Original subtitles

Narrator: The golden gate bridge,

The washington monument,

The empire state building --

These and four other engineering marvels

Are regarded by many as the wonders of america.

Seven iconic modern-day mega-structures

Set the benchmark for american ingenuity.

How were they built?

And what secrets do they conceal?

Today, investigators use hidden records...

It's a monumental project 'cause it hadn't been done before.

Narrator: ...And dynamite...

That's how you break it up good.

Narrator: ...To decode the mysteries

Of america's world-famous icons.

Across the united states,

These massive monuments define a nation's identity.

How do engineers overcome the incredible challenges

Of building bigger than ever before in untamed landscapes

And in the heart of great cities?

We reveal how the most powerful nation on earth

Enters a new age of engineering achievement

To build the seven modern wonders of america.

♪

The seven wonders of the ancient world

Span three continents

And thousands of years of history.

But today, a new generation of engineering wonders

Rises to take their place.

How does the united states alone

Match the engineering might of the entire ancient world

Across a new and untamed continent?

The national mall in washington, d.C.,

Is america's most visited national park.

It's also the home of some of the country's

Greatest monuments.

At one end, the lincoln memorial

Honors one of the great american presidents,

A gigantic seated statue

Inspired by an original ancient wonder in greece,

The great statue of zeus at olympia.

At the other end, congress meets in the united states capitol.

And on the northern side,

The world-famous home of the u.S. President,

The white house.

All of these monuments copy the grand architecture

Of the classical world...

...With their elegant columns and pediments.

The most extraordinary stands proudly

In the center of the mall,

The first modern wonder of america --

The washington monument.

In 1836, america's capital is growing fast.

The people of the city want to build a memorial

To their founding father

And first president, george washington.

The ambitious plan is to ship in stones

From all over the united states...

And assemble them into an audaciously thin stone tower.

This tower will be the tallest structure ever built.

But the design is nothing like the classical architecture

Found elsewhere on the national mall.

What inspires the strange shape of this modern wonder?

In the early 19th century,

Investigators discover the remains

Of two gigantic ancient obelisks in alexandria, egypt.

They excavate one which has fallen

And is buried under centuries of sand and debris.

Each stands nearly 70 feet tall and weighs almost 200 tons.

They're carved from red granite

And are decorated with ancient hieroglyphs on all four sides.

These incredible obelisks inspire the shape

Of the washington monument.

But why do the people of d.C. Choose an egyptian-style design?

A clue lies in egypt.

The temple of karnak near luxor

Once boasts at least 13 obelisks...

Including some of the most impressive ever raised.

The tallest is over 118 feet high.

Today, in the center of the temple, only two remain.

But the obelisks don't disappear.

They're looted.

In ancient times, the romans ransack egyptian temples

And ship obelisks all over the world...

To constantinople, now istanbul...

And to rome.

At 105 feet tall,

It's the largest ancient obelisk in the world.

The romans fill their city with eight large

And 42 small egyptian obelisks.

The desire for these ancient monoliths

Continues into the 19th century,

Only 15 years before the people of washington

Design their monument.

Other great modern cities

Start to raise their own egyptian obelisks.

One is shipped to paris

And re-erected in the place de la concorde.

A second is placed in london beside the thames.

And the last is raised in new york's central park.

Here they still stand...

Symbols of great power

Connecting these modern metropolises

With the majesty of the ancient world.

The people of washington want to join this exclusive club

By building their own obelisk.

But they go one step further.

This obelisk will outdo them all.

In 1848, this will be the tallest structure ever built.

In six years, the monument rises more than 160 feet

Above its foundations.

But in 1861, the country plunges into civil war.

Work grinds to a halt.

The project kick-starts 20 years later,

When lieutenant colonel thomas lincoln casey takes over.

When he arrives to inspect the site, he's in for a shock.

The tower isn't even a third of its planned height.

It sinks more than three feet into the ground

And leans to one side.

Casey unearths the foundations of the tower

And remove soil on one side to straighten the monument.

Then he digs a series of tunnels

Down to a firm layer of clay

And fills them with concrete.

From these new foundations,

He then constructs buttresses up to the base of the tower.

Then he can start building up.

And 36 years after work began,

The washington monument finally reaches its full height.

Thanks to casey's work,

The washington monument is a solid success.

By 1888, around 55,000 people scale it every month

To proudly stand on the tallest structure in the world.

The washington monument climbs far above the ancient obelisks

That inspire its design

And sets a precedent for the new world wonders that follow.

But before the final stones

Are placed on the washington monument,

Another iconic structure is already rising in new york.

At the entrance to the city stands a mighty guardian,

The second modern wonder of america --

The statue of liberty,

One of the most famous monuments in the world.

Built as a gift from France to america

To mark 100 years of independence,

She has become an icon woven

Into the fabric of the united states.

How do engineers create a statue in the modern era

Worthy of the great wonders of the world?

There are all kinds of unknowns.

There are secrets about the statue of liberty.

There are mysteries,

And it's really a lot of fun to try to uncover them.

Narrator: Looking out over new york from a staggering 265 feet,

The statue is an enduring symbol of freedom.

Made from 62,000 pounds of the purest copper,

Supported by an ingenious metal skeleton...

...She stands on top of a mysterious 11-pointed star...

And tramples on the chains of oppression

With her enormous feet.

Holding her torch high into the new york skyline,

She is one of the world's most recognizable landmarks.

The statue of liberty is a modern engineering wonder.

But what is the inspiration for this magnificent monument?

Have the seven wonders of the ancient world

Influenced its design?

Historian and author ed berenson

Spends years trying to uncover the inspiration

For new york's most famous resident.

When we try to figure out

What the inspiration for the statue of liberty was,

We have to make our own interpretations

Because bartholdi didn't write down very much.

Narrator: Completed in 1886,

The statue of liberty is french sculptor

Frédéric bartholdi's masterpiece.

At first glance, it looks like the statue

Is modeled on libertas, the roman goddess of freedom.

Berenson: Right from the beginning, the real name

Of the statue of liberty is liberty enlightening the world.

Narrator: The same goddess of freedom

Also appears on the great seal of France,

But is there more going on here?

Ed thinks bartholdi is actually looking

Even further back in time

To one of the ancient wonders of the world

Which experts believe features a very similar-looking headpiece.

Berenson: This is the colossus of rhodes, and this was an image

From the middle of the 19th century.

This is what people then thought the colossus of rhodes

Must've looked like.

Narrator: The 110-feet-tall statue

Is one of the seven ancient wonders of the world.

It represents helios, the greek god of the sun.

It stands on the greek island of rhodes 2,300 years ago,

But it's destroyed just 66 years after it is built.

It was a great statue, a huge statue,

Carrying a torch,

With a crown that had spokes on it,

And those spokes represent the rays of the sun.

Narrator: So is this really where bartholdi

Gets his inspiration from?

Berenson: We know that he was interested in colossal statues.

He was amazed by them and he said that he wanted

To build something just like that.

What bartholdi did is he amalgamated the two.

He took the goddess of liberty

And he fused it with the colossus of rhodes,

And out of that came the statue of liberty.

Narrator: The welcoming face of the statue of liberty

Greets new arrivals into new york

For more than 150 years.

But when she first rises above the hudson river,

She looks very different --

Much more like a statue from the ancient world.

62,000 pounds of the purest copper

Make up the statue's skin,

Hammered into over 300 plates.

Each plate is less than one inch thick.

A thick layer of green patina covers every part of the statue.

But stripping away 130 years of oxidation

Reveals the lady's true color.

When first built,

She looks like a gleaming golden colossus of ancient times,

Towering over 19th-century new york.

The statue of liberty stands tall

As a modern wonder of america, watching over new york city.

But the ancient colossus of rhodes

Collapses after just 66 years.

How do engineers ensure

That lady liberty doesn't suffer the same fate

And stands strong in the face of ferocious atlantic winds?

And to build another ancient wonder,

A team of engineers in south dakota

Face an even greater challenge --

To change the face of an entire mountain.

Narrator: For more than a century, the statue of liberty

Stands proudly on its plinth, watching over new york harbor.

The famous colossus of rhodes, on which it is modeled,

Is shorter and built of sturdier stuff,

Yet it collapses after just 66 years.

How do liberty's engineers ensure

She outlives her ancient greek ancestor?

Veteran structural engineer donald friedman

Is one of america's leading specialists

In renovating historical buildings.

He investigates how the statue of liberty

Has stood the test of time.

Friedman: She's an amazing statue.

When you look at her from the outside, you know,

You see what everybody has always come here to see,

But when you go inside, you see the structure,

And it's even more interesting.

Narrator: Underneath her robe

Lies a vast, hidden lattice of intricate metalwork.

A huge central pylon anchors her to the pedestal...

...And acts as a spine for layers of steel girders...

...Supporting a framework of thin metal bars...

...That attach to her copper skin.

♪

So how does this seemingly fragile frame

Make lady liberty stronger than the great colossus of rhodes?

To solve this mystery, don first needs to understand

Exactly how the colossus collapses.

Nice to see you.

Don works with veteran physicist neville reiger,

Who has been researching the fate

Of the massive ancient statue for over 20 years.

This is what we think that the colossus looked like.

It stood pretty much with its legs close together.

Certainly not straddled over the harbor.

In 226 b.C.,

The island of rhodes is struck by an earthquake.

Neville has built a computer simulation

To investigate why the colossus falls.

It would have failed at the ankles.

That would've brought the entire structure down.

And that's what they saw lying on the ground

For 700 years.

Don believes the statue of liberty's designer

Takes this into account.

If you look at a person, we're big in the middle

And then we get narrow down towards the ankles,

And that's the weakest part of a statue.

Narrator: The narrow legs and ankles of the colossus

Make it susceptible to collapse.

So bartholdi designs liberty

To have a wide, flowing robe at the base.

The robe makes her more structurally sound.

The sturdy base will also

Help her deal with a more likely threat...

Strong winds.

Friedman: The sculpture itself is a very thin copper skin,

And even with a good shape

And even with the good geometry that the dress gives it,

There's still the issue of how do you make this strong enough

To withstand the wind pressure that's blowing on it

On a day like today, for example?

Narrator: So why hasn't the wind ripped off liberty's thin copper skin?

Friedman: In order to provide the structure

For this massive sculpture, the artist employed one

Of the most famous engineers of the era

And arguably the best engineer in France, at that time.

Narrator: Bartholdi recruits

A rising star of the construction industry,

An engineer who later builds a tower in paris, France,

That takes his name --

Gustave eiffel.

Inside that thin copper skin,

You've got a wrought-iron braced frame

That is the main structure of the statue,

Designed by the engineer gustave eiffel,

And it's very similar to the tower

That he built in paris a few years later.

Narrator: A solid central pylon made from four columns

Reinforced with crossed diagonal girders

Gives the statue super strength.

The central pylon supports a second steel frame,

Which attaches to the statue's skin

With flexible rods and strips of metal.

These strips are held in place with copper saddles

So that the two layers move independently.

The connections between the skin and the skeleton

Act as a spring, allowing the statue to sway and flex.

Engineers use cutting-edge techniques

To push the boundaries of what's possible

To build this modern wonder.

Lady liberty may resemble the statues of the ancient world

But stands taller and prouder

Than anything that has come before,

An icon of american identity in the middle of new york.

But why is one of the most important

Modern wonders of america

Here on an island in the hudson river?

Hidden secrets under the base of the statue might reveal a clue.

And how do engineers in south dakota

Carve a monumental sculpture worthy of the ancient world

In the middle of the american wilderness?

♪

Narrator: The statue of liberty, a modern wonder of america

Familiar to billions across the world.

Nearly 150 years ago,

Her designer, a french artist, frédéric bartholdi,

Knows what he wants his statue to look like...

But his biggest problem is finding a place to put her.

Archaeologist joel dukes

Is on a mission to uncover why lady liberty

Stands on an island in new york harbor.

Dukes: Could've been at the mouth of the harbor,

Which is several miles up this way.

It could've been on manhattan, at the tip,

Or even in central park.

Ultimately, though, they decided on liberty island.

Narrator: So why is one of the modern wonders of america built here?

Hiding in plain sight beneath the statue's feet

Is a military fort.

The fort is shaped like an 11-pointed star...

And is much older than the statue.

Thousands of precisely carved granite blocks

Make up its walls,

And inside sits the statue's foundations --

A massive slab of solid concrete,

20 feet deep and weighing 27,000 tons.

Why is the statue built on top of a fort?

Can the unusual shape provide a clue?

Dukes: Fort wood is a star fort, has 11 points on it,

And the interesting thing is that it's unique

Among the forts in new york harbor.

Narrator: In fact, fort wood is the only fort of its kind

In the entire united states.

And it's still giving up its secrets.

Joel thinks he's found another clue to the fort's violent past.

The team uncover a curved wall

That runs alongside the existing star-shaped one.

Dukes: Here's the island.

Here's the fort with the 11 points

And the outer wall curved around each of the points like this.

What we suspect is that the wall went

Around the fort at one point.

Narrator: The more he examines it, the more joel believes

It might be something else altogether.

So what it looks like is this isn't actually a wall.

What this is is a foot or two, a support for a moat.

Narrator: A moat here reveals soldiers need 360-degree defenses.

They aren't just worried about attacking ships,

But attacks from the land, too.

Protecting from a land invasion

Would've been part of the defenses at this fort.

Narrator: The fort's unique, 11-pointed shape

Gave defenders a huge advantage.

It dramatically increases their field of fire

And reduces blind spots.

Cannons positioned on one side of the fort

Can fire across to the other...

[ cannons firing ]

...Hitting anyone attempting to scale its walls.

The fort's low profile allows for thick granite ramparts

Protecting it from cannon fire.

But the development

Of more powerful artillery and explosive shells

Means the fort soon becomes outdated.

And it gradually falls into disrepair.

Dukes: Once the fort became obsolete,

They began to repurpose it for different things,

Such as a barracks, and a quartermaster's

And even a lighthouse keeper's quarter was put out there.

Narrator: Joel believes that,

Because the fort is no longer of military importance,

It can be repurposed easily and cheaply,

This time as the ideal base for a huge statue.

Dukes: I think that it was really fortunate to find fort wood.

I think the star design fits really well with the pedestal

And the statue out there on liberty island.

Narrator: Thanks to the position of this fort,

The statue of liberty has stood for more than 150 years

To greet any visitors arriving into new york.

For many, this is their first glimpse of america,

An enduring image of the promise of an entire nation.

The statue of liberty and the washington monument

Emulate and surpass the ancient wonders that inspire them.

But a team of engineers in south dakota

Take the challenge of conquering the american landscape

To a whole new level

By constructing the most ambitious wonder of america yet,

Mount rushmore.

And how do engineers on the west coast

Overcome the constant threat of killer earthquakes

To construct the longest bridge ever attempted in the world --

A unique american wonder, the golden gate bridge?

Narrator: The seven modern wonders of america

Look to the ancient world for inspiration.

Early civilizations fill their world

With gigantic stone sculptures

That honor their gods and rulers,

Like the great pharaoh ramesses at abu simbel in egypt

Or the statue of zeus at olympia in greece,

One of the original wonders of the world.

The third modern wonder of america

Takes this idea to the next level

As the most ambitious of them all -- mount rushmore.

The idea -- to honor four

Of the greatest u.S. Presidents in history.

It's a monumental project 'cause it hadn't been done before.

Narrator: Carved directly into south dakota's black hills,

Four gigantic faces tower 60 feet tall.

Hollowed-out irises plunge 2 feet into the cliff,

Leaving a thin pillar to appear like a sparkle in their eyes.

Epic 20-foot noses, each taller than three people.

Intricate twisting spectacles 12 inches thick.

And finely crafted facial hair.

These incredible sculptures take 14 years to make.

How do engineers construct

Such an epic modern wonder of america?

It's the brainchild of danish-american sculptor

Gutzon borglum.

Historian laura pankratz investigates how borglum carves

His giant masterpiece from a solid mountain.

She wants to know how he deals

With the epic engineering challenge

He faces at mount rushmore.

Pankratz: Gutzon was a very ambitious person.

He would say things like,

"there was great civilizations in rome,

Incredible monuments in egypt.

I want this monument to be around for thousands of years."

Narrator: Mount rushmore's creator attempts a feat

Of precision engineering not seen on this scale

In the united states before.

It was very different to be able to remove

A small piece of stone in the studio

In comparison to removing 450,000 tons of rock

Off of a mountain,

And one mistake, and there's no putting it back.

Narrator: Gutzon borglum's has to find over 400 workers

With experience of rock-hard granite

To even begin construction.

The depression was going on, so there wasn't a lot of work.

There was a lot of unemployed miners here,

And they were happy to go to work for borglum.

Narrator: Mines are dotted right across south dakota.

Miners here have years of experience

Removing thousands of tons of hard rock

In search of valuable minerals,

Such as mica, natural stone, and gold.

Borglum harnesses their pioneering mining technology

To start transforming a remote mountain of granite

Into a magnificent monument.

In 1927, they begin carving,

But instead of using chisels,

Workers use dynamite.

They blast away the mountain,

Leaving the outline of four giant heads.

Next, they drill 3-inch holes all over the rock's surface

To carve the features of the famous faces into the rock.

And for the finishing touches,

They use air-powered hammers to smooth the sculpture.

But how can you carve a mountain with dynamite

While dangling over 50 stories high?

♪

Wayne van hout runs the milbank granite quarry in south dakota.

He's an explosives expert and granite cutter.

Van hout: Granite is extremely hard to work with.

A shortcut in that is we can use explosives,

But when you use explosives, if not done right,

It can cause damage to the stone.

Narrator: Wayne wants to understand how dynamite

Can help carve the figures at mount rushmore.

He experiments with their techniques

And starts by testing explosives on a reject granite block.

We'll put one stick of dynashear in each hole.

The holes here are drilled random.

♪

Oh, that's how you break it up good.

Of course, you don't end up with much left when you're done.

Out here, we can do a blast pretty much any time of the day.

At mount rushmore, they used to do it twice a day.

The reason for that was they had to clear the mountain

When they did do their blasting.

Everybody'd have to climb up the ropes

And get off the mountain.

It must have been quite an ordeal to get it done.

Narrator: In the hands of experts,

Dynamite can remove rock

To a remarkable accuracy of within 3 inches.

At mount rushmore,

This leaves behind a rough outline of the face.

But how do you sculpt the crucial final few inches?

On mount rushmore, they would have come in with jackhammers

And start grinding that away to make it smooth.

The polished face, they call it.

Narrator: The workers remove the final 3 inches

With a technique called honeycombing.

They use jackhammers to drill a tight pattern of holes.

This weakens the granite and allows small pieces

To be accurately removed with hand tools.

They pound the rock to a smooth finish

By loosening the drill bit in their air hammers,

A method known as bumping.

I got a small 12x12 area done.

Went really fast for me,

But I'm not hanging from a rope off the side of a mountain

Trying to go straight in with this,

Trying to make it all the perfect shape.

But when you're all done,

This is what they called their polished surface.

It looks great.

Narrator: Achieving this level of detail at the giant scale

Of mount rushmore takes 14 years.

Borglum has to start from scratch.

When he arrives in the black hills wilderness,

There isn't even a road here.

To realize his epic vision,

He first needs giant infrastructure.

A small city springs up at the bottom of the mountain,

Complete with new roads, blacksmith shops,

And tool sheds.

A steep, 760-step staircase

And a cable car take the workers

To the top of the mountain over 5,000 feet high.

Winches lower the carvers down onto the faces,

Dangling hundreds of feet above the ground.

Giant compressors pump air up the mountain

To power the pneumatic drills and custom-made air hammers.

Adapting american mining techniques allows workers

To overcome the wild mountain range in south dakota

To forever stamp the images of the great american leaders

On the landscape

And surpass the achievements of the ancient world.

But is there more to this modern american wonder

Than a tribute to past presidents,

A hidden purpose to secure the national identity?

Clues are concealed inside the mountain.

And as the usa emerges as a modern global superpower,

A brand-new record-breaking engineering wonder appears...

...An icon of the 20th century

Unlike anything the world has ever seen before.

Narrator: Across the united states,

The incredible seven modern wonders of america

Test the boundaries of engineering.

Mount rushmore is hewn directly

Into the mountains of south dakota

To honor the great american presidents.

But is there more to this monument than meets the eye?

The seven wonders of the ancient world are riddled with secrets.

The largest of them all, the great pyramid of giza,

Contains hidden passageways and concealed rooms.

And mount rushmore is no different.

Behind abraham lincoln's head lies a secret tunnel

Extending 70 feet deep into the rock,

But it hits a dead end.

A 1,200-pound granite capstone

Seals an underground chamber at the tunnel's mouth.

Inside, a titanium vault

That contains a long teak casket.

And carefully stacked inside,

16 super-thin enamel panels.

Why are these mysterious tablets hidden inside mount rushmore,

And why is there a tunnel that seems to lead nowhere?

In washington's library of congress,

Architectural historian paula reed

Hunts for an explanation.

There are thousands of documents

Detailing mount rushmore's evolution

Among the personal papers of its creator, gutzon borglum.

Reed: There's a lot of correspondence,

Dealing with congress to get funding.

A lot of the funds were matched with private funds,

So there was also going out

And beating the bushes for private donors,

So funding was a problem from the beginning.

Narrator: The monument is initially budgeted at $250,000,

But costs quickly soar to nearly $1 million.

Reed: They kept running out of money.

And there would be an appropriation,

And it would get spent, and then work would stop,

And then there would be another appropriation.

Bair: And here we have records that were kept in 1939 and 1940.

Narrator: Paula wants to understand

Why the project keeps running out of money,

So she works with the collection's historian,

Barbara bair.

Gutzon borglum did change his mind a good bit,

And things evolved.

Narrator: Gutzon borglum's vision of mount rushmore

Expands over time.

They're searching for evidence

Of his most audacious and expensive plan.

So, these are oversize items.

Original blueprints reveal detailed designs

For a complex around the finished monument.

Reed: Part of the proposal of gutzon borglum

Was to have this grand staircase that would allow visitors

To climb all the way up behind the heads.

Narrator: The staircase leads

To the majestically titled hall of records.

Borglum describes a chamber hidden within the mountain

That explains mount rushmore's purpose

And houses a depository of the country's most sacred texts.

It would have copies of important documents

Like the declaration of independence,

The constitution, and an explanation

Of who the heads were and why they were on that mountain.

Borglum plans a grand hall 80 by 100 feet

Drilled behind the faces,

With an 800-foot-high granite stairway climbing up to it.

At the chamber's grand entrance,

A bronze eagle with wings spanning 38 feet

Sits above huge glass doors.

Inside, bronze and glass cabinets fill the walls,

Showcasing national documents

Like the declaration of independence.

Busts of famous americans decorate the hall,

And the nation's contributions to the world

Are inscribed on the walls.

Gutzon borglum wants to secure mount rushmore's place

Among history's greatest monuments

And america's legacy

For any future civilization discovering it.

Borglum was so attracted to these kind of ideas

Of colossal shrines like the pyramids.

You see from the outside this very monumental structure,

But if you go in the inside, there's this secret chamber

That tell us the story of that time period.

The records show borglum persuades congress

To grant $50,000

For the construction of the hall of records.

In 1938, workers start blasting the cavity for the hall

Out of the mountain.

But world war ii forces a halt.

Congress said, "we need this money for the war effort.

So we're done here.

Don't worry about the hall of records.

Don't worry about the grand staircase.

Just get the heads done."

Narrator: The heads are swiftly completed,

And work on the monument stops in October 1941.

Reed: The hall of records, which had been started,

Is still left there in its unfinished state.

Narrator: There's still evidence

Of the moment that construction stops.

Tool marks scar the sides of the passageway.

In 1998, gutzon borglum's daughter buries

16 enamel tablets in the entrance to the chamber.

This time capsule contains a history of the united states

And biographies of the four presidents and gutzon borglum.

Mount rushmore was intended to be more

Than a tourist attraction --

A high-tech repository to guard many of the national treasures

That defined the history and identity of the usa.

Not all of the seven modern wonders of america

Take their inspiration from the ancient world.

In the 20th century, american engineers

Invent a completely new kind of landmark...

That goes on to change the city landscape

Unlike anything ever before.

And on the other side of the country,

Engineers on the west coast are building another modern wonder,

The golden gate bridge.

How can they make it stand strong

Against nature's deadliest killer?

Narrator: A brand-new class

Of astonishing engineering achievements

Across the u.S.

Outsize the familiar stone and marble wonders

Of the ancient world.

In the heart of manhattan

Stands a spectacular icon of engineering...

...The fourth modern wonder of america,

The empire state building.

The only way to build big in crowded manhattan

Is to build up.

And when the empire state building

Opens in 1931,

It's the tallest building on the planet,

A title it holds for more than 40 years.

Today, it's sky-piercing outline is familiar to billions.

But the secrets to its success

Lie hidden beneath its stone skin.

The skyscraper has a sturdy internal structural framework.

It weighs more than 365,000 tons.

How is such an incredible weight

Supported over such a small area?

The empire state building is actually a slender step pyramid

Widening towards the bottom.

This ingenious shape spreads the weight of the tower

Across more than 80,000 square feet.

Beneath the surface, sturdy steel columns

Firmly lock into huge foundation shafts of solid concrete.

This base is just three stories deep,

52 feet, a fraction of the tower's total height.

How can such shallow foundations support such a massive building?

Geotechnical engineer andrew klaetsch

Thinks the secret lies deep under new york city.

He's at a construction site

For manhattan's newest super-tall skyscraper.

They are excavating right now to build their foundations.

Narrator: Andrew only has to venture 10 feet below street level

To hit the city's bedrock.

And right here is the very surface of the bedrock today,

Right below 32nd street.

Narrator: Other skyscrapers around the world

In london, tokyo, and chicago

Have foundations that are twice as deep,

But new york stands on firmer ground.

Well, what you see here is this rock

That was once buried at great depth

And formed under enormous pressure.

Narrator: This gray rock is called schist.

Klaetsch: It reflects the light.

It actually looks like glitter,

And that is the mica minerals in the manhattan schist.

Narrator: Manhattan schist forms 450 million years ago

When two continental plates collide,

Pushing up vast mountain ranges.

Over millions of years,

The rocks on the surface wear away,

Exposing incredible, strong cores of compressed schist

That manhattan stands on today.

To find out how strong this manhattan rock is,

Andrew takes a sample to his lab.

He uses a compression machine to investigate

How much pressure it can withstand.

Much stronger.

Andrew's colleague lysandra lincoln

Applies increasing pressure

To this 2-inch-thick manhattan schist.

This is the load as it increases with time.

Only up to just over 40,000 pounds.

The sample is holding strong.

Almost 60,000 pounds.

[ boom ] whoa.

[ laughs ]

That was pretty good, pretty explosive.

So you can see, it shattered into many pieces.

This manhattan schist can withstand

A staggering 75,000 pounds of pressure per square inch.

It can safely hold more than 100 empire state buildings.

It's exceptionally strong.

It's significantly higher than any sort of pressure

That we'd be looking at in terms of building foundations.

Once the construction reaches ground level,

The entire structure is finished in just seven months.

It's an astonishing achievement.

The ancient wonders often take decades to build,

But the empire state building surpasses them

In the blink of an eye.

The secret to how this record-breaking

Modern wonder of america is built so quickly

Lies hidden beneath its skin.

The skeleton of the entire tower

Is made from I-shaped steel beams.

They are held together with thousands of rivets...

...And create a massive three-dimensional frame

Of steel boxes.

The workers simply hang the stone facade

Onto the outside like a curtain.

They repeat the same pattern

For floor after floor after floor.

Building nearly a story a day,

They take just 7 months to reach 1,250 feet.

Engineer don friedman

Works with experienced metalworker rich bauer

At a steel forge in new jersey to explore

How the empire state building's steel construction kit

Is pieced together on-site so fast.

Well, right now, we're heating up the rivet

And making sure it gets extremely hot.

Narrator: Rich thinks the humble rivet

Is the real hero of the empire state building.

Bauer: Once you send it all the way home

And make the rivet completely up,

It's not like a nut or a bolt

That's going to loosen up or rattle over time.

Welds could crack.

Rivets, once they cool off, it contracts.

It makes sure that joint is completely tight.

You want a nice, consistent orange.

Narrator: The rivet comes out of the furnace red-hot,

But it takes just seconds for the metal

To become too cool to work.

Bauer: I couldn't set this rivet now.

We'd have to throw that rivet out

And start it over and try another rivet.

Narrator: From the furnace in the workshop,

It takes three people to set a single red-hot rivet

Before it cools.

The construction of the empire state building

Requires an astonishing level of coordination and teamwork.

It's the first time don has seen this process in action.

Friedman: I've read about it, but it's something else seeing it.

Installing rivets requires a team of people

Working together very closely

To make sure that everything happens

Before the rivets cool off.

Narrator: This fast cooling poses a huge challenge

To workers at the empire state building.

They need more than 100,000 rivets

To hold the steel girders together.

To heat the rivets, engineers build furnaces on each floor,

But still, the raw-steel beams can be more than 35 feet away.

Incredibly, workers throw the rivets.

They were trying to throw these rivets

10, 15, 20, 30 feet up in the air,

And they had to make sure they do this

All before it cooled off.

Narrator: Throwing hot rivets solves a problem,

But it's very dangerous.

It took enough skill to do this, and you think about doing it

In the circumstances of actually building a high-rise building,

And it's just incredible.

Narrator: The strong and fast construction

Of the empire state building relies on hot riveting.

The whole building goes up like prefabricated furniture,

A 60,000-ton made-to-order metal framework

Assembled simply on-site.

And as soon as this basic framework is complete,

Other teams can finish each floor.

Workers fill temporary wooden floors with concrete

And reinforce them with wire mesh.

As soon as the floor is set, they lay down railway tracks

To move materials quickly from elevators to the outer edges.

Other teams construct makeshift cafeterias

On the uppermost floors

So builders don't waste time going to the bottom to eat.

Finally, workers at the top simply hang the external walls

On the steel skeleton.

The building soars at a lightning-quick pace.

Innovative building techniques

And clever time-saving solutions like these

Mean the empire state building takes less than 14 months

To build, completing in 1931.

Far faster than the decades

Many of the ancient wonders take to build.

President hoover turns the lights on

From the white house in a spectacular opening ceremony.

The empire state building stands to this day

As an american icon...

...The familiar outline of its incredible spire

Recognizable to billions around the globe.

But why is the building this shape?

What engineering secrets are hidden inside the spire

Of this modern wonder of america?

And at the same time, on america's pacific coast,

The longest ocean crossing ever attempted is under way --

The golden gate bridge.

How do engineers protect it from killer earthquakes?

Narrator: The empire state building

Is the first of the seven modern wonders of america

To top 100 stories...

Far surpassing any of its ancient predecessors.

But what does the empire state building's

Record-breaking height reveal about its forgotten history?

Friedman: We're in herald square, which is one of the busiest

And most crowded parts of the city,

And there's the empire state building

In front of us at fifth avenue.

Narrator: Don friedman believes the empire state building's

Distinctive spire sets it apart in the city's crowded skyline.

With that, you go, "oh. That's the empire state."

Narrator: But this mast also hides a secret.

In 1929, the architects set out to construct

A very different building.

Friedman: This is an early drawing.

There's one thing missing here, which is the spire,

Because this drawing was created

Before the spire was added to the building.

Narrator: The blueprints reveal that empire state building's

Elaborate spire is a very late addition.

Engineers shoehorned it into the design

Only after construction starts.

Why add extra height

To an already record-breaking wonder?

♪

In 1930, the steel-and-glass spire starts to take shape.

At the top, on floor 102,

An observation deck offers breathtaking views.

One floor above is a strange balcony,

With a knee-high wall as the only barrier

To a 1,250-foot drop.

Incredibly, the architects declare

This is for giant airships to dock

And unload passengers directly into the empire state building.

But is this the real reason for the spire?

In the early 1930s, docking an airship with a skyscraper

Is a radical new idea.

Airships don't need runways.

They simply attach to towers or masts using ropes.

Forward-thinking building designers place mooring points

On the top of their structure,

Looking forward to a future of airship-filled skies.

In 1931, airships try to dock

At the empire state building's spire.

It's such a jaw-dropping sight, crowds block the sidewalks

And the busy streets below.

One airship clings on for 3 minutes.

Another drops a bundle of newspapers.

No passengers disembark,

And the attempt is never repeated.

Why is this airship the only one to dock

At the empire state building?

Civil engineer maarten van reeuwijk

Thinks he knows the answer.

He's investigating the empire state building's

Forgotten airship port.

He re-creates the conditions faced by the docking airship

In this wind tunnel at imperial college london.

Maarten wants to find out if an airship could offload passengers

At the top of the world's tallest building.

What I have here is a balloon, which is filled with helium,

And this is going to be a very rough approximation

To the airship, and what I'm going to do is,

I'm going to moor this airship

On the top of the building right here.

Narrator: The tunnel's fans start up.

Maarten adds smoke to see the path of the wind.

So here, you can see the flow as it goes around this airship.

Narrator: The wind that hits the top of the building

Must go somewhere.

It deflects to the building's sides,

But it also goes up.

You see that this highly unsteady flow in the wake

Causes huge response from our airship.

Narrator: The airship and all its furniture, luggage,

And passengers would be hurled around inside.

Van reeuwijk: We're seeing very violent motions of the airship.

Full-scale, these would be ups and downs of the airship

Of 10, 20 meters.

This would be hugely dangerous.

It's not the greatest of ideas to try to moor an airship

On a building like the empire state building.

Narrator: Tall structures like skyscrapers

Can create strong updrafts of wind and unpredictable gusts.

Airships need a second tether to hold their tails in place

And stop them from tipping up in these updrafts.

The tail tether should rotate

And allow the airship to align with gusting winds.

But the empire state building doesn't have this mechanism.

Any airship can only moor for a few minutes

Or drop a bundle of newspapers before moving on.

Tethered precariously just to the mast of the skyscraper,

This is all they can safely achieve.

In 1931, the world's top airship captain,

Germany's hugo eckener, visits new york.

He concludes that any attempt to drop off passengers

At the empire state building would end in disaster.

A few years later, the explosion of the nazi airship hindenburg

Underlines the dangers.

Man: The world's largest and most luxurious airship,

The hindenburg,

Burns in a disaster. [ crowd screaming ]

This tragedy dramatically ends a future era of airship travel.

Narrator: Don believes the real reason for the mast

On the empire state building

Lies with an intense rivalry that grips the city.

People were building taller

And taller buildings in new york.

Chrysler building was the tallest building in the world

For about a year.

By adding the spire onto the empire state building,

It went up about another 15 stories in height.

Narrator: The spire allows the empire state building

To soar above its rivals,

And it protects its record far into the future.

Friedman: Any publicity will help,

And constructing the tallest building in the world

Is one way to get a lot of free publicity.

Narrator: When complete, the empire state building

Is the tallest structure on planet earth.

Towering over every ancient wonder of the world,

It stands as an icon of american engineering,

Ingenuity, and ambition.

Incredibly, at the same time

The empire state building breaks world records,

Engineers on the other side of the country

Are constructing the longest bridge ever attempted --

The golden gate bridge.

But they're constantly under attack

From the very ground they build on.

How can engineers ensure the record-breaking bridge

Can stand firm on the most unstable ground in america?

And below in the bay, another team of engineers

Are busy constructing the most notorious wonder of america --

Alcatraz.

How has "the rock" maintained its unbreakable reputation

Against san francisco's killer earthquakes?

Narrator: The seven modern wonders of america

Herald a brand-new class

Of astonishing engineering achievement...

To surpass the old wonders of the ancient world.

They stand prouder...

Rise taller, and completely transform the landscape.

The fifth modern wonder is on america's west coast,

Here in san francisco...

The golden gate bridge.

The golden gate strait is a mile-wide channel

Between san francisco bay and the pacific ocean.

In the 1920s, the only way to cross the strait is by ferry.

And by 1929, there are 2 1/2 million car trips a year

Across the bay.

The city tasks joseph strauss, an accomplished architect,

To design a bridge to cross san francisco bay

And link it to the city of oakland

On the other side.

But spanning the fast-moving and treacherous waters

Is an incredible challenge

That requires a structure dubbed "the impossible bridge."

To achieve his task, strauss must construct

The most ambitious bridge the world has ever seen --

A two-tower suspension bridge of epic proportions,

The six-lane superhighway

Stretching for more than 1.7 miles,

With the longest span ever attempted,

A masterpiece of bridge engineering.

Work begins in January 1933.

Two colossal towers each weigh 22,000 tons

And stand 746 feet above the water.

They will carry the entire weight of the bridge.

But there's a problem.

The towers sit on a tectonic time bomb.

San francisco experiences killer earthquakes.

Only 30 years before, in 1906,

A massive quake measuring 7.9 on the richter scale

Rips through the city.

Hundreds of buildings collapse,

And over 3,000 people are killed.

More than 80% of the city is destroyed.

The 1906 earthquake is one of the worst and deadliest

In the history of the united states.

San francisco is under constant attack from the earth,

Usually recording 20 tremors a day.

The city sits directly above two colliding continental plates,

Which means another devastating earthquake is inevitable.

Engineers have to make sure the golden gate bridge

Can stand up to the big one.

They sink waterproof walls into the ocean,

Pump out the water, and dig holes deep into the seafloor.

Then they pour in 150,000 tons of concrete

To build mighty foundations rising from the rocks below.

They assemble two 746-foot steel towers on top

And link them with 80,000 miles of steel wire.

Finally, they sink concrete blocks deep into the banks

To anchor the cables

That hold up the most iconic suspension bridge in the world.

In 1989, the city of san francisco is tested again.

A magnitude 6.9 earthquake shakes the city to its core.

Among the damage, the oakland bay bridge partially collapses.

One motorist loses their life.

♪

But the golden gate bridge survives intact.

Earthquakes are terrifying

Because they can strike without warning.

But the golden gate bridge stands tall and confident

Against anything nature can throw at it.

Building the impossible bridge is one of the greatest

Engineering achievements of the 20th century.

It pushes the boundaries of bridge design

And demonstrates to the world

That the usa can overcome any problem that nature can throw.

This modern wonder of america

Spans some of the most treacherous waters

In the country --

Icy cold, 100 yards deep, and full of vicious currents.

These same waters are home

To the most notorious wonder of america --

Alcatraz.

But why do engineers build

The world's first supermax penitentiary in san francisco,

The country's earthquake capital?

Narrator: In only two centuries,

The united states constructs the most extraordinary monuments

To match the engineering achievements

Of the entire ancient world.

Across the continent,

Engineers must overcome the challenges of building

In a wild and untamed landscape.

The sixth modern wonder stands alone,

Surrounded by treacherous icy water

In a deadly earthquake hotspot...

Alcatraz...

A name feared around the world.

♪

Alcatraz stands more than a mile

Out into the waters of san francisco bay,

Its iconic prison block a beacon of crime and punishment.

For decades, this island is home

To the most wanted men in america --

Al capone, machine gun kelly,

Robert stroud, "the birdman."

The convicts that come here cannot be held anywhere else.

What engineering secrets

Lie behind its legendary reputation?

The rock is designed as a prison inside a prison.

The outer wall is over 2 feet thick.

Inside are over 300 cells stacked three stories high.

And a 2-ton steel door blocks the only exit.

Outside, 12-foot-tall fences topped with razor wire,

All surrounded by six tall watchtowers

With guards who shoot to kill.

Alcatraz is the original supermax penitentiary,

But why is the world's first maximum-security prison

Built here?

Most of san francisco stands on land

Reclaimed from the ocean.

The bay mud allows the city to grow,

But this soil is wet and soft.

The 1906 quake turns the ground into quicksand.

More than 28,000 buildings are destroyed,

Including four of the city's prisons.

Lines of evacuated convicts walk the streets,

But the citadel in alcatraz sits directly on hard rock.

The shock waves pass through it,

And it survives the quake with barely a scratch.

Alcatraz is the last functioning prison in san francisco,

So the city ships its prisoners to the rock.

The island's bedrock lays the foundations

For its unbreakable reputation.

Soon after the quake, the iconic prison we see today is built.

In 1934, the island becomes a federal penitentiary,

Home to convicts no other prison can hold.

The authorities are confident

That prisoners are locked up solid on the rock.

But that doesn't stop many from trying to escape.

Any prisoner wanting to break the rock

Has to first deal with solid iron bars in every cell...

Thick concrete walls,

And watchtowers where guards shoot to kill.

But it is the landscape and geology of the rock

That pose the greatest threat to any prisoners on the run.

In 1962, the most notorious escape from alcatraz

Ends in mystery.

Three escaping convicts --

Frank morris and brothers john and clarence anglin --

Stand at the water's edge.

They have an improvised raft made from raincoats.

Freedom is within reach,

But these are treacherous waters.

Draining away the bay reveals hidden dangers.

Across the rocky seafloor

Are caverns and peaks the height of houses

That churn the tides into fast, unpredictable currents

Around alcatraz.

Averaging just 17 feet deep,

The tides sweep the water out towards the bridge,

Where a perilous ravine plummets 360 feet.

It forces 20 times more water through the narrow channel

Than cascades over niagara falls.

Do the inmates overcome these deadly currents,

Or do they get washed out into the open ocean?

Physician dr. Tom nuckton is an authority

On swimming in the bay.

He knows just how dangerous these waters are.

Tom uses this huge scale model,

Built by the u.S. Corps of army engineers,

To chart the men's escape route.

This simulator, just outside the city in sausalito,

Replicates the current in the entire san francisco bay.

Nuckton: This model is really impressive.

You can see alcatraz here, the shallow areas.

Narrator: Tom investigates the tides around alcatraz island

At the time of the escape.

Nuckton: So we can put this boat...

In the water

Right about where we think the prisoners got in the water,

And we can squirt a little dye.

Okay, we have a boat that represents

The raft of the prisoners

And some dye that shows the outgoing tide

That the prisoners would have had to contend with.

Narrator: The currents push the boat

Towards the golden gate bridge.

Nuckton: They'd be swept right out into the pacific ocean,

And you can still see the dye.

Look how quickly it's moving.

Narrator: The model shows the most likely scenario --

The currents sweep the little raft straight out to sea.

Frank morris and the anglin brothers are never found.

The official report concludes

That the men drown after their raft fails.

The rock retains its perfect reputation.

In 1963, alcatraz is consigned to history,

As it closes its doors forever.

But engineers continue to push the boundaries of construction,

And only three years later,

Work begins on the seventh modern wonder of america.

This would be the greatest of them all,

Towering higher than any man-made structure

The world has ever known...

...Rising in downtown new york city, the twin towers.

Narrator: The final modern wonder of america

Is remembered across the globe for its tragic final moments...

...The world trade center twin towers.

The story of their origins is rarely told.

The world trade center twin towers

Are america's most iconic buildings

And her greatest engineering triumph,

But the largest modern wonder of america

Faces huge challenges before construction begins

That test engineers to their limits.

Hidden below the pavement, engineers

Encounter water-logged mud and rubble,

Including a 400-year-old ship preserved in mud.

As they dig deeper, a modern obstacle emerges --

An active railway tunnel

That carries 100,000 passengers per day.

Even further down, 70 feet below street level,

They finally reach bedrock.

This exceptionally hard material is the perfect base to build on,

But here on the southern tip of manhattan,

There's more than 70 feet of soft ground

Between the surface and a suitable foundation.

Structural engineer rick ellman investigates how it is possible

To build a skyscraper on reclaimed land.

Ellman: These tall towers that are all around us,

If they were not constructed properly,

They would lean and very likely topple over.

Narrator: The most famous example of the dangers of unsteady foundations

Is the tower of pisa in Italy.

It is built on marshy land,

Similar to the reclaimed land of manhattan.

Over time, the soft ground causes the tower

To tilt dangerously.

But unlike pisa, manhattan has an incredibly tough bedrock

Below the reclaimed land, manhattan schist.

The twin towers' foundations can be firmly anchored

Into this solid rock, but there's a huge problem --

Reaching it.

Ellman: Excavating in reclaimed land can be a real challenge.

Because of the weak soils and the high ground water,

You're unable to just simply excavate.

Narrator: If they excavate, water and mud just slide back into the hole,

So engineers come up with an ingenious solution --

They create a surrounding wall around the foundations.

The wall acts as a protective barrier.

First, they dig long trenches around the edge of the site

And fill them with a liquid slurry

To stop them collapsing inwards.

Then they drop reinforced steel cages into the trenches

And pump in concrete to displace the slurry.

Once these concrete walls set solid,

Engineers can excavate everything inside them,

Creating a giant underground bathtub.

Instead of holding water in, the bathtub keeps it out

So the foundations can now be built.

They need to create room for 50,000 people

In only 16 acres of land.

So they have to build tall.

Engineers need to push the boundaries

Of what is possible to raise these giants

Higher than any structure the world has ever known

And ultimately create a modern wonder of america

That would be copied across the globe.

What are the engineering secrets

That allow the world trade center twin towers

To soar higher than anyone thought possible?

Narrator: The world trade center twin towers

Is one of the modern wonders of america.

The towers' tragic final moments shake the world to its core.

But their structural genius is often overlooked.

They are america's greatest engineering achievement.

How do engineers push the limits of high-rise design

To build taller than anyone in history?

And why do they become the blueprint

For thousands of skyscrapers that follow?

Japanese-american architect minoru yamasaki

And american engineer leslie robertson

Devise a revolutionary plan to maximize floor space.

Instead of spreading the load across a grid,

Yamasaki creates a super-strong hollow structure.

All the weight is supported around the edge.

It's a breakthrough in skyscraper design.

Each tower is made up of 236 steel columns.

They stand just 26 inches apart around the perimeter.

More than 43,000 windows complete the outer skin.

Inside, steel plates stretch across the void,

Topped with nearly a million tons of concrete

To create 110 floors.

The north tower is crowned with a final feature --

A 360-foot communications mast.

Now they have a new task -- to make this outer skin

Strong enough to support the weight of the tower.

♪

Professor adrian bruegger wants to understand

How the twin towers break the mold of skyscraper design.

Adrian has rare access

To the surviving structures of the twin towers,

Carefully conserved in the basement

Of the 9/11 memorial museum.

He examines the surviving columns

From the outer skin of the building.

So here you can see one of those mega columns

That is landing the forces

From 110 stories into the ground.

And if we look up at the column, we'll see that one of these

Large columns goes through this beautiful trident structure,

Then picks up three smaller columns.

Narrator: The hollow building structure is a breakthrough in engineering,

But this revolutionary concept goes even further,

To the skeleton itself.

This column is actually hollow on the inside,

And that's purposely done

So that we can increase its stiffness.

So the material is all along the perimeter.

Narrator: Not only is the building hollow, but the columns are hollow, too.

Finally the designers use an extra trick

To reduce the overall weight of the twin towers.

The metal is 4 inches thick at the base

But tapers to just 1/4 of an inch at the highest point.

Bruegger: They get lighter and lighter as you go up to the top.

And that is essentially to make the building

As efficient as humanly possible.

So this is how structural engineers

Are able to build this high.

Narrator: Structurally the design is perfect.

It breaks through the constraints

Of contemporary skyscraper building.

With this method, the height seems almost limitless.

The twin towers, revolutionary skyscrapers

That have changed the world forever.

What can we learn from the towers

And the events that lead to their collapse?

The impact of two hijacked airplanes

Creates massive gashes in the towers

And an unprecedented fire that causes them to collapse.

2,753 people die,

But the buildings put up a remarkable fight

In the face of the attack.

On the north face of the north tower

2/3 of the columns were taken out,

But yet the towers stood for more than an hour,

Which allowed occupants

Who were below the floors of impact to escape.

Darton: The death toll was horrific,

But had they not been as well-built or engineered

In the wonderful way that they were,

They probably would have collapsed much earlier

And the death toll would have been exponentially higher.

Narrator: Today at ground level, massive voids

Show the footprints of the towers.

♪

So this is the north tower memorial pool,

And the memorial pools mark the location

Of where the towers stood at the street level of the site.

And here, etched in the bronze parapets,

Are the names of the nearly 3,000 people,

Including my brother, who perished on 9/11.

Narrator: The world trade center's twin towers

And those who lost their lives in 9/11

Are never to be forgotten.

♪

The towers rose on new york's skyline

As a powerful message of american innovation,

Breaking boundaries and reaching higher

Than anyone had ever gone before.

13 years after the 9/11 tragedy,

A new building opens at the world trade center site,

The one world trade center.

Rising 1,776 feet to commemorate the founding of the nation,

It is new york's new tallest skyscraper.

♪

In just two centuries, the united states of america

Has matched the size, scope, and ambition

Of the original seven wonders of the ancient world...

...And has set new standards

For the ultimate achievements of humanity.

Building taller, longer, and higher,

The american people have tamed the wild geography

Of this extraordinary new continent

To build seven modern wonders

That help to define the identity of the united states of america.

-- Captions by vitac -- www.Vitac.Com

Captions paid for by discovery communications

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