Original subtitles

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- [Narrator] Throughout the ancient world,

architectural giants have embodied

the extraordinary ambition of their builders.

- This is one of the most intriguing structures

in human history.

- [Narrator] The vast Colosseum reveals

sophisticated ancient Roman engineering techniques

used to showcase unparalleled displays of power and specs.

- There were amphitheaters all around the Roman Empire,

but this one was the greatest of them all.

- [Narrator] But does the true key

to its success lie hidden deep beneath the earth?

Clues hinting at innovative materials

and building methods used in the construction

of the Great Wall of China,

still linger in its serpentine expanse.

- Stretching over 21,000 kilometers.

The Great Wall is the longest manmade

structure in the world.

- [Narrator] What unexpected ingredient

may have helped cement its strength.

Within the imposing structure of Malbork Castle,

Lies strategic design and construction methods

that allowed it to claim the title

of the largest brick fortress in the world.

- The castle's design incorporated

multiple layers of defense,

each one more challenging to overcome than the last.

- [Narrator] But what enigmas does it hold within

or perhaps beneath its defensive walls?

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In the eternal city of Rome,

the Colosseum stands as a symbol of an ancient empire's,

relentless pursuit of grandeur.

It's weathered stone still resonating with the echoes

of gladiatorial combat and the roar of the crowd.

- I think the Colosseum represents

sort of the greatness of Rome.

When you think about the Roman Empire,

most people automatically think of the Colosseum

and the fact that it's still standing

after all this time, I think makes it so appealing

and interesting and inspiring to people.

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- [Narrator] Though time, nature and vandalism

have claimed nearly two thirds of the ancient structure.

Its surviving walls stand as a testament

to its former splendor.

- It sprawls across an impressive six acres,

raiding as the largest amphitheater ever built.

- [Narrator] Spanning an impressive 189 meters in length,

and 156 meters in width.

The Colosseum's oval shape consists of four stories

with its highest point reaching a towering 48 meters,

boasting 80 entrances, it's estimated

that it could hold between 50 and 80,000 spectators.

- The design of the Colosseum is amazing

and it weaves together not only structural engineering,

but mechanical water engineering, theatrics,

everything that you can think

of to make this production happen.

There's a lot going on here.

- [Narrator] In 80 CE, the Flavian amphitheater destined

to become known as the Colosseum

stands ready for its grand debut.

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- People have always been drawn to the Colosseum,

not just because it is an architectural masterpiece,

but because of what happens inside.

- The inaugural games are a dazzling display

of Roman power and ingenuity.

- Chariot races, wild beast spectacles,

gladiatorial combats, all sorts of things

going on for a hundred days, portraying the glory

of the Emperor Titus and his family

and the empire as a whole.

- This was an extraordinary spectacle

of slaughter and battle.

Thousands of animals were involved.

Thousands of people in these scenes of conflict

enslaved as well as criminals,

as well as professional fighter.

- [Narrator] Gladiatorial combat the highlight of the games

pit skilled warriors against each other

in tests of strength and strategy.

- The Roman Empire was an empire made through conquest,

so there was a lot of culture around the strength of arms.

So it's not surprising that for their own entertainment

it was focused on the same thing.

- You could become a gladiator if you were a free person,

but most of them were slaves.

But they could work their way up

if they were good gladiators,

and then they'd end up gaining a lot of riches

so that they'd be able to buy themselves out of slavery

and become real celebrities. (upbeat music)

- [Narrator] These battles though brutal,

a carefully choreographed performances

that captivate the audience.

- For your average Roman.

Entering the Colosseum was like an escape into grandeur

where they would witness magnificent blood

thirsty entertainment.

- The number of gladiators who died

is not as high as was traditionally thought,

but still death was a real possibility.

- [Narrator] But how much of this spectacle

has been embellished by the passage of time?

- Can't always trust the historical sources

a hundred percent, but it does seem

that these games were particularly spectacular.

There were amphitheaters putting on games

all around the Roman Empire,

but this one at the center of the empire,

the embodiment of the empire was the greatest of them all.

- [Narrator] But where did the need

for these grand violent spectacles

and a grand stadium to hold them originate?

- The Colosseum when it was built came

after a period of tremendous instability.

This is the period of transition

from the earlier 500 years of Republican government

moving into what becomes increasingly an imperial state.

- The late Roman Republic was a time of great turmoil

with the powerful fighting amongst themselves.

It ended with Augustus claiming basically the throne.

Augustus brings a time of real stability

to the Roman Empire, but it doesn't last long

because his relatives who succeeded him

were not always all that stable.

Nero's rule was particularly disastrous for Rome.

- Nero was a man who didn't care about governance,

who was interested in establishing his power,

but was ruthless in his pursuit of it.

- Nero as an emperor was very self-indulgent.

The entire empire was there to serve him,

and he sets the tone for all

of the other major families of Rome.

- [Narrator] The Flavian dynasty and its first emperor,

Vespasian, comes to power in 69 CE,

after a period of civil war and unrest.

- When Nero was overthrown.

We have the year of the four emperors,

Galba, Otho, Vitellius, and Vespasian.

Vespasian was an older man.

He was an experienced general and a successful general,

which garnered great respect from the Roman elite

and especially from the Roman armies.

He brought sanity to the rule of Rome.

- After a period of tremendous disorder

when people couldn't even feed themselves very well.

When there was rapidly increasing violence.

To have signs of stability

was incredibly important and meaningful.

So here was an opportunity for Vespasian

to establish himself as the single most powerful

and unmatchable ruler of Rome,

the Roman Empire, but also the Roman people.

- Part of the emperor's control over the empire

had to do with bread and circuses,

feed the people, and also games to entertain them.

- A common person who's there at the Gladiatorial games

might not have the best of lives, but at the same time,

they're not risking life for limb.

And so theory is that you can produce morale

if you can show somebody's worse off.

- Rome was a crowded place,

not a particularly pleasant place.

Lots of potential for uprisings, rebellions, riots.

- Keep the people happy, give them enjoyment,

that lets them not think about their daily lives.

And then we repeat this, right?

We go to our own sports arenas and see top athletes compete,

root for our special teams, root against the other teams,

or just go and enjoy a really good game.

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- You wanted a venue like the Colosseum,

a big amphitheater where thousands,

tens of thousands of people could come to be entertained

by gladiatorial games or battle reenactments,

or chariot races or whatever it might be.

- [Narrator] Vespasian identifies Nero's,

extravagant palace complex, the Domus Aurea,

as the chosen site for his massive engineering project.

- When the great fire of Rome hit in 64 AD,

it wiped out a large part of the city

and Nero's reputation took a big hit as a result.

There are rumors that he had sent his servants

to set the fire because after the fire was over,

Nero thought it a good idea to build a golden house

on the burned out remains of Rome.

- Nero's massive palace complex symbolized

his extravagance in the eyes of Roman people.

They saw this as a monument to imperial self-indulgence.

- It was a heartless exploitation

of what had devastated the people as a whole.

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- [Narrator] The space's decision to construct the Colosseum

on the site of Nero's palace is a calculated move.

- Vespasian was starting a new dynasty and he had to show

himself superior to the previous dynasty.

If he could exploit what was disreputable in Nero's rule

and do something for the people, something glorious,

spectacular, then that would give his dynasty

the position he wanted for it.

- So here we have this palace co-opted

to build a public space, a public place of gathering,

that belongs to the Roman people.

- Everybody's invited, everybody can come.

The emperor's there, the leaders are there.

They're in their own boxes.

Just like we have box seats now,

where people with more means don't sit with the rest of us.

So in some ways it is reinforcing the social strata

within the Roman Empire, but for the common person

who's in there watching the games,

they see themselves as doing something that even the emperor

is doing and there's not much in their lives

that they get to do, especially entertainment.

That is entertainment for the emperor.

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- [Narrator] Carrying out Ian's ambitious plan

would require a solid foundation to bear the immense weight

of the proposed structure.

- It's really important that we have really firm foundations

so our buildings don't settle and move.

A great example of a building that had a terrible foundation

is the leaning tower pizza.

We had this building where the foundations weren't adequate.

The soils have flowed under the building

and now the building leans significantly.

- [Narrator] But for this new amphitheater,

there are significant challenges to be met.

The Vespasian chosen site at the center

of Nero sprawling Domus Aurea is a marshy area

containing a 20,000 square meter artificial lake.

- So you picked a site that is on a lake basically,

so you have to get rid of that lake first

before you can even build the structure.

That means dewatering that lake, looking at that soil,

that might not be great for building on,

and increasing its ability to bear a giant structure on it.

It's a big project.

- [Narrator] Once they've drained the artificial lake,

they excavate the site 12 meters deep down to solid ground.

- When we are talking about building a structure

like the Colosseum on a drained lake,

we have a lot of issues with the soils,

a lot of clay, a lot of sand.

We're gonna have to dig down through those silty clay layers

to something more stable.

We're moving 220,000 metric tons of material.

This is something we can easily do nowadays,

but in that period it really is mind boggling

to think about it being done by manual labor.

- [Narrator] They then construct a foundation

over 12 meters thick consisting

of multiple layers of concrete.

- Concrete is an amazing material.

You have this material that when wet is flowable,

so you create a mold to pour that concrete into,

and then it sets up reasonably quickly into something

really strong and really durable.

- This is really a great example.

One of the first real engineered

is when we're really starting to produce real concretes

and really have some understanding of how they work.

- [Narrator] The Colosseum's concrete foundation is credited

as a key factor in its remarkable longevity,

providing a solid base for the tons

of other materials placed on top of it,

including approximately 99,000 cubic meters

of travertine stone, 300 tons of iron clamps,

and a million bricks.

The piece is still standing today,

offer critical insights into its construction techniques.

- We can see evidence of the backbone of the structure,

these massive blocks that served

as robust load-bearing pillars.

These blocks are punctured by numerous holes,

remnants of iron clamps and dolls

that once held the stones together.

Over the centuries, these metal fixtures were removed

and repurposed, but they still leave behind their marks.

- [Narrator] The walls and stairs are crafted

from a combination of bricks and tough,

a softer volcanic rock providing

both strength and flexibility.

- The Colosseum has a really interesting cross section.

It's structurally really capable.

You can easily identify the series of arches and vaults,

and they use the materials in a configuration

that makes good sense to carry the weight of the people

who would be visiting the Colosseum

and the materials themselves.

- [Narrator] What techniques and tools

did the ancient Romans have to erect these impressive walls,

arches and vaults on a structure

that reached a height of 48 meters at its highest point,

- Many ancient civilizations started

to develop technology around mechanics.

They understood incline planes,

so ramps and why they help move large objects.

But when you're moving a very large block

up an immense distance, you have to have a huge ramp

for it to be an effective incline plane.

And that means that it's really hard to build vertically.

To build vertically, we need a different technology,

and that's where cranes come in.

Cranes allow us to lift objects vertically

instead of pushing them up incline planes,

- [Narrator] But uncovering conclusive evidence

about the ancient Romans building tools is challenging.

- Because Roman cranes were made from wood,

a perishable material.

Complete remains are virtually non-existent.

Only small components like pulleys, cable pieces,

and iron reinforcements have been found

in the archeological exploration.

- We have really good historical records

from the Roman period, and so even though

we don't necessarily have all the physical tools

and we still have an idea of how things are done,

either through writings or drawings,

that allows us to try to piece together

how some of these structures came together.

- [Narrator] The earliest crane technology

can be traced back to the ancient Greeks

in the sixth century, BCE,

whose machines revolutionized construction techniques.

- The technology of cranes really comes down to pulleys.

And pullies are really neat.

So if I take one single pulley and I put a load on one side,

if I have a hundred pounds here,

I'll have to pull with a hundred pounds here to lift up.

But what I can do is I can put a pulley at the top

and a pulley at the bottom.

What happens is each of the ropes that loop

around the pulley start to carry some of the load.

All of a sudden, I need much less force

pulling down to lift a very huge object.

So no longer do we have to have the 100 pounds

lifting 100 pounds, I can have 400 pounds of people,

pulling on a rope lifting a six ton block.

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- [Narrator] But even the most advanced lifting techniques

used by the ancient Romans would require

significant human power.

- Slave labor was a reality throughout the ancient world,

and certainly the Colosseum is a perfect example of that,

and it was drawn from all parts of the empire.

But in particular, we think from the enslaved populations

that were taken out of Jerusalem

following its conquest in 70 CE,

and we think it's upwards of 60,000, to a 100,000 people

from Jerusalem were brought.

- [Narrator] Upon its completion,

under Vespasian's son Titus,

the Colosseum would be defined by its gladiatorial contests

and animal hunts all taking place on a floor

made up of a wooden platform covered in sand.

But those early years would feature another spectacle,

one that would transform that floor

turning the Colosseum into something entirely unexpected,

a stage for grand naval battles.

- One of the most impressive spectacles

that the Romans loved were the Naumachiae.

Often they would reenact a famous historical

naval battle and the people loved them.

- [Narrator] These elaborate theatrical productions

typically involved large artificial basins or lakes

where ships manned by prisoners of war

or condemned criminals would engage in dramatic sea battles.

- And these naval battles actually became one of the new

innovations of spectacle during the time of Julius Caesar

to celebrate his own victories.

Over time, however, these were getting more dramatic.

They were getting more elaborate.

They had to keep innovating in order

to keep the attention of the populace.

- There are historical references to naval battles

taking place in the Colosseum,

but we're not absolutely sure they really did.

- [Narrator] Despite ancient writings by Cassius Dio

and poet Martial to back it up,

some historians remain skeptical.

- There's a lot written about it historically,

which leads you to believe

there's gotta be some truth about it.

But in terms of actually nailing down the science

of how it was done, there's still some debate around that.

- [Narrator] These spectacles are so grandiose

that they almost seem impossible.

- If you were just a standard person who was there,

the idea that it could be flooded to have naval battles,

that's something that couldn't easily be expected.

It almost feels like magic.

- [Narrator] How could the ancient Romans

have achieved such watery spectacle within the Colosseum,

with the technology available to them at the time?

- It totally changes the landscape

of how you're gonna design this,

and you have to start weaving in the mechanical systems

to deliver that water, manage that water,

take that water away.

- One of the things about water

is it's very difficult to pump

and it takes an immense amount of energy to pump water.

So we need a different technology

and that's where aqueducts come in.

So what an aqueduct is, it's a bridge system

that brings water from higher elevations into another area

that could use the natural gravity

and the flow of water to get water

to go where they wanted it to.

- The Roman Empire is filled with aqueduct.

It's one of the things you see that still exists today.

The Claudian aqueduct alone could discharge

up to 2200 liters per second.

One of the theories is that they were able to basically

divert some of the water from the aqueducts

to the Colosseum, which would've filled it very rapidly.

- [Narrator] Another theory posits that the Colosseum

had a sophisticated system

of underground chambers and sluice gates.

- Basically, a sluice gate is kind of like a big valve.

It basically is a door that prevents water from flowing,

and when we open that door, the water can flow in quickly.

So sluice gates are really a great way

in combination with reservoirs

to fill the Colosseum with water very quickly.

- The Colosseum's original underground area

is altered beyond recognition, making it almost impossible

to reconstruct exactly how flooding would've worked,

but could the answers be found within this massive

renovation itself.

- [Narrator] Beneath the floor of the Colosseum today

lies a complex labyrinth of underground tunnels.

After decades of neglect,

it has finally been unearthed by archeologists.

- How did the Romans build such a complex

underground structure?

And what was it for?

- [Narrator] In 83 CE, Titus's successor, Emperor Domitian,

commissions builder heter to build an intricate network

of tunnels and lifts beneath the amphitheater,

called a hypogeum.

- The word hypogeum taken from Greek means under the earth,

so the term could have included anything

that was built under the floor of the Colosseum.

- [Narrator] Through painstaking analysis,

archeologists are gradually uncovering

how herter is ingenious engineering revolutionized

the spectacles at the Colosseum.

- The building of the hypogeum a few years

after the opening ceremonies marks a move away

from naval battles to a focus much more

on gladiatorial combat and on human and animal combat.

They built in lifts and elevators that will allow

for surprise moments in the spectacles,

in the form of animals and gladiators,

being able to move up quickly onto the floor

of the Colosseum to join in a combat.

- There's this whole city of activity

that happens under the stage,

and the whole system worked together

between a series of pulley and lifts and ramps

and all sorts of different elements that allowed

sort of this surprise entertainment to occur.

- It's really quite impressive when you have, you know,

six people standing on a platform

all of a sudden come up out of the ground.

And it would be astonishing to people of the time.

- In 404 CE, the gladiator games were discontinued

and the Colosseum fell into disrepair.

- The Roman Empire falls over time and the Colosseum,

along with the empire, will find its purpose diminished.

It will be neglected in the overrun.

It will eventually be converted into a Christian space

by the Catholic church as a way of showing

the conquest of the Christian tradition.

And over time we'll see it repurposed again and again.

But to this day, it still stands,

and I think we have to keep in mind those long histories

to really understand its legacy.

- [Narrator] Despite the passage of time,

the Colosseum continues to evoke the spirit

of the Roman Empire in both grandeur

and the darker aspect of its history.

And while it's difficult to contend

with the engineering might of the ancient Romans,

another ancient structure rivals even the Colosseum

in its sheer scale and ambition, the Great Wall of China,

winds majestically across mountains, deserts, and planes,

symbolizing the strength and visionary ambition

of a civilization determined to safeguard its heritage.

- Stretching over 21,000 kilometers, the Great wall of China

is the longest manmade structure in the world.

- It remains a powerful symbol of China's imperial past,

but it's also a powerful symbol of the history of China

as part of a diverse, multi-faith, multi-ethnic world

in which they had to engage.

- [Narrator] Contending with a wide range

of challenging terrains, the wall's architectural styles

and construction techniques are tailored

to the various landscapes it traverses.

- You're confronted with so many different things

that you can't anticipate, but you have to react

to what you encounter and work with

what you've got in a remote area building this massive wall.

- The construction methods of the wall

evolved massively over time.

So earlier sections reveal rammed earth, wood,

and stone used in construction.

Later sections of the wall reveal much more sophisticated

construction methods with bricks and cuts stone blocks.

- Archeologically speaking,

there's a lot of history and information

that is sort of entombed within the construction

of this wall, and it can tell us a lot about

the history of China over the period of construction.

- [Narrator] But even after centuries of study,

the Great Wall continues to evade full comprehension.

- There are some parts that are extremely well preserved

and there's been some reconstruction,

but there are also parts of the wall

that are just crumbling and dilapidated.

So you've got different segments that look different

depending on sort of what state

of disrepair they might be in.

- The estimate as much as 30% of it has disappeared,

which means we're really having to rely

on the remaining 70% to unlock its history.

And that poses challenges

because we don't have written documents in many cases,

this is an enormous wall,

but all the sections are different,

and clearly they were designed to serve different purposes.

So what were they intended to do?

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- [Narrator] Propped up along the mountain ridge,

one of the most remote stretches of the Great Wall of China

offers a unique window into the secrets of its past.

- This is one of the most remote and challenging sections

of the Great Wall, just given the natural landscape,

and so it's essentially been untouched for centuries.

- [Narrator] Recent restoration efforts have ignited

new interest in this previously neglected section.

Stone tablets unearthed on the Jiankou section

bear Inscriptions that once decoded offer critical insights.

- Inscriptions show that several beacon towers and the walls

connecting them were constructed on vastly

different timelines.

This means this section took more than four decades

to build, suggesting a phased approach,

adapting to changing needs and challenges.

- Anytime you uncover a historical record,

like actual written text or some sort of written format

is really exciting because then you can start to validate

what you're seeing and what you're finding

with that historical record or what's been written.

- [Narrator] The concept of border walls in China

dates back to the seventh century BCE,

during the tumultuous Warring states period.

- We have many different power structures,

some of which are competing with one another,

some of which are cooperating with one another,

but they're also having to engage

with other cultures nearby.

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- [Narrator] During this time, the individual states

all construct their own walls.

After unifying China in 221 BCE, Emperor Qin Shi Huang

orchestrates a massive project to connect and expand

the existing walls into a more cohesive structure.

- This marked the birth of the Great Wall

as a unified concept.

- [Narrator] In the centuries that follow,

successive dynasties continue to strengthen

and expand the wall, gradually transforming it

into a more sophisticated defense system.

But it was the Ming Dynasty founded in the 14th century,

that would establish the monumental edifice

we recognize today.

- The Ming Dynasty, of course, is very well known

to many of us through its cultural legacy

in the form of a beautiful ceramics and so forth.

But it was at the time also a new dynasty

that was trying to distinguish itself

from previous dynasties by celebrating its role

as an administrating power.

It was very important to them to establish the rule

in the eyes of the people they were governing as stable,

as concerned about peace. (upbeat music)

- [Narrator] The Ming Emperors take wall building

to new heights quite literally,

but who are they so determined to keep out?

With an average height of eight meters tall,

the Great Wall is often hailed as an impenetrable barrier,

a monument to ancient engineering

that kept invaders at bay for centuries.

- But was the wall really impenetrable?

- [Narrator] According to legend,

the Great Wall was breached multiple times

throughout history, including 14 times,

by the Mongolian army in the early 16th century.

- We think of walls historically,

we tend to think of them as defensive

or protective measures only,

but walls are not simply to keep people out,

they're to regulate your relations with others,

some who are hostile,

but some who are simply their neighbors,

who they have to also have communication with,

trade with, and so forth.

So it's also actually a border,

a boundary that is like a gateway.

- One of the things with large structures like walls

is it's not only a barrier to our enemies,

but a barrier to ourselves.

So you always want to have some type of pass through

through your structure so that you can get out of it.

- [Narrator] Besides the hundreds of official passes

through the wall, recent discoveries unveil ruins

of over 130 hidden doors within the Great Wall,

further challenging the notion of its absolute security.

- Basically built arch tunnels through the structure,

so that would be self-supporting

and they'd be able to make an egress out

the other side of the wall. (bright upbeat music)

- [Narrator] Some of the most intriguing passages

have exits designed with a careful camouflage.

- The exits facing the enemy are constructed with brick

making them near impossible to detect from the outside.

However, from the inside, they're hollowed out,

allowing the defenders to launch surprise

sudden attacks on the enemy.

- [Narrator] These discoveries revealed that the Great Wall

was not a completely closed off structure,

but one that could be covertly and strategically opened.

- Although previous dynasties had expansionist policies,

the Ming Dynasty adopted a defensive one.

- [Narrator] They concentrated on fortifying their borders

and consolidating control over their existing territory.

This defensive focus,

particularly against the northern threats,

led to significant investments in the Great Wall,

transforming it into a complex multi-layered

defense installation.

- It was a big building dynasty,

and so the wall in this time became very important

as a way of broadcasting its interest

and being a protector and a defender of the population,

not as an expansionist power.

- [Narrator] At its peak, the Great Wall boasted

approximately 25,000 towers along its length.

Typically standing 10 meters tall, we find these towers

primarily on elevated points, hilltops, ridges,

and mountain peaks, allowing for a 360 degree view

on the surrounding terrain. (upbeat music)

These towers serve multiple purposes

as defensive structures and observation posts,

but they also function as signal stations.

- These towers were strategically placed,

enabling rapid communication across the length of the wall.

(upbeat music)

- [Narrator] Using smoke signals by day

and fire beacons by night, guards can quickly relay messages

from station to station.

- Signal towers were very important to maintaining

local power from a great distance.

Every five kilometers, there was another signal tower.

Travel on foot would take a long time,

but to communicate by smoke signals means

that they could quickly learn

if there was some serious issue on the border and mobilize.

- [Narrator] These towers typically have three stories.

While the top floor is used for observation and signaling,

the first two floors serve as living quarters for soldiers.

- The soldiers who were sent to the wall

came from all sorts of other parts of China.

They're stationed on parts of the wall

for long periods of time.

So what is that life like?

(upbeat music)

- [Narrator] At the top of one Beacon Tower,

archeologists found a hearth,

likely built to help soldiers endure harsh winters

and to use for cooking. (upbeat music)

This discovery offers a window into the daily lives

of the soldiers who called these watchtowers home.

(upbeat music)

- The lives of these soldiers

were defined by vigilance and endurance.

They were isolated, removed from family,

so they were lonely.

They were also on high alert,

constantly aware of a potential attack.

- So you're supposed to be in a constant state of vigilance,

but what you end up getting is an awful

lot of operational fatigue.

It's the same thing day in and day out.

You're expected to be ready for the one time

something might happen in what a couple years.

- [Narrator] The construction of these towers on elevated,

often remote locations presented unique challenges

to ancient engineers and builders.

- Across the length of the Great Wall

there's 25,000 of these signal towers,

and they're built at strategic locations,

really difficult terrain.

We're talking on mountain ridges on hills,

and just thinking about building something

in this remote location with not a lot of materials,

not a lot of access, that's a huge undertaking.

- [Narrator] Throughout its vast history.

The Wall's construction is estimated to have required

an astonishing 100 million tons of stone, bricks and mud.

But the secret to the longevity of the Great Wall

may be in the stuff that holds it all together.

- The use of mortar in the Great Wall of China

is really what helped preserve it for millennia.

So mortar not only acts as part of the strength

of the structure, but it acts as a seal to keep the elements

out of the actual structure itself.

So if I don't have mortar, what happens is water

gets in and it freezes and it expands,

and it very quickly breaks down large structures.

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- [Narrator] Centuries before modern science

unraveled its unique properties.

Ancient Chinese builders harness the power

of a remarkable albeit unassuming material.

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- The Chinese were using a special mortar

that they had invented.

It was using sticky rice as a main constituent

to really make this mortar quite tough.

- Sticky rice has sugars in it.

Sugars are a lot like modern polymers,

and we can get what we call polysaccharides,

which are even longer sugar trains

much more similar to polymers again,

which is what's in sticky rice.

So you take a mortar material,

which isn't particularly good, it's strong enough,

but it doesn't weather well.

And then you take something like the polysaccharides

in sticky rice, which aren't gonna be strong enough

to support the wall, but seal really well.

And all of a sudden when you mix these two materials,

you have an engineered material

that is now able to provide all the necessary conditions

to act as an excellent mortar.

- [Narrator] Scientists in China studying this mortar

found it to be the world's first example

of composite mortar,

combining both organic and inorganic materials.

- This mortar is quite a dense mortar that prohibited

this sort of cracking or failure of it,

which allowed it to stay intact and prevent

vegetation growth from happening.

- It's a really interesting and distinct

cultural dimension of the wall.

It shows an adaptation to local resources

that it sets it apart from any other monumental building

that you'd see for example, in Western Europe.

- [Narrator] The sheer scale of the Great Walls construction

is almost unimaginable.

Chinese engineers and builders coordinated

this gargantuan task using methods

that were greatly dependent on the terrain

and available resources.

- On flatter land, they would've used horses

and oxen and in drier climates, even camels.

But ultimately, this great wall was built with human hands.

- We didn't have, you know, the excavators,

the earth moving equipment, the trucks, the cranes,

that are in modern societies.

So everything is done by human power.

The Great Wall of China is a project that literally

lasted centuries, and this takes millions and millions

and millions of man hours to construct.

- Many of them would've been enslaved

or prisoners or paid helpers.

But the bottom line is that this kind of project

at the end of the day relied on human labor

that would've involved the transportation of materials

in many cases from very, very long distances.

- [Narrator] While the Great Walls stands

as a testament to human ingenuity,

it also bears a darker legacy, one that has earned it

the grim title of the world's longest graveyard.

- The human cost of building

the Great Wall of China was staggering.

As many as 400,000 people may have died

during its construction.

Many of these workers were convicts

or peasants forced into labor.

They faced brutal conditions, insufficient food,

treacherous terrain, and harsh weather.

- [Narrator] The huge numbers of deaths led to the rumors

of the bones of dead workers being used

in the construction of the wall.

- While there would be many deaths

during the construction of the Great Wall,

we don't actually find evidence that supports,

you know, bodies were thrown into the wall

during construction or buried or entombed in the wall

as it was being built.

And I think it's just part of oral history or rumors

being spread that gets translated over time.

- In a lot of sites like this,

there's a lot of wonder surrounding it,

and this mythology turns into folk stories and legends.

So from an archeological perspective

is trying to decipher fact from fiction,

and we can do that through the archeological record.

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- [Narrator] As researchers continue their attempts

at unraveling the Wall's mysteries,

it becomes clear that the Great Wall of China stands today

as far more than the remnants of a military barrier.

And while the Great Wall serves as a symbol

of defensive ingenuity spanning millennia,

another formidable structure in medieval Europe

tells a different story of power

and protection against its adversaries.

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In Northern Poland, looms one of the most formidable

medieval fortresses in the world.

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- This is the large brick castle by land area.

Some 52 acres containing an estimated 30 million bricks.

- It's surrounded by moats and defensive walls.

It is a site to behold.

- [Narrator] Once the seat of power for the order.

This Grand Castle was designed as an impenetrable bulwark

against external threats.

- Why was building on such a massive scale

so important to important to the Teutonic Knights?

- Was it a practical measure

because of their growing numbers,

or did it represent something to do

with their grand ambitions?

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- The Teutonic Knights were a formidable Catholic

organization that emerged in the late 12th century

during the Crusades.

- The Teutonic Knights represent a new type

of religious order, half monk and half knights.

Knights that take monastic vows.

- The Teutonic Knights were one of the many military orders

which are formed amongst the European nobility

to go and rescue Jerusalem

from the Muslim rulers of the time.

- In the 13th century, the order begins to expand

and take on a new purpose

with the so-called Northern Crusades.

At that point in time, the Baltic region of Europe

was still largely pagan, and the Teutonic Knights

took it upon themselves to change that.

It became the basis for them to set up

the first monastic state for the order.

- They essentially introduced a theocracy in Prussia.

A theocracy is a government in which church

and state are collapsed.

So the Teutonic Knights themselves were the rulers

as a religious order of the state,

which they carved out for themselves.

And this is a society that they formed

and that was centered at Malbork Castle

- [Narrator] Construction of Malbork Castle

is initiated by the order around 1274,

following their success during the Prussian Crusade.

- Building a castle on such a large scale was symbolic.

It was letting the world know

that this was a serious organization,

this was an important organization,

and they were making their mark on the globe.

- Castles are often built over a long period of time.

They'll have one structure

and then they'll keep adapting them and innovating

and adding to them as their needs change

and as they face new challenges over time.

So Malbork Castle is a good example of that.

- The High Castle, the oldest park,

served as the monastic center of the complex,

embodying the orders of religious foundations.

- [Narrator] Malbork Castle was more

than just a military stronghold.

It was a city unto itself,

housing hundreds of knights, servants, and craftsmen.

- In 1309, the Teutonic order moves their headquarters

into Malbork Castle.

- [Narrator] The arrival of the order's Grand Master

necessitates the construction of an entirely new section

of the fortress.

- The Middle Castle was added in 1309,

and was built to accommodate

the increasing number of knights.

And the grandmas court featuring grant halls

for ceremonies and receptions.

- As their power territorial control expands,

their numbers begin to swell.

At their height it's estimated that Malbork Castle

was home to 3000 knights.

- When we look at the various military orders,

often they were traveling to other countries,

and one of the things that kept a military order

together was the idea of having a home.

So in building this home base for the Teutonic Knights,

it actually helps knit that brotherhood stronger together.

- The low castle, also known as the Outer Castle,

was the final edition.

It was constructed during the late 14th

and early 15th centuries and served economic

and defensive purposes.

- The growing complexity of Malbork Castle

represented the growing complexity of the Teutonic Order.

No longer were they just knights, now they were diplomats,

now they were administrators,

now they were religious leaders.

- [Narrator] But the grand scale and strong defenses

of Malbork are necessitated by the formidable enemies

of the Teutonic Knights.

- Malbork Castle is a physical symbol of their strength.

It looks strong and imposing.

It looks like it's going to last forever.

And these are all the features that the knights

wanted their enemies to be afraid of.

We are strong, we are impenetrable.

We will always last. You should fear us.

- [Narrator] In 1410, the Teutonic Order finds itself

at a critical juncture as the Battle of Grunwald

marks a dramatic turning point in medieval history.

- This was a monumental clash

between the Polish Lithuanian Alliance,

and the Teutonic Knights.

- [Narrator] The alliance was formed by the kingdom

of Poland and the Grand Duchy of Lithuania in 1409.

After a series of territorial disputes

with the Teutonic Order led to a declaration of war,

- The alliance doesn't just wanna win on the battlefield,

they wanna dismantle the entire Teutonic Order.

To do that, they have to take the castle.

Some 39,000 soldiers at the Polish Lithuanian Alliance

gather outside the castle.

Just 27,000 knights remain inside the defendant.

- [Narrator] The alliance goes on to claim

a decisive victory in the battle itself.

With most of the Teutonic leadership killed

or taken prisoner, despite the defeat on the battlefield,

the Teutonic Knights are able to keep Malbork Castle.

But what secret lay within this fortress,

allowing the order to defend

against such a formidable force.

- The castle's design incorporated multiple layers

of defense, and each one would've been harder

to overcome than the last.

- If you have a simple castle with a single exterior wall,

once that wall is breached, you're done.

So castles need multiple technologies to prevent invaders

from capturing them very quickly.

So once the first wall gets breached,

you can move back behind another wall,

and then when that gets breached,

you can move again behind another wall.

- [Narrator] These were further reinforced

by both wet and dry moats,

adding extra depth to the castle's defenses.

- Basically, your attackers actually have to build

some kind of bridge structure to attack the wall,

and all the time they're constructing

or moving that structure into place,

you're free to attack from the castle walls.

- [Narrator] Towers serve jewel purposes as watch towers

and strongholds, allowing defenders to spot

approaching enemies from afar and providing strong points

of resistance during an attack.

The fortified gates are particularly impressive,

featuring a combination of drawbridges,

portcullises, and ironclad doors.

This multi-layered approach to gate defense makes breaching

the castle's entrance an extremely daunting task.

While the visible fortifications are impressive,

medieval castles often held secrets

beneath their imposing exteriors.

Legends persist of a network

of hidden tunnels beneath the castle.

- These underground tunnels were fairly common

in these types of structures.

Not only would these tunnels be used to get people

in and out, but they could be used for things

like supplies, food, weapons, ammunition.

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- A story has emerged of a terrified pilgrim

who seeks to escape during the siege.

And on his exit, he comes across a line of ghostly knights

who are allegedly headless.

- He's already gonna be fearful

because of the whole warfare and siege

that's going on and needing to make an escape,

you're in fight or flight mode.

So if he is afraid and he hears things,

he's gonna start imagining what could have made that sound.

- The terrified pilgrim flees, and allegedly,

the knights close off the tunnel keeping it hidden

and underground ever since.

- Ghost stories are very common in a lot of castles

because of their secret tunnels and underground spaces.

These were places of cultic worship.

These were places where you would hide

away from persecution.

These were also places where spirits were believed

to live in many different cultures.

- [Narrator] After over a century of power,

the Teutonic order never fully recovers

from the consequences of their defeat

at the Battle of Grunwald in 1410.

- The Teutonic Knights managed to successfully

defend Malbork Castle,

but the aura of their invincibility was badly shaken.

- [Narrator] The order would face a further setback in 1457,

during the 13 years war, fought once again against Poland.

In a dramatic twist, Teutonic mercenaries unpaid

and seeking compensation,

seize the castle and sell it to the Polish King.

This marks the end of Teutonic control over Malbork,

transforming it into a Polish royal residence

and a symbol of shifting power in the region.

The castle will go on to withstand further conflict

and later become part of Prussian territory.

Following the partition of Poland in 1772,

despite extensive damage during World War II,

Malbork Castle is meticulously restored

and now stands as a UNESCO World Heritage Site.

- Today, the castle serves as a bridge retreat,

past and present, offering insights into the ambitions,

ingenuity, and perhaps fears of those who built

and defended it centuries ago.

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- [Narrator] From the grandeur of Rome's Colosseum,

a testament to the might of ancient Rome

and its ability to entertain thousands,

to the great Wall of China destined to protect

an empire for millennia to Malbork Castle's, embodiment

of the grand ambitions of the Teutonic Knights.

These monumental works stand today as inspiring symbols

of the sheer scale of human ambition.

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