Original subtitles

- [Narrator] The world's greatest structures,

push the boundaries of engineering.

All fueled by a constant desire to innovate.

- Without engineering, there would be no modern world.

- [Narrator] Gigantic buildings,

complex infrastructure,

and ingenious inventions.

- Engineering is the key that turns dreams it's reality.

- [Narrator] Many of today's incredible achievements

rely on breakthrough technologies,

first devised by ancient engineers.

- It's astounding how they achieve this.

- [Narrator] Early civilizations built

on an unimaginable scale and with incredible precision.

- They raised a 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 they're genius

laid the foundations for everything we build today.

[exciting music]

Today, across the planet,

countless engineering marvels for antiquity still stand.

- We wonder the great engineering marvels,

the great engineering technologies that are all around us.

- [Narrator] The Great Wall of China,

traversing over 13,000 miles through arduous terrain.

Machu Picchu, built impossibly high

atop of Peruvian mountain.

The Coliseum.

Capable of holding over 50,000 roaring spectators.

- History is about cultures, about people who create things,

who are then overthrown and forgotten,

but then rediscovered.

- [Narrator] These achievements

have rightfully claimed their place in history.

Yet for every pyramid, Pantheon, or Parthenon,

there are lesser known achievements

that also deserve recognition.

- Every year, we uncover new ancient engineering

that adds to that narrative that we have

about what engineers of the past could achieve.

- [Narrator] The invisible effects of technology,

which either lie underground,

are hidden beneath the surface of the architecture,

or are only perceptible with senses other than sight.

- We may find it in monumental form,

we may find traces of it,

but it is part of the story of humankind.

- [Narrator] Hidden innovations

that also employed precision engineering,

to underpin incredible achievements.

- So much of what ancient engineers have achieved

has flown under the radar.

These are history's hidden marvels.

- [Narrator] For 2 million years,

our earliest ancestors lived life constantly on the move.

- Primitive societies would've relied for sustenance

on gathering and hunting.

So a mixture of berries, fruits, nuts, seeds,

as well as hunting wild animals.

So when they've exhausted supplies in one area,

they'd be moving onto another area.

- [Narrator] But then around 12,000 years ago,

came a development that would change everything.

Agriculture.

First emerging in the Middle East

in an area known as the Fertile Crescent, by 6,500 BC,

the so-called neolithic revolution

saw agriculture arrive in Europe.

And for the next two millennia,

it swept across the continent from east to west.

- Across the inhabited world,

people started settling down planting crops and staying put,

and that led to people building houses, villages, towns,

cities, civilizations.

- [Narrator] The new sedentary, agricultural lifestyle

brought a steadier, more predictable supply of food.

But it also introduced new challenges

for those early farmers.

- Hunter gatherers take water from the stream or pool

where they happen to be, and then move on.

But if you are a farmer, then you're tied to the land,

and you had to find a way of ensuring

that water supply was always available.

- [Narrator] Many early settlements were established

near streams, rivers, or lakes.

But in more arid environments, or during periods of drought,

some neolithic communities tapped

into a different source of water altogether.

- Hidden below the ground is what's in as groundwater.

Rainfall is trapped typically in a layer of clay.

So it's possible to dig a well down

to that particular level.

And it will naturally fill with water

that can be drawn on a reliable basis.

- [Narrator] Wells were bored into the ground

at depths of up to 45 feet.

But these deep holes filled with water,

were structurally weak and prone to collapse.

- In order for these wells to survive,

it was necessary to line them in such a way

to hold back the earth from collapsing.

And various materials had been used throughout history,

stone, and brick,

but these neolithic farmers used timber.

- [Narrator] The remains of over 100 neolithic wells

have been found across Europe.

In 2018, during the construction of a motorway

in the Czech Republic,

one extraordinary discovery transformed the modern view

of just how far back in time these structures were built.

[thrilling music]

It has become known as the Ostrov Well.

- What's remarkable about this well lining,

is that it was dated using dendrochronology,

which is where we look at the sequence of tree rings

to give us an absolute date of construction.

And in this example is 7,278 years old.

And that makes it the oldest wooden structure in the world

to be dated using this method.

- [Narrator] Existing at a depth of five and a half feet,

this ancient timber lining helped to ensure

that the collected groundwater did not silt up.

- It's really tremendously early,

thousands and thousands of years before the Greeks

or the Romans or other civilizations.

- [Narrator] Made from oak,

it's not just the well lining's great age

that is impressive.

The sophistication of the carpentry skills

needed to construct it are also exceptional.

To form the box-shaped lining,

longitudinal mortices were cut at 90 degree angles

into four vertical oak corner posts.

Seven planks, each with end tenons,

were then inserted horizontally

to create a structure measuring

about four and a half feet high,

and two and a half feet wide

that stabilize the walls of the well.

- But these neolithic farmers only have had

polished stone axes to build these wells with.

- And the level of preservation is so good

that we can see the problems that they had

splitting the timber and dressing it down

without metal tools.

- So what is incredible is how they're able

to achieve really very sophisticated jointing.

It is an absolute marvel of carpentry.

- [Narrator] The hidden genius of well linings,

like the one at Ostrov, allowed neolithic settlements

to thrive right across Europe.

And set in place a method of construction

that would be adopted by civilizations

throughout the continent.

- And these well linings that they may seem simpler,

are a really good technological solution

to provide a stable water supply to a growing community.

They wouldn't have survived without it.

- [Narrator] Almost 5,000 years later,

another extraordinary piece of engineering

would underpin the success of a major civilization

in the parched deserts of the Middle East.

Ancient Persia.

Now Iran, a place where art, science,

and literature flourished.

It was the heart of the Achaemenid empire,

founded in the sixth century BC by Cyrus The Great.

- Cyrus The Great, creates not just an urban culture,

but also has incredibly successful army,

constructs roads, builds palaces, introduces coinage.

All the features that we see really in a modern empire.

- [Narrator] By 475 BC, it was one of the world's

dominant powers stretching all the way

from Egypt in the west, to India in the east,

and is recognized as one of history's earliest

great empires.

Much of Persia was situated in a scorching desert landscape.

Perilously dry in summer, sometimes receiving

less than four inches of rainfall each year.

Not even one quarter of the global average.

Survival was far from a given,

but even with temperatures often soaring

above 100 degrees Fahrenheit,

the Persians succeeded in developing highly sophisticated

agricultural processes.

- They had to produce enough food to feed the army

that supported this great empire.

They did this by using a type of underground channel

known as a qanat.

And this brought the mountain waters

down into the planes so that they could have

irrigated fields and able to grow wide range of crops.

- [Narrator] Their agricultural prowess

produced an abundance of food.

However, successfully storing and preserving

this produce for any length of time

during the intense heat of summer, proved problematic.

Desert engineers had to find a solution

or the population would starve.

- Preserving food in a hot environment is a challenge.

Societies have found many different ways of doing that.

You can dry things, you can smoke them.

- But the person's also siphoned off some water

in these hot, arid deserts and turn it into ice.

- [Narrator] Producing ice in the desert heat

may seem counterintuitive,

but it's thought that by 400 BC, ancient Persians

found a way to capitalize on one aspect

of the harsh climate they lived in.

- We have to remember that in this area,

while the deserts can be very hot during the daytime,

at nighttime, they can drop to as low

as 20-22 degrees Fahrenheit.

- [Narrator] Their groundbreaking invention was a Yakhchal.

Meaning ice pit, this conical-shaped structure

measured up to 60 feet high

and covered a deep hollow dug in the desert sand.

The walls, up to 6.5 feet thick at the base,

were made from a local material called sarooj.

Consisting of sand, lime, clay,

egg white, goat hair, and ash.

The domed Yakhchal, was built next to a large shallow pond,

which was fed with water from a qanat.

A high wall shielded the pond from the warmth

of the low winter sun in the daytime.

And during the colder nights, the water would freeze.

The ice was then broken up and transferred

into the pit below the beehive-shaped Yakhchal.

Its thick walls helped insulate the ice

from the intense heat of the desert.

And the shape of the structure encouraged

warmer air to rise and escape through a hole in the top.

- Studies have calculated that of the ice made

in the winter,

probably around 80% would still be there in the summer.

And that's an example of incredible thermal efficiency.

- [Narrator] Remarkably effective,

the Yakhchal system could produce ice

on an almost industrial scale.

- These could be very sophisticated

and actually very large structures.

And some people have estimated they could store

the equivalent of about 3 million modern ice cubes.

- [Narrator] As well as helping to preserve food,

ice could also be used to chill desserts, like sherbet.

- The primary use of the ice I'm sure,

is for keeping food fresh and cool in the summer.

And if you are very rich and powerful,

you might also take a block of ice

and use it to cool down part of your house,

as sort of early air conditioning.

- [Narrator] There are a rare few surviving Yakhchals today.

Over the centuries, most were eroded

by destructive desert storms.

But this ancient technology allowed the Persians

to prosper and survive in the desert for centuries,

making it a true marvel of engineering.

- Their genius was to bring together

what we now understand through physics,

but they must have known through practical knowledge

about how to create ice, how to control thermal currents,

how to insulate buildings.

They brought all together to construct

these incredible buildings.

- So when we think of the kingdoms and empires of Persia,

we might think of the great palace buildings,

and rock cutter scriptions,

hidden marvels like these Yakhchals,

actually underpin and make possible

the day-to-day living that made the empires

and the civilizations exist and thrive.

- [Narrator] Throughout history,

the clever management of natural resources

has been key to the success or failure

of people's and powers.

And almost 1,000 years after the birth

of the Yakhchal in Persia,

another major civilization beat the odds to provide water

to its citizens and build one of the greatest empires

the world has ever known.

[tranquil music]

Istanbul, Turkey's largest city.

Today, the economic, cultural and historic hub

of this vast country.

But for centuries, it was known as Constantinople,

and was at the very center

of the longest lasting medieval power,

the Byzantine empire.

Holding sway from the fourth to the 15th centuries,

the empire was at its largest in the sixth century,

when it stretched from Italy and the Balkans,

to Turkey through North Africa,

the Middle East and Southern Spain.

At its heart was a bustling metropolis

with a population of up to half a million people.

- Constantinople is located at the point

in which Europe meets Asia.

Is literally the place in which the trade routes

east and west converge.

- Location is everything for an ancient city.

And it was a point through which great caravans

of wealth and trade flowed,

it's in a very strategically significant location.

- [Narrator] Constantinople also had a natural harbor,

and it soon became a busy and prosperous port city.

But there was one crucial downside to its prime location.

- It's surrounded by water, but it's surrounded by sea.

You can't drink it.

And it's an area with harsh winters with dry summers.

- Getting hold of fresh water

and having a constant supply of fresh water,

that posed a problem for a city

that was really looking to grow.

- [Narrator] Their solution was to build aqueducts,

lots of them.

By the middle of the fifth century,

they had constructed a system measuring

over 260 miles that delivered fresh water to the city.

But despite this substantial infrastructure,

the city's water supply continued to run dry

in the hot summer months.

- So the solution, when you've got just seasonal water

coming into your city,

was to build some form of storage.

And they did this through systems,

huge underground storage pits,

lined to keep fresh water clean so that they had access

to it throughout the course of the whole year.

- [Narrator] Fed by aqueducts,

more than 200 subterranean sisters existed across the city.

Even some of the smallest could hold a body of water

weighing more than 10 tons.

But there was one hidden beneath the metropolis,

which out-shone all the others in both scale and beauty.

The Basilica Cistern.

- It's an extraordinary place to visit.

You go down these little steps underground

and there's that "wow" moment

when you see this forest of columns.

It's more the experience of a cathedral

than it is of a cistern.

- [Narrator] Built around 532 AD,

the Basilica Cistern measures 450 by 210 feet,

and could hold over 20 million gallons of water.

But that enormous capacity presented significant challenges.

- And it has to withstand the enormous weight

or pressure that that volume of water will exert

on the walls of the system.

- [Narrator] 25-foot thick walls countered this pressure.

While the roof is supported using 336 marble columns,

each up to 30 feet tall.

- Not only was it able to hold up this enormous bulk

of water, but the columns themselves supported a vaults,

which then supported a considerable thickness

of ground above.

But when you look at the individual columns,

you realize that every single one of them

is slightly different.

- [Narrator] The most spectacular are carved

with a Medusa's head.

Their origin is unknown, but they're thought

to have been built from materials

from destroyed Roman cities and brought in by sea.

- And incredibly, it carried on being used

over a thousand years as a functioning system,

without any need for repair.

- [Narrator] Built close to the palace

of the Byzantine rulers,

it's likely that the water from the Basilica Cistern

was used by the city's elite.

A clue perhaps to just why so much effort

was put into this largely hidden structure.

- You could be walking around the street,

you've just come out of the great Hagia Sophia next door,

and little do you know that actually hidden

below your feet, is an equally impressive

engineering marvel.

- And without it, Constantinople,

which was the capital of this great empire,

one of the most important civilizations

in this part of the world,

would not have been able to function.

- [Narrator] The impressive columns of the Basilica Cistern

carried the weight of the city above them,

supports of a very different kind,

underpins some of the most extraordinary

contemporary structures ever built.

Despite today's exponential growth

in green and renewable forms of energy,

oil and gas production remain at the heart

of the world's energy supply.

Offshore drilling accounts for around 30% of production.

And there are more than 12,000 oil and gas rigs

in oceans across the globe.

Often positioned in the center of hostile seas and oceans,

anchoring these colossal structures to the sea bed

called for some very innovative engineering.

- Exploring for oil and gas in the open sea

is incredibly challenging. The environment is treacherous.

There's wind, there's rain, there's waves,

there's the ocean swell, and if you don't get it right,

there could be catastrophic failure.

- We think we've experienced storms on land,

but the force of a marine gale

is something entirely different.

Whatever tries to remain static,

those forces will try to move and can even destroy.

- [Narrator] The North Sea.

Covering an area of 220,000 square miles

and hemmed in by Great Britain to the west,

Continental Europe to the south,

and Scandinavia to the east.

184 offshore rigs drill for oil and gas

in this region alone.

And 50 miles off the west coast of Norway,

lies one of the most impressive,

the Troll A gas platform.

At over 1,500 feet in height,

it stands taller than the Empire State Building,

making it one of the world's largest gas platforms.

This is an astounding structure,

two thirds of which is below the waterline.

And the story of its construction

is a marvel of hidden engineering.

- When they were building the Troll A,

they faced numerous engineering challenges.

Firstly, the legs had to reach almost a thousand feet down

if they were going to touch the sea bed.

At the top of these legs,

they had to withstand battering by waves.

But at the bottom,

there was pressure of 500 pounds per square inch.

- [Narrator] Because of this significant pressure,

choosing the right material with which to construct the legs

was crucial to the survival of the platform

and the often raging waters.

- Their solution was to reinforce the concrete

with steel girders, which allowed it to withstand

a bending motion whilst also retaining

that inherent strength.

- [Narrator] One challenge overcome,

engineers face the next;

attaching the legs to the rig's platform.

Assembly in the treacherous open sea

would've been impossible.

So the sections were joined in the calmer waters of a fjord.

- An extraordinary engineering achievement up to now,

but the best was yet to come.

They floated it across the North Sea

until it was into position.

A really extraordinary achievement.

It's the tallest structure that has ever been moved by man.

- [Narrator] Upon reaching its final position,

the structure was sunk to the point

where the legs touched the sea floor.

- But once it was there, how is it fixed in place?

How do you make this thing immovable

against the force of the ocean?

- [Narrator] When the hollow concrete legs

are ballasted with water, the entire structure weighs more

than the Golden Gate Bridge.

But even this enormous weight wasn't enough

to fix the rig securely to the sea bed.

So engineers came up with an extraordinary hidden solution

that took advantage of discoveries

in the power of air pressure made more

than 350 years ago by German inventor, Otto von Guericke.

- They were fixed to the seabed,

not with a mechanical fixing,

but through using suction.

Now, if you think of how you have a glass of water,

and you pull it out of a basin or a bath, for example,

you can feel the force trying to pull it back down again.

And that's the principle used here,

just magnified many times over.

- [Narrator] An ocean bottom fastener,

known as a vacuum anchor, breathed new life

into a century's old idea.

At the base of the rig's legs,

there are a series of 130-foot cylindrical-shaped

vacuum anchors with an open end facing the sea floor.

A valve at the top of each anchor is opened

allowing the enclosed water and gases to escape

as the anchor is sunk into the mud.

The valves are then closed.

And whenever the motion of the sea applies

a lifting or sideways force to the legs,

the vacuum increases inside the anchors

effectively sucking them to the floor

and securing the entire rig.

- None of us will ever see this system working.

It's a piece of hidden engineering, a leap of logic,

a piece of genius operating a thousand feet under the waves.

- [Narrator] The Troll A gas platform

has been in operation since 1996,

and has endured the impact of 2.5 million waves a year.

Some up to 98 feet high, and has stood firm

against the power of hurricane force winds

in excess of 100 miles per hour.

- This isn't just one engineering achievement,

it's a whole series of engineering achievements.

Each one of which almost defies belief.

- [Narrator] Throughout history,

some of the most stunning architectural achievements

have been underpinned by a hidden piece

of inspired engineering.

And one of these pivotal innovations

came in the third century AD,

when Persia the then most powerful empire in Asia,

began a brave new chapter in its history.

The birth of the Sasanian dynasty.

- The Sasanians were incredible.

They're contemporary really with the Roman empire,

though an Eastern version of it.

- From the third to the seventh centuries,

they saw massive achievements, both in urban development,

but also architecture and construction.

- [Narrator] And one of the most iconic features

of their architectural style

was a feature borrowed from the Romans.

The dome.

- Sasanians took the Roman form of the dome

and developed it and made it their own.

And you can see why they did it.

They found it particularly suited to religious buildings,

because for them it was a kind of perfection.

It was a divine form because it emulated

the sphere of the skies.

- [Narrator] Visually impressive,

the dome is also an extraordinary piece of engineering.

Its spherical vault is entirely self-supporting,

allowing it to span large areas

without the use of columns or beams

to create an open space below.

- All of the weight and the forces

travel evenly through the depth of the dome

onto the structure that supports them.

So they hold their own weight.

- [Narrator] Adding a dome to a circular building,

is relatively straightforward.

As the forces are distributed evenly

through the structure below.

But ever the innovators,

the Sasanians wanted to add them to square buildings too,

but it presented both their architects and engineers

with significant challenges.

- But immediately, you want to put a dome

over a square or rectangular building,

the dome is exerting forces on the middle of the walls.

While at the corners,

the dome remains completely unsupported.

- [Narrator] So ancient engineers needed to find a way

to cap buildings with substantial domes

in a way that wouldn't cause

the entire structure to collapse.

- What you need is something that can transform the load

coming through the dome and distribute it in a way

more evenly down to the rectangular structure.

- [Narrator] The solution that the ancient Sasanians

came up with, was an innovative,

and rarely celebrated piece of engineering.

- Marrying up a square room to a round dome

was solved through squinches.

- [Narrator] To distribute the dome's weight

evenly through the base, squinches are shaped.

Transitionary features were built

across the interior corners of the building.

This transformed the square, or rectangular shape

of the top of the structure, into an octagon.

Meaning the forces created by the weight of the dome,

were distributed more evenly

through the walls supporting it below.

- The squinch sounds like a technicality,

but it's a kind of hidden technology,

because we just take it for granted.

Without that leap of logic,

then the Persian empire wouldn't have developed

the architecture of domes,

which is really one of the great glories

of world culture today.

- [Narrator] One of the oldest examples of a Persian dome

that utilizes the squinch is found

at the palace of Ardashir in Iran.

It was built in the third century AD,

using cobbles embedded in mortar.

- The Sasanians were the experts in building

this type of domed architecture.

And shortly after the invention of the squinch,

this area of Persia was invaded by the Muslim armies,

who saw this fantastic type of dome construction.

And it was then adopted almost

as the signature architecture of Islam.

- [Narrator] And it was during the Islamic Golden Age,

that a stunning variation on the squinch emerged,

the muqarnas.

First appearing in the 10th century

in Iran and North Africa, it is a purely decorative feature.

It's complex 3D geometric patterns

designed using little more than compass and ruler,

were used to smooth the visual transition

from straight walls to domed roof.

- It is, you know, an absolute marvel,

and without the squinch,

we would not have the amazing domed architecture

of the Islamic world.

- [Narrator] The humble squinch,

sewed the seeds of an architectural revolution.

And over the centuries, the dome continued to develop.

Culminating in the construction of what would remain

the largest cathedral in the world for almost 1,000 years.

The Hagia Sophia in Istanbul.

The building's most prominent dome,

achieved its impressive dimensions

by utilizing the successor to the squinch.

- The Byzantine empire,

they were also experimenting with dome structures,

but there they used a different form of stabilization

known as the pendentive.

- [Narrator] Essentially, a spherical triangle

that serves as an arch.

This more complex version of the squinch

provided abundant space for decoration,

and is still in use today.

The dome remains an intrinsic feature

of modern architecture.

And one in particular became emblematic

of perhaps the most seismic event in 20th century history.

In the German capital, Berlin,

an iconic building has come to symbolize new beginnings

in the country's often turbulent history.

And stands as a landmark on the city skyline.

After its opening in 1894,

the Reichstag became the home

of the German Federal Parliament

during the late Imperial Period,

and through the Weimar Republic.

- Most famously of course, it survived the second World War.

There's a very famous photograph of Russian troops

raising a flag on top of the building

once they'd taken Berlin.

- [Narrator] When the war ended, Germany was split in two;

the Western half a democracy,

the Eastern, a communist state.

In the early sixties, a wall was built

physically dividing the city.

By this time, the parliament had already moved to Bonn,

leaving the Reichstag with no significant role

for more than a quarter of a century.

- As a consequence of the division of Germany

into east and west, this building's kind of

without function and without purpose.

So for a building that had been so prominent in the empire,

it had really quite an ignominious fall from grace.

[lighthearted music]

- [Narrator] But 44 years after the end of World War II,

came the most seismic moment in modern history.

[people cheering]

When events unfolded, that would change the fate of Germany,

Berlin and the Reichstag itself.

- In 1989, the Berlin wall comes down.

And this is a really important moment for European history,

because by October, 1990,

east and west Germany have become reunified.

- It was a new beginning for the country,

and it was decided that the seat of this new democracy

would be moved to the Reichstag in Berlin.

- [Narrator] After decades of division,

a now reunified Germany wanted to mark this moment

of renewal and the Reichstag,

originally built with a dome that was destroyed

by fire in the 1930s, was to be restored

to its former glory,

but with a state-of-the-art edition.

- So what they decided to do is to put in place

a new glass dome.

And this was seen as a sort of symbol

of the new transparent democracy

that Germany was to enjoy from then on in.

- [Narrator] The new dome was 131 feet in diameter

and 77 feet high.

But adding a modern structure to an old building,

required innovative engineering solutions.

- When you're retrofitting a historic building

and adding new parts, you've got all sorts of problems,

not just of design, but of construction.

- [Narrator] Just as the Sasanians had done

in centuries passed, the engineers of the Reichstag dome

used a transitional feature called a box girder,

on the top of the building.

24 art-shaped steel ribs were then added

to the circular girder to form the shape of the dome.

The ribs house hinges, supporting pedestrian ramps,

which afford visitors a 360 degree vista of the city below.

As architecturally striking as it is,

the dome still had one major practical issue.

- The problem is, is you create a big iconic dome like this,

but you are also creating a glasshouse.

And glasshouse means heat.

So you also have to have an incredibly innovative system

of circulating air around it,

just so people inside it don't cook off.

- There were two solutions to keep the building below cool.

Firstly, there is this solar shade,

which electronically tracks the movement of the sun

to block direct sunlight.

And secondly, there are gaps in the glass panes of the dome,

which allows rising heat to escape. So natural ventilation.

- [Narrator] The new Reichstag dome was completed in 1999,

and the German Parliament took a permanent residence

in the building in September of that year.

- It's a beautiful, modern reinterpretation

of a fantastic engineering design.

- [Narrator] An exquisitely engineered juxtaposition,

the dome has become one of the most symbolic structures

in all of Germany

Today, discoveries continue to be made,

which shed new light on concealed innovation

in ancient technologies,

which culminated in extraordinary engineering.

In 12th century, Ethiopia, King Lalibela

ordered his people to construct a series

of 11-below ground churches,

all literally hued from solid basalt.

In the meso-American city of Teotihuacan,

in the first century AD,

the massive Pyramid of the Sun

was constructed as a monument to the environment

that surrounded its people using little more than earth.

While in the 12th century,

high in the Andes mountains of Peru,

the Inca were establishing themselves

as one of the great south American civilizations.

But in order to farm, often at heights over 10,000 feet,

the Inca constructed two and a half million acres

of terraces.

And at one location in Moray, the temperature difference

between the top and bottom levels

can be as much as 27 degrees Fahrenheit,

leading to an astonishing conclusion.

- The identification of these different micro climates

has led researchers to believe that the Moray terraces

are actually an ancient agricultural research station.

- So you could test what crops would grow

at what level of altitude,

and this enabled the Inca to experiment

with all types of crops, and to really expand

their range of agricultural development.

- [Narrator] Over 1,500 years prior to the end

of the Inca empire,

on the other side of the world,

Greecian engineers had found a completely different purpose

for another circular form within the natural landscape.

[exciting music]

The ancient Greeks, brilliant mathematicians,

artists, and philosophers.

And creators of one of the most impressive buildings

of antiquity,

the Parthenon.

Constructed in the fifth century BC

to honor Athena, the Greek goddess of war,

its marble columns still dominate the Athens skyline

almost two and a half thousand years later.

But it's not the only work of Greek architectural genius

to have survived the ravages of time.

Southwest of Athens, lies the Peloponnese.

A mountainous peninsula of more than 8,000 square miles

jutting into the Mediterranean Sea,

and home to a marvel of ancient engineering,

which is a feast for both the eyes and ears.

The Theater of Epidaurus.

- The ancient Greeks love drama.

They invented tragic drama, comic drama.

So wherever the Greeks went, they built theaters.

I think the first impression you'd get as a visitor

is how beautiful this building is.

It has a sort of grace and symmetry

and it's part of a very beautiful natural landscape.

- [Narrator] Constructed in the fourth century BC,

the Theatre of Epidaurus could seat up to 14,000 people,

and was used for performances for over 500 years.

But it's not just its incredible architecture

that sets it apart.

- A hidden feature of this theater

is how well it's engineered for sound.

- You can hear everything that happens on stage

with immense clarity, wherever you are sitting down.

- [Narrator] Recent tests have shown

that sound at the theater can be heard almost perfectly

at a distance of 195 feet from the stage.

But delivering such exquisite acoustics

is a delicately engineered balancing act.

When sound is generated,

it propagates in waves from its source to the listener.

The first waves are called direct sound.

Sound waves that bounce off surrounding surfaces once,

and reach the listener fractionally later,

are called first reflections.

And finally, the sounds that bounce off multiple surfaces,

usually walls and the ceiling,

reach the listener last and are called late reverberations.

Good acoustics depends on getting the combination

of direct sound, first reflections,

and late reverberations just right.

- You have to keep in mind that Theatre of Epidaurus

is an open structure.

It doesn't have a ceiling.

So you only have direct sound,

and some early reflections, no late reverberation.

You only have two of the three elements for good acoustics.

And yet, it still manages to have great acoustics.

- [Narrator] So how did the architects of Ancient Greece+

engineer near-perfect sound so long ago?

- The most effective way to ensure that sound reach

from the stage to the audience is to channel

and reflect that sound using the shape

of the theater building itself.

This concave bowl of seats in a fan-shaped array

heading up the hillside, helps to funnel

and direct the sound and keep it within the audience area.

- Because of that, the audience had a direct sideline

to the actors on stage.

And so the sound was unobstructed

in its propagation from stage to the audience.

- [Narrator] In 2007,

researchers from the Georgia Institute of Technology,

pinpointed another design feature that may have helped

its architects achieve such amazing acoustics.

- They believe that the very regular pattern

of the seats and the specific distance

between one row and the other,

act as a acoustic filter.

- [Narrator] Studies concluded

that the seats filter low frequencies,

thereby increasing the relative proportion

of high frequencies, on which hearing

the human voice clearly, is dependent.

- This acoustic filtering effect makes sounds clearer

and more intelligible.

And this is the stunning example of acoustical engineering.

- [Narrator] There can be little doubt that ancient Greeks

created a beautiful theater,

and an almost acoustically perfect performance space

at Epidaurus.

But where the hidden marvels of its design

an exquisite feed of engineering, or a happy accident?

- Whether they understood the signs of acoustics

as we do are rather down,

but they knew what worked, and they had enough experience

and practical knowhow to ensure

that the way they built their theaters

suited the need to hear very clearly

what the actors were saying.

- [Narrator] Whether intentional or accidental,

the theater's combination of architectural beauty

and exceptional acoustics,

is a triumph of ancient engineering

that influenced the design of theaters

for centuries to come.

It's such an impressive feat,

that even world-class architects of the modern era

have found it difficult to replicate.

The Sydney Opera House, famed for its groundbreaking design,

architectural innovation, and soaring sail-shaped shells.

But hidden beneath its world-famous facade,

is a dramatic story of complex engineering challenges

and extraordinary solutions.

- While we marvel at these great technological achievements,

they're often the product of a much lesser known process

of experimentation.

Without which, these great engineering structures,

they could not have been created.

- [Narrator] The Sydney Opera House

was the brainchild of Danish architect, Joørn Utzon.

But such an ambitious project,

brought with it considerable challenges.

Many believed his radical design could never be built.

Incredibly, it wasn't until two years

into the construction of the foundations,

that Utzon finally solved how to actually construct

the complex shape of the buildings outer shells.

- He came up with his solution when he realized

that all the shapes of the sail could be created

from one piece of geometry, a sphere.

Which meant segments could be pre-fabricated.

- [Narrator] This avoided the need for expensive form work

by allowing the use of pre-cast segments,

which could be more easily formed

because of the ease of repetition.

Utzon's insight is known as the spherical solution,

and is recognized as a timeless expression

of the fusion between design and engineering.

Despite this significant breakthrough,

Utzon was forced to resign halfway through construction,

due to ongoing delays and spiraling costs.

His replacement, Peter Hall,

oversaw the building's completion.

But Utzon's spectacular original interior design

was never realized.

And the acoustics in the concert hall

fell short of expectations.

- There are too many issues.

The orchestra can't hear each other and themselves

as well as they should.

And the sound that reaches the audience lacks power.

- The concert hall is a space built for music.

As beautiful as the architecture might look,

getting the acoustics right is crucial.

- [Narrator] The beautiful, but awkwardly shaped hall,

and it's partially vaulted ceilings

created unwanted reverberation.

- So they installed an array of ring shaped

hollow reflectors hanging above the stage.

- [Narrator] Each of these 21 reflectors

measured around six feet in diameter.

And because of their distinctive shape,

they became known colloquially as the donuts.

Only ever intended to improve the balance of sound

for the musicians in the orchestra pit,

they weren't as effective as hoped.

- Over decades, acoustical engineers tweaked the design

and the arrangements of this donut reflectors.

But in spite of the effort they didn't work that well,

probably because the area covered by those reflector

was not sufficient.

And also the round shape was scattered sound too much

as opposed to create very focused,

loud reflections on stage.

- [Narrator] The ongoing problem of poor acoustics

for the audience remained even harder to solve.

- The main issue is that the lightweight structure

of the building is not capable of containing

low frequencies in its interior.

Therefore, the reverberation time at low frequencies

is very poor.

As a consequence of that,

the sound of the orchestra doesn't sound as rich

and full as it should.

- [Narrator] In an attempt to finally resolve the issues,

in 2020, an extensive two-year

multimillion-dollar refurbishment of the hall began.

This saw the famous donuts removed

and replaced with paddle-shaped fiberglass reflectors.

- This will improve early reflection

and ensure that musicians can hear than self quite clearly.

And also the audience will receive much greater amount

of early reflection and that will improve clarity of sound.

- [Narrator] Newly designed wooden reflectors

were also installed on the walls,

as well as extensive adjustable acoustic drapery.

- This in combination with a state-of-the-art

electro-acoustic system, will enable the concert hall

to be quickly adapted to different genres of music,

from amplified music to classical.

- [Narrator] To celebrate 50 years

after it first opened its doors,

the stunning architecture of the Sydney Opera House's

exterior may finally be matched by world-class acoustics

inside its concert hall.

Through the ages, our ancestors' astonishing drive

to innovate has propelled the march of history.

And seeing humankind develop from hunter gatherers

to establishing immense civilizations.

- The human story is one that is indexed

incredibly closely to feats of engineering

as we've confronted the various challenges of the day.

- [Narrator] But often, some of the incredible technology

that contributed to the success of their creations

remains hidden or buried by the sands of time.

- So much ancient engineering is already known about,

but in reality, it's just the tip from iceberg.

- [Narrator] What other jaw-dropping engineering

marvels lie hidden?

Only time will tell.

- No doubt will continue to be surprised and amazed.

[exalted music]