The Loess Plateau is named for its silt-like sediments

that are deposited over time by the wind.

It's unlike any place else in the world.

- The arid countryside supports little vegetation,

and looks nearly uninhabitable, yet it is home to many people

who have been tied to these lands for generations.

NARRATOR: Archaeologists working in the region heard rumours

that along the west bank of the Yellow River,

rare stones were found in the crumbling Great Wall of China

and went to investigate.

Taking a closer look, experts noted something strange.

- Locals have been aware of the crumbling rock walls

around the area for as long as they can remember.

They live among them, but they never gave them much thought.

They were always assumed to be a section of the ancient structure

known as the Great Wall of China.

NARRATOR: Built over 2,000 years,

the Great Wall is the longest man-made structure on the planet.

It traverses over 21,000km

of Northern China and Southern Mongolia

and is a wonder of the ancient world that has stood the test of time.

It's a perfect illustration of the innovation and engineering prowess

of the Chinese people.

- The ancient barrier of the Great Wall

does cut its way across this dusty plateau,

traversing more than 1,500km through the Loess.

But this crumbling structure is not part of the Great Wall.

So what can it be?

NARRATOR: The Great Wall is made of brick, stone,

wood and other materials,

including a mortar that's made with sticky rice.

However, in this region, it also includes rammed earth

and stones composed of dusty loess soil,

making it look very similar to this strange wall.

- Not connected to the Great Wall, these walls are 2.5m wide

and sit 1m above the ground

in areas where they haven't been entirely buried by the dust.

NARRATOR: While examining an area of the wall

that had collapsed many years ago,

they found strange and rare stones

that don't appear to be part of the structural build.

These are jade pieces that have been embedded in the wall.

For many years there were rumours of the stone being stolen by looters.

- The placement of the jade pieces in the wall

is not construction-related,

and definitely not a practice used when building the Great Wall.

- These jade pieces, many of which fell into the hands

of distant collectors - can be traced to the Liangzhu culture,

which existed between 5,300-4,300 years ago.

NARRATOR: The Liangzhu culture was centred

over 1,600km away from the site,

and the jade is an indication of ancient commerce

as well as evidence of a connection to distant lands.

Experts believe that the jade was placed

as a symbol of spiritual significance,

perhaps for protection or to ward off evil.

The walls are not only made of stone

but are also reinforced by huge cypress beams,

a practice that is believed to have started during the Han dynasty.

- But carbon dating of the beams indicates that the wood is, in fact,

from 2300 BCE.

That is 2,000 years before the Han dynasty ruled.

NARRATOR: They uncovered structures spanning over 400 hectares of land.

The outer wall makes a 4,200m crescent shape around the site,

while the interior wall has a 5,700m circumference.

- Whoever built these walls took advantage

of the natural hilly terrain,

allowing it to act as a barrier where needed.

WAKEFIELD: These walls would have required

a combined 125,000 cubic metres of stone.

It's an incredible undertaking for the time,

so they must have had really good reason to build it.

NARRATOR: This region of northern China has a history of conflict

between the farmers of the Chinese lowlands

and the herders of the Mongolian steppe that still goes on today.

Eventually, the Great Wall was built here,

protecting China from the nomads to the north.

But whoever built this place clearly already felt threatened

long before the Chinese decided to build it.

ELLIS: It's not just a fortified outer wall,

but there are rammed earth platforms,

gatehouses and watchtowers.

They indicate this place was designed for security and defence.

So, perhaps the walls are part of a fortress or military outpost?

NARRATOR: Archaeologists uncovered a main access point,

along the wall at the northeastern edge, known as the east gate.

The entrance is surrounded by gate towers and guard houses

that would have been manned around the clock.

- The gate covers an area of about 2,500 square metres

and sits at the highest point of the wall, making it highly visible

and providing clear views of the plateau...

and anyone making an approach.

- Interestingly, the gate was designed as a one-way entry:

a style known as a baffle gate,

using a curtain wall to control the flow of traffic.

NARRATOR: On either side of the entry, there are bastions:

structures built at an angle to allow for defensive measures

in several directions at once.

- They, too, were formerly understood

to have been innovations of the Han dynasty.

NARRATOR: While examining the gate,

researchers found two rectangular pits

containing a cache of human skulls, but no other remains.

Tests revealed that the majority of the skulls were female.

- These pits were hidden beneath the foundations of the east gate,

with 24 skulls per pit.

They were likely sacrifices made at the time of construction

as a blessing for the project.

If so, they are the oldest evidence that we have

of human sacrifices in China.

NARRATOR: The Shang dynasty reigned from 1600 BCE to 1046 BCE

and practised human sacrifice.

Their kings, acting as both political and spiritual leaders,

oversaw the rituals of beheading,

burning and boiling people alive.

At a site in Yinxu, archaeologists uncovered hundreds of human

and animal remains, and based on physical evidence,

as well as ancient texts,

they estimated that over the course of 200 years,

over 13,000 people were sacrificed there.

Making them over 1,200 years older

than the skulls discovered at this site,

which has revealed practices and innovative designs

previously unknown to scholars of Chinese history.

WAKEFIELD: The design of the gate and the outer wall

makes it clear that this site was built for defence, like a fortress.

But the equally fortified interior wall suggests

that there was something requiring another layer of protection,

but what was it protecting?

NARRATOR: Moving along the site,

archaeologists made a groundbreaking discovery.

Towards the centre of the interior wall,

along the eastern edge of a hill,

they uncovered an extraordinary structure.

- It's a pyramid: an enormous rammed-earth and cut-stone structure

that rivals the pyramids of Egypt,

which were built around the same time.

NARRATOR: Standing 73m tall,

it's only half the height of the Great Pyramid of Giza,

but its base is four times the size,

spanning 240,000 square metres.

- This immense and imposing structure would have been visible

from every point of the surrounding plateau.

NARRATOR: The pyramid has eleven tiers

with buttresses supporting each level.

The top has an area of 80,000 square metres,

surrounded by walls measuring between 3m and 7m high,

and contains evidence of a stone reservoir,

roof tiles and pillars.

- The highest step of the pyramid was likely home to elites

who lived under the protection of the site.

NARRATOR: It's believed that at one time, a large palatial complex,

made of packed earth and wood,

was built along the pyramid's highest tier.

The surrounding grounds within the inner wall

revealed several residential areas,

temples, cemeteries and workshops.

This is not just a fortress but a monumental, neolithic city.

And at over 4,300 years old,

it would have been the oldest and largest in China at the time...

perhaps even in the world.

And yet there is little to no written record of its existence.

- Beyond the remarkably crafted structure,

evidence like the jade pieces, including moulds for bronze blades,

suggests that this was a bustling metropolis

with an extensive economic reach.

- Historians long believed that Chinese civilisation began

many hundreds of years later in the Central Plains.

But this site, now called Shimao,

has shifted their understanding by 500 years.

NARRATOR: Only a small fraction of Shimao has been fully excavated,

and it's assumed that new discoveries

will continue being made in the future.

But Shimao is already giving archaeologists a new way

of looking at the development of early Chinese civilisation.

The high desert of New Mexico is part of a vast plateau

significantly larger than the Australian state of Victoria,

which covers extensive parts of four different American states.

CANTOR: This high desert is part of a huge geologic formation

called the Colorado Plateau.

It's an incredibly interesting place.

- The Colorado Plateau is most famous for the Grand Canyon,

but the entire area is just a feast for the eyes.

- The pale colours of the land speak to the fact

that it only receives a few hundred millimetres of precipitation a year.

NARRATOR: In 2014, while hiking the plateau

in an area between La Joya del Pedrigal and Rio Puerco,

about 2,000m above sea level,

a hiker spotted what looked like a pointed bone

protruding from the dry earth.

HARIDI: Along with the pointed bone are four others:

a jaw bone as well as three ribs.

These bones are big, so obviously they belong to a very large animal.

CANTOR: The area used to be home to animals such as the grizzly bear,

grey wolf, wolverine and bison,

all of which are mostly gone due to human activity.

However these bones don't appear to be from any of those animals.

So if not them, then what animal could it be?

NARRATOR: After a hiker in New Mexico

discovered the bones of a very large animal,

archaeologists were called to the site to investigate...

and immediately found more bones.

CANTOR: The pointed bone is not so much a bone as it is a tusk,

and a very peculiar, easily identifiable one at that.

That tells me this tusk likely belonged to prehistoric megafauna

that once roamed across the American steppe.

That leaves us two possibilities: the mastodon...

- (roars) CANTOR: ..and the mammoth.

LEONARD: The mastodon's tusks were straight,

while the mammoth's tusks curled in towards each other.

So it's likely that these bones belong to a mammoth.

- The archaeologists find that many of the bones have been broken,

and quickly determine that they actually belong to not one

but two woolly mammoths.

Discovering the remains of one mammoth would be a rare occurrence.

But two? That's really a once-in-a-lifetime thing.

NARRATOR: The remains were found to be of a young female,

who was most probably the mother of the second mammoth

in the bone pile, a calf.

HARIDI: Mammoths would have called high plateaus like this one home,

but around 10,000 years ago, they suffered a catastrophic habitat loss

as a result of climate change.

This caused their eventual extinction.

But how did THESE two mammoths die?

NARRATOR: Only a few metres away from where the bone pile was found,

the archaeologists also discovered an obsidian projectile point.

LEONARD: This is basically a weapon made from volcanic rock.

It likely would have been attached to a shaft

to make a spear or an arrow.

NARDI: They quickly determine that it has the telltale shaping

of a Clovis-period projectile, meaning it was skilfully crafted,

with grooves cut into the surface along the edge.

And it's shaped like a leaf.

And given its design, it is, of course, incredibly sharp.

HARIDI: The Clovis era refers to a roughly 300-year period

between 13,500-12,700 years ago.

This is when the culture, and its technology,

appeared and spread across the Americas.

- In archaeological terms, the Clovis period is defined

by the spread of this particular kind of technology:

projectile points that were fashioned in a very specific manner.

- This seems to be an ancient kill site,

so could this mammoth have been brought down by Clovis hunters?

NARRATOR: The archaeologists carbon-dated the bones

and were astonished to discover...

that they were approximately 38,000 years old.

And, therefore, these mammoths couldn't have been killed

by Clovis-era hunters.

- This is truly remarkable, because the general consensus has been

that humans only arrived in the Americas some 16,000 years ago.

So how would this be possible?

LEONARD: The accepted theory is humans first arrived

in the Western Hemisphere via the Bering land bridge

that connected today's North America with East Asia.

CANTOR: We have long tried to map out

migration patterns into the Americas,

and often ignored the evidence present

in indigenous oral histories.

But academic perspectives are changing when it comes to the value,

and accuracy, of oral histories.

Even so, we always look

for other supporting evidence to back up our theories.

HARIDI: In order to be certain that this is a kill site,

the archaeologists need to inspect the bones,

looking for telltale signs of butchering,

or processing, of the two animals.

NARRATOR: CT scans revealed that the bone breakage

was highly patterned, a technical term meaning that specific force

had been applied to specific places, causing shards to break off.

CANTOR: The shards are what are called butterfly fragments.

It's a term used to describe when blunt force is applied

to one side of a bone but the opposite side breaks,

sending fragments flying.

- Butterfly fragments are an essential find here,

because only humans are capable of causing such damage.

NARRATOR: Every bone, except for one, showed perimortem damage,

meaning damage caused at the time of death.

In other words, there was no indication

that the bones had time to heal.

HARIDI: Finally, the CT scans reveal several bones have been punctured,

likely in order to drain the marrow.

And in order to do so,

you would need a good fire to melt that marrow into grease.

- They also found signs of a sustained burn,

meaning that someone was likely watching over it.

- It's clear that the mammoth was butchered by humans,

and this would have taken place 20,000 years earlier

than what was previously thought possible.

- This is truly a fascinating turn of events.

This could rewrite everything we know about human history

and about ancient migration patterns all across the world.

NARRATOR: Archaeologists must question...

when humans may have arrived in North America.

The oldest human remains and DNA found in the Americas to date

were found near Wilsall, Montana.

In 1968, a construction worker

unearthed scores of prehistoric tools,

as well as the skull of a child, at a location known as the Anzick site.

LEONARD: It turned out the tools were all patterned

in the familiar Clovis style.

The skull itself was roughly 12,700 years old,

and it belonged to a child of the ancient Clovis culture.

- This little boy would've been the descendent of an Asian population

that migrated across the Bering land bridge

around 16,000 years ago,

meaning most indigenous groups in the Americas today

can trace their ancestry back to these specific people.

LEONARD: But how could people have been in the Americas

almost 40,000 years ago when these mammoths were around?

Who were they?

- Despite most of those indigenous to the Americas descending

from an Asian population group that arrived around 16,000 years ago,

they weren't the only ones to have populated this hemisphere.

So who else did?

NARRATOR: Researchers have found that the Surui and Karitiana,

people indigenous to the Brazilian Amazon,

carry traits more closely related to Australasian population groups

than they do to Asian groups.

- This is fascinating. This means that the same people

that migrated into Papua New Guinea, Australia and the Andaman Islands...

would have also made it across

the Bering land bridge and into the Americas.

And they would've done so thousands of years before the second group.

- Exactly when this would have happened is unknown,

but this genetic signature is not present at all

amongst the indigenous populations of the people

descended from the Anzick child.

HARIDI: So there must have been at least two groups

and two separate periods of migration into the Americas.

And the ones who killed and ate these two mammoths

in the high desert of New Mexico

likely had distant relatives in Australia.

NARRATOR: As time progressed, this initial group was replaced

by a secondary one from Northeast Asia:

the one that has, to date,

been seen as the first to populate the Americas.

- When it comes to discoveries like this, we would be better served

by listening to the descendants of the people we are discussing

in order to obtain a fuller picture of long-ago events.

- This story is also an important reminder

that some of the theories we profess as absolute

aren't necessarily accurate,

and that we need to approach this topic, and, really, any topic,

with a healthy dose of humility and curiosity.

NARRATOR: Nabta Playa is situated 100km from the nearest settlement

of Abu Simbel, deep in the Egyptian desert.

Absent from its endless beige horizon are any signs of life.

Little stirs across the enormous, empty expanse of sand.

- This inhospitable landscape

receives as little as 1mm of rain a year.

It is crisscrossed by wadis.

These are dried-up ravines or riverbeds,

indicating that at some point, there was water here.

But now it is bone dry.

NARRATOR: While traversing the desert,

a Bedouin nomad came upon a mysterious collection of stones

scattered across the area.

- The megaliths lay at seemingly random intervals,

extending some 2.5km across the desert.

WEGNER: Megaliths are huge stone slabs

and wouldn't just appear in this environmental context.

So it's obvious that they were placed here with intent.

It would have required serious thought, and muscle,

to bring them all here.

- The Bedouin related what he had seen to the archaeologists

studying the region, and sure enough, with their curiosity piqued,

they arrived at Nabta Playa with the purpose of solving the mysteries

posed by the stones.

MIFFLIN: This is an incredibly hostile environment.

There is not enough water here to sustain the kind of work

needed to erect these massive stones.

So how could anyone have done this?

NARRATOR: Despite its current harsh conditions,

the presence of wadis indicate that, at some point,

water did flow through this area,

probably with enough volume to sustain plants, animals and humans.

- Throughout prehistory, megaliths were used singly,

or in groups, to create monuments, often to mark a site

with supernatural or spiritual significance,

or to indicate the location of a grave.

So the archaeologists suspect that some of them

could be sitting on top of one or several tombs.

- Digging into the ground reveals no human bodies,

however, initial excavations reveal ancient flora

that would require much more water than is currently available here.

NARDI: Finding organic matter like this

is extremely helpful for archaeologists.

It allows them to not only understand

what kind of environment would have existed here,

but also allows them to date the plants fairly accurately.

- Based on the plant species found during the excavations,

the area was probably receiving

anywhere from 30mm-200mm of rain a year

between 11,000 and 6,000 years ago.

This means that it was much wetter

and able to sustain life and human occupation.

NARRATOR: Annual monsoon rains arrived from the south,

creating seasonal lakes, otherwise known as playas,

that could sustain human and animal life for a few months a year.

The humid weather would have turned the area into grassland.

WEGNER: Underneath some of the megaliths,

the archaeologists do find bones.

But not human bones: instead, they find a bunch of cattle bones.

This is interesting, because in this region,

cattle are still a central part of existence.

NARRATOR: Cows provided wealth and status to those who owned them,

thereby forming an essential part of a hierarchical system

that has existed for thousands of years.

The more cows one had, the more status and power they attained.

- The Beja of the Eastern Egyptian Desert, for example,

are pastoralist people that use them not so much for meat

but as a constant source of sustenance,

obtaining milk from their bodies

to feed them in an otherwise barren, harsh environment.

NARRATOR: Thousands of years ago,

at the time the cattle bones were deposited,

it's possible people had a similar relationship to their cattle,

meaning they were valuable commodities that served spiritual,

political and practical purposes.

- It seems the creation of this site would have been done

by ancient pastoralists who held cattle as sacred.

NARRATOR: As the archaeologists continued to explore the area,

they uncovered 15 circular depressions

with the remains of cooking fires in the centre,

indicating that each depression was a separate dwelling.

- By dating the charcoal from the cooking fires,

they found that these houses weren't occupied simultaneously,

but at different periods, starting as far back as 9,000 years ago.

So could this have been an ancient village?

WEGNER: The houses are aligned along what used to be a water source.

So they had access to water.

And archaeologists also found a number of wells,

some up to 2.5m deep.

- So, beyond the unique circular formation,

we have evidence of cattle,

as well as the remains of several homes that had access to water.

So this was definitely a temporary village.

But what purpose would all these stones have served?

NARRATOR: As they continued their investigation,

the archaeologists found what appeared to be ten mounds

lined up against the western bank.

As they excavated them, they uncovered something

that left no doubt as to what this specific site was.

- There aren't human remains here either, but cattle, goats and sheep.

Most importantly, they find an entire young female cow skeleton,

which shows no signs of having been butchered or used for food.

- Considering how valuable these animals would have been,

could this be a sacrificial site?

NARRATOR: Archaeologists had discovered animal remains...

buried at the site of ancient rock megaliths,

in the middle of the arid Egyptian desert.

After finding the remains of a sacred cow, they were left to wonder

if they'd uncovered a place of sacrificial worship.

- The cow is found lying on its left side,

oriented with her head towards the south,

which, incidentally, is where the monsoon rains come from.

WEGNER: The cow's burial is in the wadi,

which, at the time, would have brought water into the playa.

So it was probably a good place to ask the gods for rain,

or thank the gods for having brought the rains in the first place.

NARRATOR: Radiocarbon dating of the plant matter

found in the cow's grave indicated that she'd lived

around 5270 BCE:

almost 7,000 years ago.

- Considering that the houses were around 9,000 years old,

this place must have seen continuous occupation for at least 2,000 years.

NARRATOR: Other than a seasonal village, this was an important site,

not just for practical reasons...

but for spiritual purposes as well.

It seems it could have been a holy site

for these ancient pastoralists moving through the desert.

- It would make sense that it carried religious significance.

It was a frequently and reliably watered place,

with feed for the cattle, and it would have stood in stark contrast

to some of the inhospitable surroundings.

ELLIS: There are a number of puzzling megaliths

marking the wider area, but on top of a small knoll,

there is a curious circle of stones half-buried in the sand.

It's made of upright, narrow slabs of stone,

and it looks like a gathering of tombstones.

The question is... what could this place be?

MIFFLIN: At first, they think this is a cromlech,

which is a circle of standing stones often used to indicate a tomb.

Yet there are no human remains found inside the circle.

WEGNER: So if it's not the site of a tomb,

stones placed in a circle like this

could also suggest a connection with celestial events.

A monument can be used to track changes in the sky,

whether as a sundial,

or a calendar used to track the movement of the stars,

or even indicate the arrival of the summer solstice.

ELLIS: Stonehenge in England is one such example.

We still don't know for certain,

but it is thought that this monument of megaliths

was used either as a celestial observatory,

like some sort of calendar,

or it could have been used as a religious site,

where rituals and ceremonies were conducted.

NARDI: Regardless of its specific use,

it was definitely tied to the heavens.

So could this stone circle be something similar?

If so, it would predate Stonehenge by thousands of years.

NARRATOR: Puzzled by what this could be,

an archaeoastronomy specialist was called in

to bring his expertise to bear upon these magnificent finds.

- Archaeoastronomy is the study of astronomical practices

in the ancient past,

meaning the study of how people used the heavens

in their respective mythology, folklore and religion.

- By knowing the age of the organic matter,

the specialist could then calculate when this circle of stones

would have aligned with the stars.

So they radiocarbon-dated samples of organic matter from fires

and from plant material found inside the circle.

NARRATOR: The research revealed that the stone circle

would have aligned with Arcturus,

Sirius and Alpha Centauri around 4800 BCE:

almost 7,000 years ago.

MIFFLIN: This is really fascinating.

Arcturus is one of the five brightest stars in the night sky.

Sirius is the brightest,

and Alpha Centauri is the fourth-brightest.

NARDI: He quickly realised that all the megaliths

were a part of a greater structure.

All the stone constructions across the entire area

were interrelated, including the stone arrangement.

ELLIS: So, like Stonehenge, this, too, is likely an ancient sundial.

It was found in a wadi, which, at the time,

would have been partially submerged in water for a few months a year.

NARRATOR: Two of the stone pairs in the circle

align along an east-west axis.

They're calculated to have been in line

with where the sun would have risen and set during the summer solstice.

The stone circle was a means by which these people observed,

and marked, changes in the celestial night sky.

At the time, one could see

the reflection of the stars in the water, and in turn,

see how the stones lined up with those very stars.

- For these ancient, semi-nomadic people,

the stars would not only have been a place where the gods resided,

but also the means by which they navigated,

and survived, in the desert.

NARRATOR: Nabta Playa was an ancient gathering place

where people came from far and wide to observe the stars,

pray for rain, and welcome the summer solstice,

which would then mark the start of the annual monsoon.

It's one of the earliest pieces of evidence we have

of celestial observation,

and reflects an incredibly sophisticated understanding...

of both time and space.

- Sometime between 5000 BCE and 3000 BCE,

the climate changed, and the area dried up.

Nabta Playa was abandoned and fell victim to time,

slowly being buried by the shifting sands of the desert.

Since its discovery, the Egyptian authorities have gone through

the painstaking process of moving the stones to a safe site

and replicating their alignment

in order to preserve it for future generations.

Subtitles by Sky Access Services