Original subtitles

[dramatic music]

- [Narrator] We are surrounded

by extraordinary feats of engineering.

Constantly pushing the boundaries of what's possible.

- Without engineering, there'd be no modern world.

- [Narrator] Gigantic cities.

Amazing infrastructure.

And ingenious inventions.

- Engineering is the key to turn dreams into reality.

- [Narrator] To reach these dizzying heights.

Today's technology relies

on breakthroughs made by ancient engineers.

- It's mind boggling how they did this.

- [Narrator] How did early civilizations build

on such a scale?

- They raised the bar for construction in a way

that no one thought possible.

- The sheer engineering ability

that is in itself impressive.

- [Narrator] By defying the known laws of physics

and daring to dream big. [dramatic music]

They constructed wonders of the world,

from gigantic pyramids

to awe-inspiring temples

and mighty fortresses.

All with the simplest of tools.

- Cannot imagine the skills people would have needed

to build like this.

- [Narrator] Now it's possible

to unearth the secrets of the first engineers.

- They managed to construct edifices

that have survived the ravages of time.

- [Narrator] And reveal how

their genius laid the foundations

for everything we build today.

[dramatic music]

In every corner of the earth,

humans have created huge monuments

carved from a material capable

of withstanding the test of time.

Stone.

[dramatic music]

- Our ancestors certainly understood the timelessness

and the monumental qualities of stone.

- [Narrator] Extremely hard wearing

and found almost everywhere.

Stone can also be a thing of beauty.

[dramatic music]

These attributes have made it the construction material

of choice throughout history.

Used in engineering marvels built to mark great victories,

to celebrate national values, or to honor heroes.

- People have come together to build monuments

to celebrate, to have a place to gather, to mourn the dead.

[dramatic music]

- They say a lot about how society sees itself,

but more importantly, they say a lot about how

a society would like other people to see them.

[dramatic music]

- [Narrator] Iconic recent examples include the monuments

of Washington, DC.

The National Mall is a series

of spectacular buildings and structures.

A sacred complex in the center of the capital city.

- Washington, DC is the beating heart of America.

And the National Mall is the beating heart of Washington.

- [Narrator] This is the setting

for great moments in America's national story.

- It's a stage for American democracy.

It's where the people

of America can come to have their own voice.

[dramatic music]

- [Narrator] Each of the mall's structures

is an engineering triumph in its own right.

The Washington Monument, a towering 555-foot obelisk.

The world's tallest stone structure.

[dramatic music]

- The Washington Monument is a very simple structure.

It's just marble blocks stacked on top of each other.

It doesn't use mortar and it doesn't use reinforcing steel.

So it has to be made to very fine tolerances

so the blocks sit together.

[dramatic music]

- [Narrator] There's also the Lincoln Memorial,

the Vietnam Veterans Memorial, and the Jefferson Memorial.

The entire complex has been precision engineered

to be geometrically aligned. [dramatic music]

- The monuments are laid out in a way

that you're able to see and get get these great vistas

from multiple different directions.

[suspenseful music]

- [Narrator] These stone monuments were built to last,

using precision engineering.

But they incorporate lessons learned

from ancient engineers whose earliest structures

still standing today were built back in the Stone Age.

[suspenseful music]

[wind whooshing]

[suspenseful music]

Stone monuments date

from the very dawn of civilization.

In the prehistoric period before written records began.

- Stone monuments aren't new.

They're something that's been going on since 9,500 BC.

- [Narrator] This period known

as the Stone Age produced monuments that still stand today.

[suspenseful music]

With individual components reaching as high as 30 feet

and weighing up to 25 tons.

Some are engineering enigmas.

- You cannot stand there

without questioning how it was achieved.

- [Narrator] Remarkably, ancient engineers constructed

these monuments before the invention of metal tools

or even the wheel. [dramatic music]

- We're looking at substantial amounts of labor.

And that is something that is just unmatched.

- [Narrator] Their origins

have long been shrouded in mystery.

Little is known about the people who built these structures

and to what purpose, but science is now starting

to unlock the engineering secrets of these ancient wonders.

[dramatic music]

[suspenseful music]

One of the earliest at greatest prehistoric monuments

is found on the wild coast of Brittany, Northwest France.

Carnac.

The monument dates from around 4,500 BC

in the Neolithic or Late Stone Age.

- Carnac is one of the great wonders of the Neolithic world.

- [Narrator] It's thought to be the oldest

of Europe's stone megaliths.

Over the course of a millennia,

Stone Age people, believed to be hunter gatherers,

place an extraordinary 10,000 stones upright

in the ground at Carnac.

- Carnac is one of a number of stone rows

that we find in Brittany from that prehistoric time.

It's simply the grandest, the biggest,

and the most elaborate. [dramatic music]

- [Narrator] Spanning a total area

of over five square miles.

It's also the largest collection

of megalithic standing stones anywhere in the world.

They're laid out in long parallel rows

and in strange semicircular arrangements.

- The big, distinguishing feature of Carnac is

that it has huge alignments

of standing stones.

Six, eight abreast,

marching across hundreds and hundreds of meters,

turning corners and so on. [dramatic music]

- [Narrator] It's still unknown exactly

how ancient engineers planned this monument.

But there's no doubt it was a challenge.

Carnac is built on a vast scale.

This has helped give rise

to some extraordinary notions over the centuries.

- One of the most common myths and legends

that we have associated with our stone circles

and our standing stones is

that these are petrified people.

People who are petrified

where they were performing their ceremonies and rituals.

- [Narrator] While it's likely Carnac

was built for ritual purposes,

nothing is known of the actual rites

that may once have been performed here.

[dramatic music]

Some have even speculated

that Carnac could be a kind of astronomical calendar.

But built long before any written language,

there's little evidence for this.

In fact, the only remnants from the Stone Age

are the stones themselves.

[dramatic music]

Ranging from three to 20 feet in height.

Many are formed of solid granite,

quarried from the local area.

This rock is an extremely tough material.

It's a mystery as to how Stone Age hunter-gatherers

had the engineering ability to shape these blocks.

[peaceful music]

But there is evidence of some

even more complex engineering dotted

around the Carnac site.

[suspenseful music]

Dolmens.

These are thought to have been covered mounds

when originally constructed

and at least 50 are spread out across the area.

- The dolmens tend to be monuments

where a large capstone,

sometimes upwards of sort of 40, 50 tons is raised up

on other upright stones in order to create a chamber.

- [Narrator] The design is substantial,

with heavy supporting blocks topped by a massive capstone.

- Just the engineering of actually producing one

of these is quite phenomenal.

It's kind of

like building Stonehenge times 10 I think sometimes.

[suspenseful music]

- [Narrator] Maneuvering these stones into position

would have required engineering know-how and planning.

One theory is that the huge capstones weren't moved at all,

but were already in situ.

[dramatic music]

- The stones from Carnac were most likely gathered

in the locality.

A scenario that is strewn

with granite boulders and other forms

of other nice shaped stones.

So they had the ideal resources immediately to hand.

[dramatic music]

- [Narrator] Ingenious neolithic engineers

would then have tunneled beneath each side,

before sliding smaller supporting stones into position.

- Just the way that it's constructed is amazing.

You would have these standing stones

to create, I suppose, the walls.

So that would then be the foundation for the outer chamber.

And also the capping.

[suspenseful music]

- [Narrator] Tunnels were then dug into the structure

and a chamber excavated beneath the capstone.

It's believed they may have been collective tombs.

Although, in the acidic soils of Brittany,

no trace of human remains has survived.

[suspenseful music]

Their true purpose may never be known.

There's no doubt

that excavating these chambers was backbreaking work

with the limited tools available.

But some of the basic principles pioneered

in Stone Age France have evolved

into engineering techniques used today.

[dramatic music]

[wind whooshing]

[upbeat music]

Even in the modern era, tunneling can be a daunting task.

[machinery clanking]

It's a construction process that's still essential.

Though today, transport,

rather than tombs, are the priority.

The best place to put a railway

in a crowded modern city is in a tunnel below the ground.

But that's not straightforward.

- The big challenge of building underground railways

is how do you make the hole.

To try and create tunnels

underneath cities is hugely challenging.

- [Narrator] The first underground railways

were built using a technique known as cut and cover.

- You literally cut a hole,

a sort of a ravine into the ground.

Put brick sides on it.

And then you cover it again

once you've got the tunnel underneath.

[upbeat music]

- [Narrator] But this approach

caused disruption above ground.

Sometimes meaning entire buildings had to be demolished.

[explosion booms]

So engineers developed a technological wonder.

A machine for boring out tunnels.

Also known as the mole.

- The great innovation in tunneling was the invention

of the tunnel-boring machine.

Basically it's a shield that allows you to dig away

at the front while protected from the ground collapsing

on top of you

- [Narrator] The subterranean monsters

reach almost 300 feet in length.

Weight over 6,000 tons,

and exert a monstrous 25,000 brake horsepower.

Hydraulic jacks generate forward thrust

while a rotating cutter head claws the material

from the tunnel face.

It can dig through either earth or solid rock

and a conveyor belt shifts the loosened material

to the back of the machine.

In this way, the mole cuts

over 230 feet of tunnel in a single day.

And best of all,

these machines have little impact on the surface.

- The great benefit of the tunnel-boring machine is

that the people above basically don't know you're there.

Life can carry on above as if nothing is happening.

[upbeat music]

[machinery whirring]

[stone rattling]

[suspenseful music]

- [Narrator] In the Stone Age,

such equipment would have seemed like some form of magic.

But despite their rudimentary technology,

prehistoric builders managed to create engineering marvels.

One remarkable monument lies over 400 miles

across the ocean from Carnac in Ireland.

Newgrange.

Built around 1000 years after the construction of Carnac,

it's evidence of a huge stride forwards in engineering.

[suspenseful music]

- Newgrange is a passage tomb on the east coast of Ireland.

It's a monument that was built round about 3000 BC.

So now we're talking about the Middle Neolithic period

and it's a tomb that was incredibly sophisticated.

It's huge.

- [Narrator] This is a burial chamber far bigger

than those that had gone before.

[suspenseful music]

In total, it's made up of around 200,000 tons of rock.

To construct the inner chamber,

ancient engineers used a technique known as corbeling.

Overlapping stones that gradually narrow as they rise

until a capstone can be placed on top.

[dramatic music] At 270 feet in diameter,

43 feet high, with a 62-foot chamber concealed inside,

this is a truly enormous structure.

Some experts believe this was a major ritual center,

but others argue it was more straightforwardly

a burial place.

- It's one of the largest passage tombs in Ireland.

And it was used, we think, for the burial of the dead.

Mostly cremations. [dramatic music]

- [Narrator] Not all archeologists agree

that Newgrange was a tomb.

Though fragments of bone have been discovered

in the passage way.

Remains of possible grave goods have also been found.

But Newgrange's greatest engineering secret

was only revealed in the 1960s.

Archeologists identified a curious decorated structure

above the tomb entrance.

They named it the roof box

and realized it had been designed

for a very specific purpose. [dramatic music]

[suspenseful music]

Ancient engineers constructed the passageway leading

into the tomb with great accuracy.

To channel light from the roof box

on the first sunrise after the winter solstice.

- The light of the sun just after it rose

around winter solstice would have shone right into the tomb

and lit up the bones of the dead inside.

[dramatic music]

- [Narrator] The floor of the passage was designed

with a gradual slope.

So light from the box could reach right

into the inner chamber on this day.

It's an impressive piece of precision engineering,

built into such a huge and ancient structure.

What it tells us is

that there was some connection going on in people's minds

between death, ancestors', ancestor spirits,

on the one hand.

And the sun, seasonality, seasonal renewal on the other.

- In order to build a monument

that aligns with the sun,

you need to have observed the movements of the sun

over at least a year's period.

- [Narrator] This discovery proves

that Neolithic humans were becoming skilled engineers.

Pre-planning their projects to yield extraordinary results.

[suspenseful music]

It's also evidence of prehistoric knowledge

and understanding of the sky above.

And the birth of astronomy.

[wind whooshes]

[stone rattling]

[suspenseful music]

Monuments throughout the ancient world share alignments

with solar and celestial objects.

Sun, moon, and certain stars.

From Uxmal in Mexico

to Egypt's Great Pyramid and Chaco Canyon

in the Southwest United States.

The reasons why this was done remain shrouded in mystery.

Ancient people may have used astronomy to create calendars.

Important for the agricultural season.

[suspenseful music]

Other reasons could have been more mythological.

Long-forgotten ancient beliefs and rituals.

Whatever the purpose, early people went to great lengths

to engineer their monuments to reflect celestial events.

- The sun and stars have been

so important to humans for millennia.

- [Narrator] Humanity's fascination

with the sun and stars hasn't diminished in the modern era.

But while Stone Age people could only observe the night sky

with the naked eye, subsequent engineering developments

have led to vastly superior tools.

The greatest breakthrough came with the invention

of the telescope in 1608.

Cue the renowned astronomer, physicist,

and engineer Galileo Galilei. [suspenseful music]

- Galileo's telescope refracts light.

So it bends light.

And that's what gives it the magnification.

- [Narrator] Galileo refined telescope technology,

improving magnification from three times

to 20 times that of the human eye.

With these devices, he observed the craters of the moon.

Saturn's rings.

Sunspots.

And Jupiter's moons.

Today's telescope engineers continue to push the envelope,

making it possible to peer ever further into deep space.

[suspenseful music]

- The engineers play a key role

in increasing the understanding of the universe.

And one of the ways they do that is working on telescopes.

- [Narrator] The South African Large Telescope,

built in the desert of Karoo,

is one of the biggest in the world.

Its huge hexagonal primary mirror array measures

over 30 feet across

and contains 91 individual

three-foot-wide hexagonal mirrors.

But no matter how large a telescope becomes,

Earth's atmosphere and shifting air pockets

will always distort light, limiting observations.

Engineers once again came up with a solution.

Put a telescope in space. [suspenseful music]

- The Hubble Space Telescope has been one

of the greatest things we've ever done in space.

- The Hubble telescope is very big.

I mean, it's the size of a school bus

and it weighs several tons and it presents a huge challenge

getting something of that size into space.

- [Announcer] Four, three, two, one.

And liftoff! [rocket whooshing]

- [Narrator] Hubble was assembled on earth before

being launched into orbit on board the Challenger Shuttle.

From space, without the atmosphere blurring its view,

the telescope has captured some

of the clearest, most detailed images

of the universe ever seen. [suspenseful music]

[wind whooshing] [stones rattling]

Prehistoric astronomy was limited in comparison

to modern-day space exploration.

But Stone Age people weren't the thuggish caveman

they're sometimes thought to be.

[suspenseful music]

Some of the engineering achievements they've left behind

provide evidence of a highly complex way of life.

- I think people think

that prehistoric people are really unsophisticated,

but I think that's really far from the truth.

You have these very complicated,

intelligent, community-based societies.

- [Narrator] One of the best spots to see this is Orkney.

Off the Northern tip of Scotland.

It's a storm-lashed place of rugged cliffs.

Today it seems a remote part of the world

on the very edge of the map.

But 5,000 years ago, Orkney lay

at the center of trading routes, running all the way

to Europe via the North Sea. [suspenseful music]

And the Stone Age people living on these islands

were taking great strides in ancient engineering.

- 5,000 years ago, Orkney was an astonishing center

of innovation and invention.

It's like the Silicon Valley of the Neolithic.

[dramatic music]

[suspenseful music]

- [Narrator] One intriguing site was revealed back in 1850

when a great storm stripped grass

and earth from a large mound. [suspenseful music]

It exposed the outline of some substantial stone structures.

Excavation showed them to be a series

of interconnected houses.

At first, nobody was sure quite how old they were

but radiocarbon dating proved

they'd been built in the late Stone Age.

- The structures in Orkney were unlike anything else

in the British Isles.

They were very, very complex and beautifully made.

[suspenseful music]

- [Narrator] This site, known as Skara Brae, is evidence

that prehistoric homes were far more advanced

than had been thought.

- Skara Brae tells us an awful lot about the settlements

of these people because it's built out of stone

and we can see all the detail of what's going on it.

[suspenseful music]

- [Narrator] It's thought that approximately 50 people

would have lived in the houses.

Finds include jewelry, needles, dice, and buttons.

But no weapons have ever been discovered,

suggesting these were peaceful farming people.

They must, at some point,

have migrated here from the mainland.

Remarkably, their 5,000 year old homes were constructed

with many of the creature comforts enjoyed today.

[suspenseful music]

- Archeologists have found the bed boxes,

the little dressers.

The hearths, boxes set into the floor for storage of food.

- [Narrator] Incredibly, the houses of Skara Brae

were built without the use of mortar or cement.

Their walls have an inner and outer layer of stone,

thought to be filled with some form of insulation.

And these homes are just one

of several remarkable prehistoric monuments on Orkney.

Nearby, the tomb of Maeshowe.

Just like Newgrange,

its entrance passage is carefully engineered

to align to the winter solstice sun.

[dramatic music]

There's also the spectacular Ring of Brodgar.

Measuring over 300 feet in diameter,

with stones up to 15 feet tall.

Only 27 of the original 60 stones remain standing today.

But their size is testament to the skill

of Orkney's ancient engineers. [peaceful music]

[wind whooshing]

[stone creaking]

[upbeat music]

In the modern world,

architects are still drawn to the circular form.

- The circle represents a number of things to humans.

It could be unity, focus, infinity, inclusion.

It's a very powerful symbol.

- One of the best known examples

of circular buildings is Apple Park

in Cupertino, California.

Designed by Sir Norman Foster,

this is the super high tech headquarters

of the vast multinational.

- The Apple building is a perfect circle.

Apple co-founder, Steve Jobs,

wanted his office building obviously to stand out,

to be unique, but also he wanted it

to not feel like an office space.

To have that innovative feel

and allow people to really think outside the box.

- [Narrator] The structure forms a perfect ring

a mile in circumference. [upbeat music]

but ring shaped or circular designs

can give rise to complex engineering problems.

- Circular geometries present challenges

for modern construction.

Most of the stuff we make is flat

or straight or right angled.

- [Narrator] 3000 curved panes of glass

were custom engineered for Apple's HQ.

At 49 feet tall,

these are the largest curved glass panels in the world.

Luckily, with so much glass,

the building is earthquake proof.

It uses base isolation technology to reduce shaking.

The entire structure resting

on 692 huge stainless steel saucers.

It can move as much as four feet in any direction.

This is one

of the reasons Apple Park is thought

to have cost around $5 billion to build.

The immense, light-filled glass circle

has already become an engineering icon

of the digital era.

[wind whooshing]

[stone rattling]

[suspenseful music]

But a very different circular structure is hailed

as the greatest engineering icon

of the prehistoric period.

A mysterious and complex monument dating

from around 3000 BC. [suspenseful music]

Stonehenge.

[dramatic music]

- Stonehenge is an icon of prehistory.

- When you stand and look at these incredible stones,

you can only feel awe and wonder.

[dramatic music]

- [Narrator] The monument makes striking use

of enormous stone blocks.

Some as tall as 30 feet.

Weighing up to 25 tons.

[dramatic music]

- The construction of Stonehenge

is an astonishing achievement.

It's amazing that they even conceived of the idea,

let alone actually managed to build it.

- [Narrator] Before the arrival of paved roads

or even the wheel to Britain,

this was a major feat of engineering.

[dramatic music]

- It's something that happened

over a very, very long period.

It roughly took about a thousand years

to create this huge monument. [dramatic music]

- [Narrator] Exactly how did ancient engineers

pull off the seemingly impossible?

[suspenseful music]

First step was to identify a site.

And Salisbury Plain had obvious advantages.

The high, open area was the ideal spot

for a striking monument.

It would be visible for many miles around.

[suspenseful music]

- We know that the Salisbury Plain area

was this chalk upland

where potentially not as many trees were growing,

as in other parts of Southern England.

[suspenseful music]

- [Narrator] The first stage in the construction

of Stonehenge occurred around 3000 BC

when ancient engineers dug a huge circular ditch

and raised bank.

[suspenseful music]

- Actually creating that was quite a big deal.

It's just the amount of man hours.

- [Narrator] The bank at Stonehenge forms a massive circle

over 350 feet in diameter.

And the ditch itself is wide and deep.

It was cut into tough, chalky soil

without the benefit of modern digging equipment.

- These people don't have a JCB.

They don't have shovels.

They don't have mattocks.

- [Narrator] Archeological finds

from across the site provide clues to how it was done.

Antlers.

Deer antlers are formed of tough bone

with sharp points making them ideal

for cutting into chunky ground.

- It is quite an astonishing feat

that people managed to dig out chalk

using simple antler picks.

- [Narrator] But this still wouldn't have been an easy task.

It's estimated that excavation

of the ditch alone could have taken a workforce

of up to 4,000 people several months to complete.

Recent finds suggest that workers lived nearby

in a settlement known as Durrington Walls.

Over 1000 dwellings have been identified here

and it's believed people may have come

from far and wide to help.

[dramatic music]

[stone rattling]

[suspenseful music]

It's not known exactly when Stonehenge got its first stones,

but many were in place by 2,500 BC.

Two main types were used.

Smaller bluestones and the larger sarsen stones.

- The bluestones at Stonehenge represent

the first significant stone works to be erected on the site.

Before then, it was earthen works.

- [Narrator] Only in 2015 were scientists finally

able to pinpoint exactly where the bluestones originated.

- Geologists have managed to chemically match them

to the Preseli Hills.

- [Narrator] The Preselis lie in West Wales,

over 140 miles from Stonehenge.

[suspenseful music]

And the unique geology here makes

this the only possible source of stone in Britain

for the Stonehenge bluestones.

- The bluestones themselves look very distinctive.

They're this very dark gray-blue color.

And most of them have this quartz fleck in them.

[suspenseful music]

- [Narrator] But how did ancient engineers extract

the massive four-ton blocks?

The recent discovery

of the original Stonehenge quarrying site

offered archeologists vital clues.

- What they have noticed is that there's

these huge fissures in the rocks.

And they're actually taking advantage

of these cleaving points.

[dramatic music]

- [Narrator] Analysis shows that neolithic engineers

likely hammered large wedges into the many cracks running

along the top of the pillars.

- They were probably using wooden wedges

which they could make wet and expand

to ease out and lever the stone.

- [Narrator] As the wedges expanded,

they'd split the stone,

enabling huge slams to be prised away from the quarry face.

And this same basic quarrying method

has been in use ever since.

[gears rattling] [suspenseful music]

Even in the 21st century

- People doing quarrying will try

and find the fissures, recognizing

that that's where the weaknesses are.

- [Narrator] But in the modern world,

quarrying has evolved.

[explosions booming] [intense music]

The introduction of explosives in the late 19th century

changed the face of this industry.

Explosives detonate to produce powerful blast waves

and large volumes of gas.

Because they're confined in a hole,

the expanding gases are forced into existing cracks

and create new ones to break the rock apart.

[explosion booms]

Mining engineers still use blasting today

but explosives can be inefficient,

pulverizing valuable material along with unwanted spoil.

So more precise techniques have also been developed.

[suspenseful music]

Crucially the use of helicoidal wire.

- So they use helicoidal wire saws in quarries

as a way of cutting

through relatively soft rock like marble.

- It's essentially three wires

that are wound round each other

that you can accurately cut through stone.

By creating a loop of this wire

that is driven around the stone

and gradually cuts through it

with some kind of lubricant to cool it down.

[upbeat music]

- [Narrator] The wire moves at speeds

of close to 50 feet per second.

Sometimes embedded with diamond dust for extra bite.

- You can get very neat cut and so it comes out

and needs relatively little work to be usable afterwards.

[upbeat music]

- [Narrator] Once cut, diggers push huge slabs

of stone free with little wastage.

Thanks to this technique, the world famous Carrara quarry

in Italy produces an incredible 1 million tons

of marble per year.

But modern quarrying

can also have a major environmental impact.

Some scientists blame it for ground water pollution,

noise and air pollution, and a loss of biodiversity.

[machinery rumbling]

[gears clacking]

[suspenseful music]

In prehistoric Britain,

the extraction of the bluestones

in South Wales using natural fissures

was a stroke of genius.

But for centuries, historians have struggled

to understand how engineers transported the four-ton stones

over 140 miles to Salisbury plain.

[suspenseful music]

- The bluestones must've meant something more

than just practical reasons.

Otherwise you wouldn't bring them over 200 miles.

- [Narrator] In early 2021,

new evidence appeared to provide an answer.

Archeology showed that,

long before Stonehenge was built in England,

the bluestones had first been erected

as a stone circle in Wales.

Close to the quarrying site. [suspenseful music]

- It may be that the people who built Stonehenge saw

the Preseli Hills as their ancestral home.

It may be that that was a particularly sacred place.

These mountains were special places.

Places of the gods.

- [Narrator] Centuries later,

this original circle was dismantled.

- The current theory is that when the monument

was then dismantled

that they were then transported and reused in Stonehenge.

- [Narrator] Whatever the circumstances,

transporting the stones was a mammoth undertaking.

And a huge engineering challenge.

In an age before road networks,

sea transport seems

to have been the obvious way of moving them.

[suspenseful music]

- We've assumed in the past that the easiest way

to move one of these bluestones would be

to get it down to the coast,

put it on some kind of neolithic boat or raft.

- You would have gone

down the Pembrokeshire coast into the Bristol Channel.

- [Narrator] This route would have involved

ferrying the stones across the channel,

leaving just a short distance to cover by land

before reaching Salisbury Plain.

But experimental archeology

has highlighted the dangers involved.

[suspenseful music] - Back in 2000,

a Millennium grant was given to a team to try just that.

It didn't go well.

They'd only got half a mile out to sea

at Milford Haven when the thing sank.

[water whooshing]

[suspenseful music]

- [Narrator] In 2012, a second attempt

proved more successful.

But it seems unlikely

that the stones were transported all the way by sea.

Many miles of the bluestones' journey to Salisbury Plain

must've been by land, across a variety of terrain.

[peaceful music]

- It would have had to be a massive group effort.

Yes, you can do it.

But I think the scale of that

and the organization level would have been huge.

[suspenseful music]

- [Narrator] To understand how it may have been done,

students from University College London carried out

some experimental archeology.

Attempting to become megalith movers.

Previously, many experts thought log rollers were used.

But the team believed a different approach was more likely.

They used a cradle to hold the stone

and attempted to slide this load along the track way.

- They were building a short stretch

of timber track way and experimenting

with the stone that was attached to a cradle over that.

And they were really surprised by how easy it was.

[suspenseful music]

- The experiment showed that groups

of just 10 people could move a large stone.

Far fewer than experts had predicted.

However, vast numbers of workers would still

have been needed.

Perhaps over 3000 at any given time.

- That level of organization is quite phenomenal.

Just to think about it.

You would have to have organized teams,

almost like a relay race.

[people cheering]

[suspenseful music]

- [Narrator] The successful delivery of the bluestones

to Salisbury Plain was a great achievement.

But Stonehenge was far from the only stone circle built

in this period.

They were constructed all across Europe

in the Neolithic era.

Surviving to this day at sites

such as the Gulf of Morbihan in France, Avebury in England,

and Almendres Cromlech in Portugal.

Some archeologists believe they were built

as temples or ritual gathering places.

Whatever the purpose of these monuments,

there's no doubt that Stonehenge continued

to grow in importance.

[dramatic music]

[stone rattling]

[suspenseful music]

The next major phase of construction

at the site took place towards the end

of Britain's Stone Age.

And made the monument into the famous shape

that's still visible today.

To achieve it, eight additional features would be added.

Among them, the five world famous trilithons.

Groups of two uprights sarsen stones

with a third set horizontally across the top.

They're the largest of all the Stonehenge stones,

weighing up to 30 tons a piece.

- When the huge stones arrived,

that was the time when Stonehenge became

something completely unique.

Unimaginable effort was put

into those incredible feats of engineering.

- [Narrator] Unlike the bluestones,

the massive sarsens seem to have been found close to hand.

- Recently there's been research

with geochemical techniques on these stones

and sourced the exact location of them.

A place called the West Woods.

[dramatic music]

- [Narrator] West Woods lie on the Marlborough Downs,

just 15 miles from the Stonehenge site.

It's thought that another trackway was built

to move the sarsen blocks.

Probably taking several years to construct.

For prehistoric people, transporting stones on the scale

was a truly awesome feat of engineering.

- For them, this would have been like the moonshot.

The most amazing thing that ever happened

to create a wonderful structure.

[dramatic music]

[wind whooshing]

[stones rumbling]

[suspenseful music]

- [Narrator] 4,500 years later,

preparing for the actual moonshot.

NASA engineers also face the daunting challenge

of moving a gigantic load.

One that dwarves Stonehenge.

The Saturn V.

[upbeat music]

The largest rocket ever built.

Weighing over 6 million pounds,

it's as tall as a 36-story building.

Simply moving this monster

to the launch pad was an engineering feat

in its own right. [upbeat music]

Technicians had

to design a gigantic new vehicle to do it.

The crawler-transporter.

- It's this incredible machine.

It's got these huge caterpillar tracks

and then a self leveling top.

That means that it can carry the Saturn V rocket

whilst keeping it steady.

- [Narrator] The transporter

is actually the largest self-powered land vehicle

in the world.

131 feet long, weighing over 2,500 tons,

and costing $14 million.

It even uses laser guidance to ensure perfect accuracy

when docking at the launch pad.

The combined weight of rocket

and transporter would have damaged ordinary roadways.

- NASA had to create essentially an airport runway

for this vehicle to travel on.

It couldn't travel on normal roads.

- [Narrator] Engineers built

a heavily reinforced crawler way.

Two 40-foot wide lanes, just over four miles long.

It was constructed with a layer of Alabama river rock.

Up to eight inches thick.

Sitting atop four feet of graded, crushed stone.

On this solid base, the Apollo rockets took

their first careful steps

on the long journey to the moon.

[rocket whooshing]

[wind whooshing] [rocks rumbling]

[suspenseful music]

The completion of Stonehenge in around 2200 BC marked

the end of Stone Age Britain and the dawn of the Bronze Age.

Over the next few centuries, metal tools were used

to make carvings on the stones,

no longer visible to the naked eye.

But there's one final engineering secret

built into the fabric of Stonehenge

that lay hidden until the 18th century.

[suspenseful music]

The monument is perfectly aligned

with summer and winter solstices.

- Stonehenge is very carefully constructed

so that sunrise on midsummer's morning,

the shafts of light comes straight down the solar axis,

right next to something called the Heel Stone,

which is the largest stone in Stonehenge.

[suspenseful music]

- [Narrator] A two-mile-long formal approach

to the monument is perfectly aligned with both solstices.

On Midsummer's Day, the sun rises over the outer Heel Stone

and is beautifully framed by the upright sarsens.

Prehistoric engineers must've carefully observed

and charted the skies to make such an alignment possible.

Further evidence of their sophistication.

[suspenseful music]

- It's the notion of how intelligent people were back then.

How in touch they were with nature.

How much that they understood their surroundings.

[suspenseful music]

- [Narrator] Knowledge of the sun

was vital for early farmers.

And some have argued this is one reason

behind the monument's construction.

It may also have been a gathering place

or temple for those celebrating the solstice.

- They may have had religious beliefs

that met that during the longest night of the year,

you had to perform certain ceremonies and prayers

and incantations to make sure the sun came back.

[dramatic music]

- [Narrator] Even today, as many as 10,000 people come

to Stonehenge to watch the magic moment planned

by ancient engineers.

[dramatic music]

Before written history began,

prehistoric people left their mark on the planet.

The Stone Age monuments still standing today prove

that ancient humans were sophisticated,

highly skilled, intelligent.

From Skara Brae to the Newgrange Tomb,

engineering principles were shared and enhanced.

Culminating in the wonder of Stonehenge.

To this day,

these ancient monuments mesmerize millions.

Reminders the triumphs of the first ancient engineers.

[dramatic music]