Original subtitles

(dramatic music)

- [Narrator] The world's greatest structures

push the boundaries of engineering

all fueled by a constant desire to innovate.

- Without engineering, there will be no modern world.

- [Narrator] Gigantic buildings, complex infrastructure

and ingenious inventions.

- Engineering is the key that turns dreams into reality.

- [Narrator] Many of today's incredible achievements

rely on breakthrough technologies

first devised by ancient engineers.

- It's astounding how they achieved this.

- [Narrator] Early civilizations

built on an unimaginable scale

and with incredible precision.

- They raised the bar for engineering

in a way that no one thought possible.

- These are some of the finest engineers in history.

- [Narrator] Redefining the known laws of physics

and dreaming up the impossible.

They constructed engineering wonders from colossal stadiums

to mighty waterways and complex machines,

all with the simplest of tools.

- You cannot imagine the skills people would've needed

to build like this.

- [Narrator] By unearthing the mysteries

left by these ancient engineers,

we can now decode their secrets.

- That so many of their creations still survive

is testament to their engineering prowess.

- [Narrator] And ultimately reveal how their genius

laid the foundations for everything we build today.

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Of all the structures on the planet today,

few are as awe inspiring as bridges.

- I think people relate to them. They do something to us.

They talk about human ingenuity.

- They're almost impossible things.

They span enormous natural features.

They get lost in the mist.

- [Narrator] With the longest over 100 miles in length

and some reaching heights of more than 1000 feet

spanning rivers, seas and even continents.

They are the structural giants of the modern world.

- Many of the world's great cities have founded by water

and very often, bridges are the grandest structures

of those cities.

- Bridges are so important cause they actually capture

the scale and the skill at any point in history.

- [Narrator] In the modern age,

bridges have had to bear ever increasing loads of traffic

and remain essential for travel, communication and commerce.

- Bridges are our critical connectors of society.

They really are the lifeblood of our transport system.

- [Narrator] But they are more than just conduits

of our global economy.

When it comes to human creativity and ingenuity,

little can compare with the inspired variation

that goes into building bridges.

From the Helix Bridge in Singapore

which mirrors our body's DNA

to Vietnam's Golden Bridge held up by faux stone hands

or the distinctive configuration

of the gates at Millennium Bridge

which spans the river Thyme in England.

- It's unique in the way that it moves

which is really unusual and it's terribly clever.

- [Narrator] But innovation in bridge design and engineering

goes as far back as our first human ancestors.

(light music)

Ever since early humans first walked the Earth,

we've needed to find ways to span gorges, rivers

or sometimes just the smallest of obstacles.

- It's entirely possible that the first bridge builders

were people in the Neolithic period

because at that point, they've got stone tools

and with those stone tools, they can fell trees.

- Those early humans put in that first log across the river

where if you like the kind of very first engineers.

They had a problem and they find a solution.

In a way that was the birth of engineering.

(light music)

- [Narrator] For thousands of years,

humans assembled rudimentary bridges.

But around 4,000 BC,

as farming settlements became established

across Northern Europe,

communities needed more reliable methods to cross waterways

or natural barriers.

- As early humans began to explore their environment,

they were seeking ways to bend nature to their will.

And one of the ways of doing that

was to make a quick route from A to B.

- [Narrator] For the ancient engineers

of the Somerset Levels in Southwest England,

the challenge was how to cross the low marshy peatlands

to reach their agricultural and foraging grounds.

- This is a wetland landscape which most of the year

is damp and boggy,

but sometimes is almost completely covered by water.

So not only is it difficult to traverse,

to actually build something in this landscape,

is equally challenging.

- In some ways it's the most difficult kind of thing

to bridge over

because you've got nothing to stand on.

You can only build out from one end

and you can stand on the thing that you've already built

to build the bit in front of you.

- [Narrator] The other key challenge they faced

was how to reliably support any kind of structure.

- The obvious solution was to introduce some form

of vertical pile.

But the problem is that piles will sink into the mud.

So another solution had to be found.

- [Narrator] In the 1970s,

archeologists determined exactly how they solved this issue.

Preserved in the peat was a raised wooden track

acting as a low bridge to cross the marsh

which has been dated to 3,806 BC.

- This track is over a mile long.

So this is significantly big bit of infrastructure

that would've taken thought and planning and organization.

- [Narrator] The result

was a design that would raise these farmers

above the marsh,

allowing them to cross much more easily and reliably.

- They came up with a design which featured crossed stakes

driven into the mud

which supported a series of wooden platforms.

- By inclining those wooden pegs into the ground,

it forms a very stiff section

which doesn't settle down into the bog.

It's a very ingenious solution.

- [Narrator] Through clever engineering,

Neolithic people had devised a successful solution

to traverse difficult terrain.

Though technically a trackway,

it displays some of the essential structural ideas

that would lead to bridges of the future.

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From the ancient world through to the modern day,

bridge engineers have needed to consider

several key elements

to make their structures viable.

- So bridges have to deal with the self weight,

the thing itself.

Live load which is the imposition of traffic

whether it be road, rail, pedestrians,

it changes, it varies.

It could be nothing. It could be very intense.

- It's gotta be able to withstand high winds,

maybe snow loads for example.

These are all very complex things.

So the engineers designing the bridges

have to factor that in to their calculations.

- [Narrator] The first people to fully understand

the forces at play on a bridge

were masters of mass scale engineering, the Romans.

- The Romans were incredible engineers.

They built astonishing things.

They built aqueducts. They built coliseums.

They built harbors. They built roads.

There is nothing they wouldn't try and build.

- [Narrator] They would take bridge building

to another level,

transform the map of Europe and make a mark on our planet

that would last to this day.

From 509 BC onwards, the Romans established a Republic

that would eventually stretch across Southern Europe,

Africa and some of Asia.

- The Roman Republic is predicated on constant expansion.

And if you've got any designs on power

certainly in the first century BC,

what you have to do as either a governor or a general

is to be seen, to be going to the far reaches of the empire.

- [Narrator] And one of the most essential pieces

of infrastructure to span the divide and conquer territory

were bridges.

- Bridges are really integral to the Roman project

because roads are when those roads encounter rivers,

they have to go over them.

But they're also symbolic

and they're demonstrating Rome's power

to reach beyond natural frontiers or natural barriers.

- [Narrator] One man who was determined to make a mark

on the Republic

was the most famous of all Roman generals.

- Around the time the Roman started looking to the North,

a new figure emerges who proved to be the greatest warlord

of the Roman Republic

and this is Gaius Julius Caesar.

He had enormous ambitions

and this included making himself famous

by being the first Roman to conquer Gaul.

- [Narrator] From 58 BC,

Caesar was engaged in a war with peoples

occupying a region of Western Europe.

But to cement his foothold,

he needed to stop its neighbors from Germania,

from their regular incursions.

- So you now have German tribes

crossing over the River Rhine,

are starting to interfere in Caesar's conquest of Gaul.

This is going against Caesar's plan and he doesn't like it.

- [Narrator] But lying between Caesar

and his desire to quell the Germanic rebellion,

lay a formidable obstacle that was 1000 foot wide in places,

the River Rhine.

To transport his army across it,

he needed to build a bridge and not just any bridge,

one strong enough to support his 10 Legion Army

of over 40,000 men.

- This is a challenge that is really going to cement Caesar

as someone who has the engineering prowess

as well as the military prowess to take on Germania.

- [Narrator] But the Rhine was potentially as challenging

an adversary as his enemies.

Undeterred in 55 BC,

Caesar launched his mammoth construction project.

Archeological evidence is scant,

but Caesar's own words in his campaign diaries

allow us to paint a vivid picture of its construction.

100 piles, each one and a half foot in diameter,

were driven at an oblique angle.

The piles were braced together in pairs

to create piers set 40 feet apart

at the top of which logs could be inserted

to create the foundation of the deck.

Heavy supporting posts were tied to the piers

at an acute angle

to act as buttresses on the downstream side

to help resist the forces of the river.

Further cross bracing may have been added

to strengthen the structure.

Planks were then laid to create the deck and roadway.

- And this technology enabled Caesar to build this bridge

which could span this enormous, fast flowing

continental river.

- [Narrator] Remarkable for a bridge of its size,

it was completed in just 10 days,

allowing Caesar and his army to cross into Germania.

But Caesar's next engineering move

was even more astonishing.

- He completely takes apart the bridge that he made

because you don't want to leave an open back door

to the Germanic tribes.

- He marches across, does what he wants to do,

marches back, pulls down the bridge

and it's all in a day's work really.

- [Narrator] Romans may have built other military bridges,

but for sheer engineering audacity,

nothing matches the Rhine Bridge.

- This is Caesar reminding people back in Rome

that he was still on the scene.

He could do really what he wanted with his troops.

Where Roman wants to go, it will go

is a message of this bridge.

- [Narrator] Caesar had perfected speed engineering.

And in the mid 20th century,

a man who tinkered with model bridges as a hobby

would turbocharge this concept

to help change the course of history.

(bomb explodes)

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At the outbreak of World War II in 1939,

Donald Bailey, a British civil servant,

devised an idea on the back of an envelope

for a military bridge.

So ingenious it is credited with contributing

to help end the conflict six years later.

- The Bailey bridges were an essential component

in keeping the Allies moving

and the German and Italian forces were systematically

blowing up bridges as they retreated,

And what the Allies needed was a solution.

- [Narrator] But bridge technology at the time

wasn't fit for purpose.

- The engineering elements of the armies

did have bridging solutions,

but they're often ready made quite heavy units

that had to be crane into place.

- The other issue they were confronted with

is that many of the bridges they were using

couldn't withstand the weight

of some of the heavier equipment, especially tanks.

- [Narrator] Enter the Bailey bridge,

a sectional pre-fabricated bridge that was easy to transport

and could be erected in a matter of hours

with only minimal assistance from heavy equipment.

Built from regular steel alloys and modular in form,

the bridge was assembled using a series

of crossed braced rectangular side panels

each up to 10 foot in length.

These could be carried by six men

and were connected using interlocking lugs.

19 foot wide transoms were then run between each side.

After one section was complete,

it was pushed forward over rollers

and another section built behind it.

They were then connected together with pins in the corners

of the panels.

To create the floor,

10 foot long stringers were added for support.

Wooden planking would then be placed to top the stringers

to provide a road bed.

- It's a very light way to create a rigid frame

and it's bolting together those sections of frame

that allow you to create quite long bridges

capable of withstanding the weight of a tank.

- [Narrator] But it was the quick modular assembly,

often without the need for support piers in the water,

which gave them the edge over the enemy.

- It's a bit like the flat pack furniture

you can buy these days.

It's modular. It's mass produced.

It goes together in a fairly easy way.

It could be put together pretty quickly,

moved and dismantled as needed.

- And so to have a kit of very few parts

which could quickly be replicated and shared with the Allies

meant that the Americans and the Canadians and the English

were all making components for the same bridge.

- [Narrator] A Bailey bridge could easily span

up to 230 feet

and if required, could reach over a thousand feet.

Once the troops had used the bridge,

they then took a leaf out of the Roman engineering playbook.

- In the same way that these bridges

could be put up very quickly,

just like the Romans with their Rhine Bridge,

they could be taken down very quickly and used elsewhere.

- [Narrator] By the end of the war,

over 3000 Bailey bridges covering more than 55 miles

had been constructed.

Leading British commander field Marshall Montgomery to say,

"Without the Bailey bridge,

"we should not have won the war."

- I think the real impact of the Bailey bridge

is that it allowed the Allied forces

to maintain that speed of advance.

That was absolutely critical.

And in that way,

these bridges played a really important role

in the defeat of Nazi Germany.

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(sheep bleating)

- [Narrator] By 27 BC, the Roman Republic

had transitioned into an empire.

As it expanded, they required more permanent infrastructure

that would last longer than wooden bridge technology.

- Wood can be washed away or get damp and rotted.

So that was a good temporary bridge building material.

To build a permanent bridge,

you want to build in masonry, in stone, brick and concrete.

- [Narrator] They turned to a design

which would change the face of construction

not just in the Roman era, but for all time,

the arch bridge.

- The Romans, they really were the sort of past masters

of taking their technological innovations of their day

and making them their own.

And in the case of the arch,

this is something they'd inherited from Greece,

but this was a key component in many of their structures.

If we look at aqueducts, stadiums, basilicas

and especially bridges.

- [Narrator] The ability of an arch to span a large area

is largely due to the force of compression.

- When things are pressed together,

obviously that is compression.

Tension is the precise opposite

where things are pulled apart.

And this is the things that engineers have to deal with

when they design and build bridges.

And they have to choose their materials carefully

because some materials are good in compression,

some materials are good in tension.

- [Narrator] Needing their bridges

to span further than ever before,

the Romans had upgraded to stone arches.

- Stone is a good material in compression.

And an arch is known as something which carries its load

predominantly in compression down to the foundation.

- [Narrator] To support arches over longer spans,

an innovative approach was required

to construct the piers mid river.

- The problem with that is you're building in flowing water.

You've got to find a way of keeping the water out

while you're working.

And one way of doing this is something called a cofferdam.

- [Narrator] The Romans developed a temporary barrier

so that the workers could build within a dry space

in the middle of a flowing river.

Vertical timber stakes were driven into the river bed

long enough so that a significant portion

was higher than the water level forming a walled dam.

The water in the cofferdam was emptied using either buckets

or an Archimedes screw.

Gaps between the stakes were sealed with clay,

providing a watertight area in which the foundations

and piers could be constructed.

Once the piers were built,

the cofferdams could be deconstructed and removed,

but the flow of water around the piers raised another issue.

- One of the biggest enemies of bridges

is actually the river scour.

That is where you've got a support in the water

and the river is constantly flowing around that support.

And if you don't shape the support properly,

the flow of water will actually erode around the foundation

and it's a very real risk.

- [Narrator] To help mitigate

this potentially catastrophic erosion,

the Romans devised a particular shape to the piers.

- You would tend to build each pier with a point at each end

called a cutwater or styling.

- It made the flow around the pier much more smooth.

So today likewise,

we shape our river piers carefully

so that the scour doesn't happen or it's minimized.

- [Narrator] Constructing the bridge's heavy arches

also required some innovative thinking

as they required considerable support

so that the growing span could be held in place

before being finally secured with a keystone.

A platform was built at the base of the pier

using a measurement called a springing line.

Temporary wooden support known as falsework

was erected in an arch shape from this line.

Separate wedge-shaped stones called voussoirs

were placed incrementally over the falsework frame

until a final trapezoidal keystone was inserted.

The sides of the keystone must be tapered

so that the force of the weight load

is channeled out and down.

Once the keystone had been set in place with concrete,

the falsework could then be removed

because compression and friction keep the structure stable.

- The keystone is the critical piece of the puzzle.

This allows the whole arch to work in compression.

And without that, you have no structural system

therefore you can't support any load.

- [Narrator] Buttresses were then added to stiffen the wall

against overturning forces.

Finally, the bridge was laid with a brick deck

and paved to carry soldiers and chariots.

- The Romans are rightly revered for their audacity

building on the scale that no one had seen before.

So the longest Roman bridge in their empire

was at Merida in Spain.

It's almost 2.5 thousand feet long.

- [Narrator] The arch bridge was such a success

that the Romans crossed almost every major river

in their empire

and many examples still stand to this day.

(dramatic music)

While the cofferdam allowed the Romans

to construct piers in rivers,

a development based on it that came almost 2000 years later,

allowed construction to take place not only in water,

but under it.

Completed in 1883, the Brooklyn Bridge

and it's almost 1600 foot long main span

linking New York's two most important boroughs,

Brooklyn and Manhattan,

broke the record for the longest suspension bridge

in the world.

But during its construction, catastrophe was never far away.

- The project suffered all manner of setbacks,

not least when the original engineer, John Roebling,

contracted and died from tetanus

as a consequence of an injury he suffered on site.

- [Narrator] The baton was passed to his son Washington,

who was now tasked to build the bridge's foundations

in the deep, fast flowing waters of the East River.

The solution was the caisson, which like the cofferdam,

was a technology also used by the Romans.

- To build really deep foundations for bridges

that are in deep water,

using a cofferdam is no longer really feasible.

So caissons were designed

that is essentially an upturned box

that can go down into the water

and displace the water from it with high pressurized air.

- [Narrator] Washington Roebling's pressurized caissons

were some of the first of their kind,

designed to ensure that the mud and water

below the water line

couldn't infiltrate the chamber

while the men dug out the area for the pier foundations.

- I can't imagine what it would've been like

to work in one of these caissons.

Damp, claustrophobic, struggling to breathe.

I mean it must have been like a hell on Earth.

- You're also in a pressurized environment

and the science of understanding what that pressure did

to the human body

and the change between surface level pressure

and caisson pressure wasn't properly understood.

- [Narrator] A local doctor noticed a worrying trend.

the deeper and longer the workers called sandhogs

stayed under water,

the more they suffered agonizing symptoms.

- Many of the diggers were suffering

from these sort of terrible pains and cramps in the bodies.

And they weren't entirely sure what it was.

They were bent double if you like

and that's the word that we now use to describe

a form of decompression sickness, the bends,

and this was a terrible problem for the engineers.

- [Narrator] At least 20 men died a horrible death

from Caissons disease

and it affected Roebling himself.

Eventually, confined to his home,

the chief engineer's job was passed to his wife, Emily.

- So for 10 years,

Emily was essentially acting as chief engineer.

And over that time,

she learned how to do calculations herself.

She understood the stresses and the loads

the bridge was under

so that she could ensure that the completion of this bridge

was done successfully.

- [Narrator] Over 10 years later at the opening,

Emily Roebling carried a rooster across the bridge

as a sign of victory

while her husband Washington could only watch

from his bedroom window.

- Emily Roebling was really a role model at the time.

Women weren't even getting education as engineers

let alone running these incredible projects.

So women engineers today have a lot to thank her for.

- [Narrator] Around 1485,

The great Italian Renaissance master Leonardo da Vinci,

had drawn plans for an extraordinary wooden bridge

which could support itself without bolts, ropes or nails.

But around 500 years earlier

in a very different part of the world,

ancient engineers had already devised a similar concept

that utilized their exceptional carpentry skills.

(light music)

Goods have been traded and transported from across China

for millennia.

Historical documents suggest that

the bridges traders needed to cross

suffered from structural problems

associated with their central pillars

being damaged by the force of flooded rivers.

Plank bridges, which removed the need for piers,

were even less reliable.

- A simple strat bridge of three planks.

It comes with all sorts of problems.

You can't span particularly wide distances

and the whole structure is also open up to twisting as well.

- There was too much movement in the bridge.

It becomes too flexible. It distorts under load.

So there was a need to do something different.

- [Narrator] The answer emerged 1000 years ago

during the Song Dynasty,

when it said a prison guard devised a new approach

which addressed these issues

through a unique construction method

that more resembled weaving, the woven timber arch bridge.

- So the way in which the timbers were placed together

in that interlocking form

gave the bridge a degree of flexibility.

Now all bridges need flexibility to stay up

but this was a sort of a really unique way

in which the forces could be dissipated

as the traffic passed over the top of the bridge.

- [Narrator] And they were built entirely

by using traditional woodworking techniques

and used no glue, screws or fasteners,

a method that was first practiced in Neolithic times.

- You could compare it to the skilled woodwork

in cabinet making for example,

where you've got mortise and tenon joints

that keep that structure together.

In these bridges, it's the same skilled woodwork

that makes the bridge so strong.

- [Narrator] Abutments usually made from stone

were built on rock to secure the bridge at each end

before construction began in three sections.

The first, a three-sided arch made up of three long beams

and two crossbeams.

The second, a five-sided arch of five long beams

and four crossbeams

was interlocked with the first.

And the result is a weaving effect

which gives the bridge its strength and stability.

Wooden planks were then laid over the substructure

to form a deck

and a roof was sometimes built over the top

for protection from the elements.

- It's so ingenious.

What the woven arch bridge does is it almost takes

two bridges that in themselves

are not quite structurally sound,

but by combining them, by interposing them,

actually you create an incredibly strong bridge

that can span wider distances.

- [Narrator] All Chinese bridges of this type

were thought to have disappeared

and the skills it took to construct them lost forever.

In the 1980s however, there was a shock discovery

when 100 were found in a remote mountainous corner

of Southeast China,

which inspired later designs.

- It's just such a wonderful moment to look on something

that you thought had gone

and to have that connection for past culture,

past civilization

and see in this case what engineers in the past

are really capable of.

- And what I find personally really fascinating

is that these bridges still continue to be constructed today

as part of an intangible cultural heritage

that's actually even recognized by UNESCO.

- [Narrator] They remain proof that the engineering skills

of these ancient master craftsmen

are still as pertinent today.

But the Chinese were not the only ancient engineers

to build bridges which would defy belief.

(light music)

The Inca rulers of their South American civilization

in the 15th century

used their skills to build perhaps the most vertigo inducing

bridges on the planet.

The Inca Empire stretched 3,400 miles from north to south

and extended along the Pacific Coast and Andean highlands

from the Southern border of Columbia to Central Chile.

It lasted from the 12th to the 16th century

where the Incas were overthrown by the Spaniards.

- But within that short timeframe,

their authority, administration,

the way that they organized groups of linguistically

quite varied people under one leadership

meant that they created really monumental things

and that's reflected in some of their structures.

- [Narrator] Key to this expansion

where bridges spanning up to 200 feet

but constructed incredibly using little more than grass.

- When we think of bridge building, we think of stone.

We think of wood.

Well imagine spanning vast caverns with grasses,

with plants,

and that's what these bridges do.

That's quite something.

- [Narrator] For their plant-based suspension bridges,

the Incas use their crafting skills

to twist lengths of grass, vines or leather

into short sections measuring up to a few feet in length.

These were then spliced with similar sections,

creating the length of multistrand rope required.

- So when you're twisting two ropes together

to make a rope of double the thickness,

it always wants to unlock.

But if you turn that rope on itself and then twist it again,

what you have is those two parts of the rope

working against each other.

They wanna unlock against each other but they can't.

- You can think about it like braiding hair

where you take two, three pieces

and you weave them together

and that increases the tensile strength

and this is what they were doing.

- [Narrator] Lengths of multistrand rope

could then be woven together

to create the thickest, strongest rope cables.

- So some of these ropes are huge.

They're the width of a human torso

and they're capable of taking really quite extreme weight.

- This is a huge undertaking.

There'll be whole communities,

whole villages coming together, weaving these cables.

- [Narrator] Each bridge contains up to 10 miles of rope,

each one weighing up to 200 pounds,

making a combined weight approaching a ton.

So how could these cumbersome materials

be hoisted up steep mountainsides?

- That would fall on some of the younger members

of the community, the most athletic.

They would have to get down, cross the river

with a stretch of this cord

and then climb all the way up the other side.

- It requires real bravery, audacity

to be over steep ravines with rocks,

but it became a way of life for the people

of the Incan Empire.

- [Narrator] The critical factor in this bridge's design

was how to secure the supporting ropes to the cliff itself.

The walkway was constructed of up to four braided ropes

while two smaller ropes were used for the handrails

with vertical suspenders joining them to the deck

spaced at around four inches apart.

These six ropes were then wound around boulders

which were wedged into slots in the cliff face

and acted much like bollards

to securely tether the bridge to the mountain side.

- It's absolutely critical

that these things were tethered correctly

because if they weren't,

you run the risk of losing the work of a whole community

and potentially lives with it.

- [Narrator] A 100-foot bridge could easily take

7,500 pounds or 56 people,

three or four times the load that was required,

a similar ratio used to build bridges today.

- You may get entire communities, armies

moving across these bridges because the rope is so strong.

- [Narrator] It's estimated that a large rope bridge

would take around two weeks to construct

and could last as long as two years

dependent on conditions

but regular maintenance could extend their life.

- In that moist jungle environment,

they absorb the humidity.

They stretch through the forces put on them.

You can have friction wearing away

at the ends where they're tethered.

You can have rot as well.

- [Narrator] These entirely organic bridges

were strong enough that they could take an army on horseback

marching two by two,

which provided the perfect platform

for the oncoming invaders.

- The problem for the Incas

is of course that the same bridges that had opened up

vast ways of landscape to their kingdom

were the same bridges that were used by the Spanish

during the conquest.

- [Narrator] In 1492,

the Spanish Army known as the Conquistadors,

arrived in the Americas.

And by 1531, had reached the Inca Empire,

making full use of the Inca engineering.

- These bridges had facilitated free access

and free movement

throughout the Inca's landscape.

But of course because of that,

it was also part of their downfall

because these were the routes that were used

by the Spanish conquest of the area.

And this was probably not the original function

that the Incas had in mind.

- [Narrator] By 1572, Inca rule had completely ended

but it hadn't all been plain sailing for the Spanish.

They had to suspend their disbelief

when they first saw the swaying bridges.

- I would feel the same way

if I'd stumbled across one in the middle of nowhere.

I'd take some convincing to walk across it.

(dramatic music)

- [Narrator] Stability under all conditions

is something modern bridge builders

have also had to take into account.

But even today, engineers learn as much from failure

as they do from success.

The image of the Tacoma Narrows Bridge in America,

buckling violently in 40 mile an hour winds in 1940

remains a disturbing reminder

that sometimes things can go very wrong

even with the best engineered projects.

- The Tacoma incident was one of those moments in history

where it stopped us dead in our tracks

while we tried to work out what an earth happened there.

- One of the difficult things to realize

is that bridges are mobile structures

because they're constantly being moved,

buffeted by wind.

Then unless you build in a certain mobility,

a flexibility into their design, it will be a disaster.

- [Narrator] Despite being designed and built by engineers

with a strong track record in bridge construction,

a then little understood natural phenomenon

set off vibrations caused by whirling masses of air

known as vortices.

- So wind blowing on the bridge, creating vortices,

which creates a fluctuating change in pressure.

And if it coincides with the natural frequency

of the bridge,

then the bridge response starts to amplify

and get bigger and bigger and bigger

until you get to that horrible collapse point.

- [Narrator] The solution to eliminate the possibility

of such vibrations escalating

comes through engineers installing

specifically designed devices called dampers,

which counter the effect

of this potentially catastrophic movement.

- There are different types of dampers

but essentially what they're doing is dissipating the energy

of the vibration of the structure.

If you think about the shock absorbers on your car

or a mountain bike,

it's reducing the magnitude of that movement or that shock

that you would feel.

- [Narrator] One type is called a tuned mass damper.

- We have this weight supported on sprung system

so that it has a frequency

which is tuned to the same frequency as the bridge.

- [Narrator] As the bridge moves,

the weight moves in the opposite direction or out of phase,

which counteracts the forces,

helping to reduce any movement in the structure.

As well as canceling out the vibrations

caused by wind vortices,

dampers can also reduce damage and metal fatigue

caused by other phenomena including earthquakes.

And as with all technologies,

new understandings continue to be made.

- Recently, there's been more work done

in trying to understand the complex nature

of the interactions of air with structures like bridges.

This helps us to ensure that any future design

will be strong and resilient

to even the most extreme loading.

- [Narrator] But these breakthroughs were only made possible

by the enormous technical advances

made almost two centuries earlier.

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It can be argued that bridge building came of age

with the birth of the Industrial Revolution.

- Casting with iron had been around

for really quite some time

but it was time consuming and done mostly by hand.

What we see in the middle of the 19th century though,

because of innovations in both chemistry and furnacing,

is that whole process can be scaled up

to produce both more and objects of a much bigger size.

It was this upscaling in material outputs

that fueled arguably the greatest increase in production

the world had ever seen.

- [Narrator] From 1760 to around 1840,

these advances propelled industrial economies

through the designing and constructing

of massive infrastructure.

In England during this time,

one man stood head and shoulders above all others

when it came to engineering prowess.

- Isambard Kingdom Brunel

is probably one of the most renowned engineers of all time,

whether it was ships, whether it was railways, bridges.

You know this is one of the key figures

of the Industrial Revolution.

- If you literally thumb through his notebooks,

you can see that this is a genius man.

- [Narrator] In 1831 at age 24

and while still an engineering novice,

he won a competition to build a bridge over the River Avon

in Bristol,

which would make travel in both directions much easier.

To span the formidable 245 feet high 700 foot wide gorge,

Brunel came up with a radical idea in Britain at the time

to put Bristol on the map, a suspension bridge.

- In a suspension bridge,

you've got the perfect balance of tension and compression.

So you've got the tension in the cable

and the suspenders that actually connect the catenary cable

to the deck itself.

But as the cable goes over the towers

and is anchored into the ground either side,

those cables are actually transmitting compressive loads

through the towers.

- [Narrator] On the Clifton Suspension Bridge,

six rod iron chains, three on either side, span the bridge

and hang over two 86-foot tall towers.

Metal saddles sitting atop the towers are in compression

as they take the weight of the chains as well as the deck,

which is attached to them via 162 vertically hung

iron suspender rods.

Construction began in 1831 and Burnel's first hurdle

was to choose the most suitable rock

for the foundations to carry the bridge's enormous weight.

- However, the problem with the Avon Gorge

is that the rocks were unstable on either side.

So the solution that Brunel came up with

was to build two enormous abutment chambers

which he then used to support the pylons above.

- [Narrator] Already beset by a shortfall

in construction funds,

tragedy struck in 1859 when Brunel passed away

having never seen his bridge completed.

It wasn't until 1862 with new engineers in charge

that work finally resumed

but Burnel's replacements faced a considerable challenge.

- Whenever you build a suspension bridge,

you need to build some means of getting the cable

or in this case the chains across the gap

cuz until you've got those up,

you can't bring up the bridge deck to hang off it.

- They had to build a platform across the gorge

in order to carry the weights of these chains

which were enormous.

- [Narrator] This came in the form

of a temporary wooden platform secured to lighter cables

which was curved to match the hang of the chains.

A movable carrier traveled along the cable

to secure each of the 4,200 links into position.

- So once these chains have been coupled up,

they're going to support the bridge structurally.

What you need to do is tether them

to either side of the gorge.

- [Narrator] The chains were anchored through hollow shafts

tunneled into the bedrock.

A land saddle angles them into the tunnel

while a brick anchor plate

attached to the ends of the chains

prevents them from being pulled out.

- So it doesn't matter how much you pulled on the chain,

it would bang itself against the bedrock.

- [Narrator] With the chains tethered,

the temporary platform could be removed

and vertically hung iron suspender rods

could be connected to them to support the deck below.

Once roof caps were put on to cover the chain saddles,

the Clifton Suspension Bridge was finally opened

33 years after Brunel had begun it.

- The completion of the bridge

largely to Brunel's original designs

was seen as a memorial to the great engineer.

It is one of the great iconic symbols

of the Industrial Revolution.

- [Narrator] It remains to this day

an amazing achievement of both Victorian engineering

and Brunel's incredible vision.

(dramatic music)

The development of new materials paved the way

for much larger and stronger bridges

to meet the new demands of the 20th century.

- It's amazing to think

that in the course of around a 100 years,

we'd gone from roads that were in essence

on a single horse track

to having 12 lanes super highways.

At some point, this traffic needs to come together

to cross an expansive water or a river.

So these bridges need to be future proof

to take these excessive loads.

- [Narrator] Opened in 1932,

Australia's iconic Sydney Harbor Bridge

took the arch to a whole new level,

replacing rot and cast iron with a much improved

and stronger material, steel.

Spanning 1,650 feet,

it is one of the longest steel arch bridges in the world.

And at 440 feet high, the tallest.

It is held together by six million hand driven rivets

and carries loads of more than one million cars,

trucks and trains every week.

- This really is an absolutely monumental bridges.

It's a tremendous sight and you can only really

imagine the challenges that engineers would face

by trying to get across this enormous span of water.

- You're building this huge arch

from opposite sides of the harbor

and they've got to meet in the middle.

Without our modern day computer systems,

you think how on Earth did they do that?

- [Narrator] The deep water of Sydney Harbor

made building pier supports impractical.

Somehow during the construction,

the mammoth steel arch spans needed to be supported

as they were being assembled toward each other

from opposing banks.

- What they did was they attached very high strength,

steel cables to the construction as they were working

so this to stop the thing falling over

and these cables were anchored in the ground.

So they would then be able to incrementally grow the arches

a little bit by little bit.

- [Narrator] Huge steel pivots at the base of each arch

allowed the cables to be tightened or slackened as necessary

to remain on course.

- Right from the very beginning,

every time they put a piece on,

they would've had to do a survey,

making sure that they were following the line

that the arch has to follow

so that it was going to meet in the right place

in the middle.

- [Narrator] After seven years of construction,

the gap was closing.

- So as those two arches come close to each other,

you could begin to see whether one's high or low

or whether if one was slightly twisted.

- [Narrator] The engineer's foresight

proved vital to this critical moment.

- There was a need to pull out on one side

and pull in on the other side and make a bit of adjustment.

In fact, it was quite surprising

that the amount of adjustment was as small as it was.

- This was a period when they didn't have

sort of laser sighted surveying equipment.

They were working with pen and paper and slide rule.

And when you take all of that into account,

the fact that they were just over an inch out

is really quite remarkable.

- [Narrator] This relatively minuscule adjustment

saw the two arches finally meet up as designed.

- There's a very special occasion when two parts of a bridge

meet for the first time.

And of course at Sydney, would've been terribly significant,

that meeting of the arch and the great celebration.

- [Narrator] The Sydney Harbor Bridge

owes its existence to the 1400 laborers and many engineers

that brought two sides of Sydney together

by manipulating solid steel to maximum effect.

(dramatic music)

Modern bridges have not only united both sides of a city,

but even countries themselves.

The mile long Bosphorus Bridge in Istanbul

links the continents of Europe and Asia.

While at five miles long,

the Orison Bridge is the longest combined road

and rail bridge in Europe

joining Sweden to Denmark.

Orison may look like a suspension bridge

but it's appearance is deceptive.

It uses cable state technology,

a design feature of some of the longest bridges

in the world.

The most remarkable of these is in France,

the Millau Viaduct.

- I gotta say Millau is probably one of my

favorite pieces of engineering.

I mean it's elegant.

It's sleek. It's slender.

It's French.

- [Narrator] At over 1000 feet, the Millau Viaduct

is the tallest bridge in the world,

standing higher than the Eiffel Tower.

Completed in 2004,

its design utilizes the cable stay principle.

- So you've got a mast and the cables run from the mast

well like a coat hanger and support the bridge deck.

And normally, a conventional cable stay bridge

would have two towers and one main span in between.

In the case of Millau Viaduct, it's a little different

because there are seven of these towers.

- [Narrator] Building a bridge

one and a half miles in length

with a deck almost 900 feet above ground

was never going to be straightforward.

And like with all enormous structures,

fluctuations in temperature had to be taken into account.

- As you build a big bridge, the thing moves around.

In the morning, it will be, it'll be cold.

And as the sun comes out and it gets warm, it moves.

It grows. It expands.

So as bridge engineers, we get used to this

this amount of movement

and it's quite a lot quite surprising,

alarming to somebody who's not used to it.

- [Narrator] This movement,

especially of the deck which sits on the piers,

can cause destabilization.

But the Millau engineers had a unique solution

that had never been tried before.

- These very tall concrete piers are split.

The top part is in two well like a tuning fork.

As the bridge changes in temperature,

the bridge will expand and contract.

And that means the tops of the piers would move with it.

And if they were very stiff,

those peers would then generate very large forces.

But in fact by splitting it, making them very flexible,

those forces are not generated.

And so it's a very clever way of dealing with

what we call the articulation of the bridge.

- [Narrator] Millau's projected 124 year lifespan

is due to such innovative design.

In many ways, making it the shape of bridges to come.

(light music)

From their earliest days,

when humans overcame the challenges of crossing rivers

to trade and link communities,

we have continued to invent ever more extraordinary ways

to build bridges

from the death defying to the sublime to the iconic.

Bridges continue to serve a vital function in societies:

that of uniting people, enabling travel and commerce

and acting as conduits to our future prosperity.

But none would've achieved these lofty ambitions

without the skill, daring and ingenuity

demonstrated through innovations by ancient engineers.

(dramatic music)