Original subtitles

(eerie dramatic music)

- [Narrator] Across the globe,

ancient architectural marvels stand as testaments

to human ingenuity.

However, within the stunning craftsmanship

of some of these structures, sinister whispers linger.

- People see something that is so majestic,

so perfect, so beautiful that they don't believe

it could have been created by human hands.

- [Narrator] In the Andean heights of Peru,

a colossal stone complex defies explanation.

Its seemingly impenetrable walls

stunning 16th-century conquerors.

- Why did the Spanish believe the Inca

called on dark forces to build their fortress?

- [Narrator] Deep in the arid landscape

of Rajasthan, India, the mesmerizing geometry

of an ancient stepwell plunges 13 stories into the earth.

Its intricate design seems almost otherworldly.

- King Chanda is trying to save his kingdom,

so he turns to the dark arts.

- [Narrator] Did a malevolent force perform

this architectural feat?

Rising above the streets of Paris,

the Gothic spires of a famed cathedral

have long echoed tales of demonic pacts.

- This is a bastion of the Christian faith.

Demons will want to play with it.

- [Narrator] What secrets lie hidden

in its elaborate designs?

Exploring these architectural wonders

uncovers the fine line between genius and the supernatural.

- It seemed like magic,

and it's not that much of a leap to go,

"The devil was involved."

- [Narrator] Could it be true?

Or do the real answers lie in forgotten human knowledge?

(dramatic music) (air whooshing)

(playful music)

High in the Andean mountains,

perched above the Peruvian city of Cusco,

lies Sacsayhuaman, a massive stone complex

that has baffled experts for centuries.

- The true purpose of this colossal structure

remains one of the greatest mysteries of Inca archeology.

Its layout hints at a level of sophistication

that we're only beginning to understand.

- [Narrator] With zigzagging walls

that stretch for hundreds of meters,

Sacsayhuaman's cryptic design speaks to a grand purpose.

- Commonly, it was believed that this was a fortress,

and that makes sense when you consider

its defensive walls and strategic location.

- [Narrator] But Sacsayhuaman's mysteries run deeper

than its imposing walls.

Below its foundation is a rumored labyrinth of tunnels,

potentially guarding ancient secrets

and a haunted passage to the underworld.

- Was this primarily a military fortress

or a religious center,

or something else entirely?

- [Narrator] When Spanish conquistadors arrived in Cusco

in the 16th century, they were bewildered

by the sight of Sacsayhuaman.

- It's hard to imagine what was going through the minds

of the Spanish conquistadors

the first time they set eyes on Sacsayhuaman.

- Well, the first sight of the fortress

must have been awe-inspiring,

it must have been intimidating.

- They had no frame of reference

for what they were seeing.

In some ways, the engineering met

or even exceeded what was possible back in Europe.

- They can't believe that it was constructed by the Incas

because they saw them as backward and uncivilized.

So in their mind,

they couldn't possibly build something

as magnificent and sophisticated as this fortress.

They swiftly attribute its construction

to demonic forces.

(eerie dramatic music)

- [Narrator] Nearly a century

before the conquistadors' arrival in Cusco,

Pachacuti Inca Yupanqui, the ninth Sapa Inca,

begins the transformation of the kingdom of Cusco

into the mighty Inca Empire,

the largest pre-Columbian empire in the Americas.

Pachacuti is a brilliant strategist.

During his reign, from 1438 to 1471 CE,

he expands Inca territory across western South America

through conquest and diplomacy,

and oversees massive construction projects,

including Machu Picchu and Sacsayhuaman,

marking the beginning of the Inca Empire's Golden Age.

Cusco serves as the capital of the Incan Empire

until the Spanish conquistadors arrive in the 16th century,

an event that would be the catalyst for a bloody battle.

- It's November 1533,

Francisco Pizarro and his conquistadors

have arrived in Cusco.

This moment marks the culmination

of a decade of Spanish aggression in the Americas.

In 1521, Hernan Cortes had conquered

the Aztec Empire for Spain.

Now, Francisco Pizarro seemed poised

to do the same to the Incas.

- [Narrator] The Spanish are initially welcomed in Cusco.

Earlier that year, Pizarro's forces

had captured and executed the Inca emperor, Atahualpa,

and installed the young Manco Inca as a puppet ruler.

- But things started to go bad shortly thereafter,

and tensions began to rise.

The Spanish began to strip the city

of all of its gold and silver.

They looted the sacred buildings of the city,

and all of this reached the breaking point.

In 1536, Manco Inca led a rebellion

against the Spanish conquistadors,

culminating in the siege of Cusco.

- [Narrator] Sacsayhuaman's role in the siege

is a crucial one.

Its position overlooking Cusco

makes it an ideal spot as the headquarters

for the 200,000 warriors Manco has assembled.

- For the Spanish, getting control of Sacsayhuaman

is suddenly now a strategic objective.

(dramatic music)

- [Narrator] In May of 1536,

a force of 50 cavalry

and 120 Spanish infantry stormed the complex.

A bloody battle ensues,

but the Spanish eventually succeed

in capturing Sacsayhuaman.

This victory serves as a pivotal moment

in their efforts to break the siege of Cusco.

- In the chaos that followed,

many Inca warriors threw themselves from the walls,

death being preferable to being captured by the Spanish.

So it's interesting to ask

what these events can tell us

about the intended use of Sacsayhuaman.

Was it actually intended to be a fortress,

or was it just being used as one out of necessity?

- New evidence suggests the structure

may have served a much more practical purpose.

- [Narrator] In 2008, archeologists made

a groundbreaking discovery,

suggesting a more complex role in Inca society,

one that may transcend its use as a simple fortress.

- They uncover the ruins of an ancient temple

near the site of Sacsayhuaman.

- [Narrator] The temple's interior

reveals a connection to the dead,

a series of intriguing structures

that point to sophisticated funerary practices.

- Within this temple,

they find 11 enclosures of varying sizes.

The configuration and contents of these chambers

strongly suggest its use for mummy burials.

- These mummification rituals were very important,

very significant in Inca culture.

Clearly, they had an understanding

that it was important to preserve the body

for passage to the afterlife.

- [Narrator] While the archeological evidence suggests

that the site's origins may stretch back

even further than the Incas,

it is believed that the Inca significantly expanded

and developed the structure.

The presence of this temple

and its secret funerary enclosures

may hint at its role in connecting the human realm

to that which lies beyond.

- Could other undiscovered structures in this area

help further expand our knowledge of this site?

Or does the truth lie somewhere

within the mysterious patterns of the walls?

- [Narrator] The design of Sacsayhuaman

seems to be heavily influenced

by Incan religious beliefs,

and their tether to other realms.

- Inca religion was intimately tied to cosmology,

with their belief system centering on celestial deities.

- [Narrator] During his reign in the 15th century,

Pachacuti elevates the sun god, Inti,

to supreme status, reshaping the state religion.

- When people can't explain what's happening around them,

or they see the forces of nature,

they often turn them into spiritual beings or entities.

And so within this mysticism,

we find that there are sun gods

repeated over and over and over again.

The sun was the giver of life.

It also marked the seasons.

In the Incan culture, that was Inti.

- [Narrator] It's been theorized that Sacsayhuaman

was dedicated to the worship of this sun god.

And many elements of its design hint

at its mystical connections.

- The walls form this very distinct zigzagging pattern.

This angular shape creates

a series of sharp turns and recesses.

- [Narrator] Some suggest the design resembles

the head of a puma,

a sacred animal in Inca mythology,

with the city of Cusco forming the body.

- They had a complex understanding of the cosmos.

They recognized three realms,

and each of them were tied with significant creatures.

The underworld was associated with the serpent,

the earthly realm with the puma,

and the heavens with the condor.

- [Narrator] These three realms

and the cryptic language of the stars above

often govern the ancient Inca rituals and sacred sites.

- Many ancient civilizations actually put spiritual values

and powers into the animals that were around them.

They've anthropomorphized the animals themselves

to place a spiritual lead within that realm.

- [Narrator] Sacsayhuaman's position as the puma's head

emphasizes its importance

in connecting the earthly and spiritual realms.

But perhaps even more intriguing

is the theory that its layout incorporates

sophisticated astronomical alignments,

potentially encoding ancient knowledge.

Researchers have identified astronomical values

in both the pattern of its zigzag walls

and in the angles of the wall stones themselves,

which could indicate the alignment of the moon,

Earth, and sun at a given time,

and help predict lunar and solar eclipses.

Similar patterns found at ancient sites worldwide

raise intriguing questions about a shared knowledge

spanning continents and millennia.

This discovery could revolutionize

our understanding of ancient civilizations' capabilities.

But would the Inca really have had

the engineering foresight

to build such a grand complex

in the shape of a puma's head,

or to build complex astronomical values

into its very walls?

- We often wonder how the ancients accomplished

what they did.

But they knew a lot more than we give them credit for.

- The Inca people were amazing

at developing technology.

They built incredible structures,

they domesticated llamas and alpacas and guinea pigs.

They had terraced agriculture.

They had water control.

This society was very, very innovative

from a technological point of view.

- [Narrator] While a conclusive answer

to its original purpose may continue to evade us,

the stones of Sacsayhuaman themselves

hold their own secrets,

hinting at a mastery of construction

that continues to challenge mortal comprehension.

- These walls are built with massive stones,

some of them weighing up to 200 tons.

- [Narrator] Believing that only demonic forces

could have built Sacsayhuaman's amazing walls,

the Spanish attempt to take down the entire structure,

but reportedly find that the biggest stones

are simply too heavy to move.

- If the heaviest stones were too large to take down,

how on Earth were they erected in the first place?

- [Narrator] Could this have been the work

of otherworldly forces?

- We don't know how they built these walls,

but it's reasonable to say

that they had a good understanding of physics,

and they perhaps harnessed the power of levers

to move these giant boulders.

- [Narrator] It's believed they used wooden rollers

and levers to facilitate the movement of heavy stones

over relatively flat terrain,

and may have constructed ramps and inclined planes

for transporting up steep slopes.

- Where there's a will, there's a way,

and they figured it out.

- [Narrator] It's possible that over 20,000 workers

were involved in building this colossal fortress,

likely including laborers

who carried out the Herculean task

of transporting the stones from nearby quarries,

as well as the workers who assembled the walls.

But how did the Inca achieve

the seemingly impossible precision

in the stonework we still see today?

(chisel clanging)

- The Inca were master stonemasons,

renowned for their remarkable ability

to construct monumental structures

that have stood the test of time.

The strength of their empire

is often credited to this talent.

- And they used multiple techniques

in order to shape not only these massive stones,

but also to create very polished,

finely-decorated stones.

So clearly this is signs

of a very sophisticated artisanal culture,

but also a culture in which art and engineering

went hand in hand.

- [Narrator] Many stones still bear the marks

of the tools used to shape them,

suggesting the use of bronze chisels and stone hammers

to achieve the desired shape and smoothness.

The cutting and setting of the blocks

were so exact that mortar was unnecessary.

- Mortar is an important piece

to the durability of a brick wall.

If you were to build a wall without mortar,

you would likely have some gaps.

- That's a bit problematic

because you're going to get water flowing down

in between the rocks.

If you get freezing periods,

it's going to cause ice to form,

and when ice forms, it creates pressure,

and causes rocks to be pushed apart,

and basically destroys your construction

through natural weathering processes.

- Mortar would close those gaps

and allow for a more airtight structure.

However, they didn't use mortar

and instead they just shaped everything so precisely

that mortar wasn't needed.

Dry stone masonry is a really incredible way

to construct buildings,

and we're constructing basically a stone

that fits like a puzzle piece

into a larger part of a building,

we're matching every stone to the stones around it.

- [Narrator] Some believe they used methods similar

to those used in the building of log cabins,

called scribing and coping.

- Scribing is the act of shaping those stones

to match the profile of something else.

And coping is a precise cut,

sort of a carving out of something.

- This is beneficial from so many points of view.

It creates a very stable structure,

but it also resists weathering.

If we're not getting water flowing down

between our rocks 'cause they're so tight together,

we have a much better chance

of it enduring long periods of time

and not failing due to normal weathering processes.

- And they are just perfectly fit with no mortar.

There is no gap between them.

You can't even put a piece of paper in between there.

That is incredible.

They either coped, or carved, or cut out,

or sanded, or rounded all of these rocks.

Each one of these is a labor of love.

- [Narrator] But the Inca engineers

weren't just concerned with aesthetics.

They built with an eye towards longevity.

- The Incan Empire is built high in the Andes,

and the Andes are a geologically active area.

This area has massive earthquakes.

It's not uncommon to have magnitude seven-plus earthquakes

in this area.

And to build structures

that have been able to endure thousands of years

in this environment is amazing.

Where we use dry masonry,

because the stones fit together and lock together,

they don't want to tumble apart in an earthquake.

- And so that interlock of all of these stones together

can resist quite a bit of horizontal pressure on that wall,

be it from wind, from an impact from something,

or from soil consistently pressing on it.

They also were thoughtful

about the configuration of these walls,

they're in a zigzag pattern.

Each shift through that zigzag

adds lateral stability into these walls as well.

It acts as a unit to resist all of those forces

that it might experience.

To recognize that the need for robustness

around lateral forces in these ancient times

is pretty awesome.

- [Narrator] But the mysteries of its construction

don't end at its unshakable walls.

- Legend speaks of vast underground networks

connecting the fortress to other important Inca sites.

Some even claim these tunnels

stretch all the way to Cusco's Coricancha,

the most sacred temple of the Inca Empire.

- [Narrator] These tunnels could have served

multiple purposes, from storage and shelter,

to escape routes and ritualistic spaces.

Legends persist of vast chambers filled with gold

and precious artifacts hidden away

from Spanish conquistadors,

though no such treasures

have been officially discovered.

And for those who dare attempt to find it,

grave danger awaits. (eerie dramatic music)

In the 1920s, following the rumored disappearance

of several tunnel explorers,

all entryways were shuttered to the public,

though many are still tempted to venture below today.

According to some local tales,

these cursed passages promise to kill anyone

who steps foot inside.

Could this be otherworldly forces at work

guarding a potential channel to the underworld?

- Tunnels and passages come up again and again

when we talk about ancient structures.

And a lot of this comes to the idea that,

you know, a tunnel is a passageway,

and it has a mystical significance to it

because you don't know what's on the other end.

And you can imagine that if you travel down this tunnel,

you will leave one realm and enter another.

- [Narrator] Could the Spanish have seen these tunnels

as the source of the demonic forces

they believed built Sacsayhuaman?

- It's interesting to reflect, as a modern person,

that descriptions of demons

creating the structure seems foreign,

it seems unreasonable to us.

But in fact, that would have been perfectly natural,

it would have been a rational interpretation

for someone like Pizarro.

- There's a tendency on the part of many conquerors

to see the people that they were conquering

as inferior and incapable,

and being bound by the powers of darkness.

- When we're faced with something

we don't know how it happened, how it was built,

or it just looks beyond normal abilities of man,

we put it into the supernatural.

we put it onto the side of the divine,

if it's something that matches with our religion.

But the primitives, the heathens,

they're the ones that are supporting

the negative side of the spirituality,

devils, demons, the underworld.

- Early modern people understood

that the devil was real, the devil was present,

that the devil's function

was to create chaos, havoc, destruction.

And so for someone like Pizarro,

encountering the Incas would have reminded him

of the ever-present reality of the demonic.

- So when we consider how the Spanish minimized

and underestimated the Inca,

it's worth asking ourselves

if we don't do the same thing sometimes

when we look at the accomplishments

of other ancient civilizations.

(dramatic music)

- [Narrator] Halfway across the world

lies another architectural enigma.

Like Sacsayhuaman, its geometry and impossible scale

whisper of origins beyond mortal comprehension.

India, a land of ancient wonders and rich cultural heritage,

boasts a remarkable array of architectural marvels

that have stood the test of time.

While iconic sites like the Taj Mahal

often steal the spotlight,

some of India's most tantalizing structures

continue to perplex historians today.

(dramatic music)

Hidden in the arid landscape of Rajasthan,

a descent into the depths awaits,

the Chand Baori stepwell.

- This is one of the largest and deepest stepwells in India,

reaching 13 storeys into the earth.

- [Narrator] Chand Baori is one of many stepwells in India

intended as a reservoir

during the region's dry spells.

But the intricate carvings and sculptures

that adorn its walls hint at a purpose

beyond mere water storage.

- It is not only beautiful,

but it must have required extraordinary precision

in its design and execution. (dramatic music)

- There's 3,500 steps in this.

You immediately recognize the geometry in this,

the thoughtful planning of these steps.

- These perfectly carved steps

form a mesmerizing geometric pattern.

- Why did they choose this specific geometric design?

Does it encode ancient knowledge or religious beliefs?

- [Narrator] The stepwell's precise construction

and vast scale raise intriguing questions

about the capabilities of its 9th century builders.

- How did these ancient architects achieve such precision

without modern surveying tools?

- It almost seems to defy the limits of ancient engineering.

- [Narrator] The hands that carved this subterranean stone

did so in worship of water. (water sloshing)

- So much of ancient cultures focuses around water.

For civilizations to thrive,

they need continuous access to it.

You have to have water.

- Nowadays, we have great access to water.

It's considered a basic necessity,

and it's always provided to us.

But back then, in places like India,

you had to collect the water

so there was enough for the community.

- In particular, in India, there are years

where you have monsoons

and you have immense amounts of water,

and then you'll have periods where there isn't a monsoon

and the water table will literally change by meters.

If we're not changing our technology

to address the changing water table,

our civilization is going to collapse.

So the most successful ancient civilizations

had ways to ensure continuous access to water.

And that's kind of where stepwells come in.

- The stepwells were a fascinating and ingenious structure

designed to serve as water reservoirs.

- The rainwater falls from the sky

and collects in the huge opening.

The rain then trickles down the steps

and collects in the bottom well.

The water then seeps through porous rock,

which replenishes the underground water table.

- Thirst and hunger are some of the strongest drives

that motivate people.

These are really basic drives,

and they're in some structures of the brain

that are the oldest ones conserved across evolution.

It's going to be a major driver

of how that society is formed

and how decisions are made.

And in this arid land,

it should be very easy to get a large community together

to build a stepwell

because it's something everybody can see that they,

their families, and their descendants are going to need.

- [Narrator] While ancient stepwells

were vital water sources in the arid regions of India,

their role transcended mere necessity.

- People gathered here not only to draw water,

but to socialize, exchange news,

and even for religious purposes.

- [Narrator] The intricately carved walls,

niches, and pavilions served as a backdrop

for storytelling and artistic performances,

transforming the stepwells into vibrant hubs

of daily life and cultural activity.

But the complexity of Chand Baori's construction,

its sheer scale and intricate design

has led to persistent questions about how it was built.

And, in the absence of clear answers,

local legends and folklore have flourished.

- When we think of a structure

that is essential to the survival of people,

that is also an extraordinary work of art in and of itself,

it was so beautiful that stories developed

around it being a supernatural creation.

- Legend has it that King Chanda

is trying to save his kingdom from drought.

- This king is driven to desperation.

He turned to the dark arts.

- [Narrator] In his darkest hour,

the king calls upon the help of a djinn,

a supernatural entity with malevolent powers.

The djinn agrees to build a stepwell.

But this offer of salvation

will come at a terrible price,

the surrender of the kingdom itself.

(dramatic music)

- Faced with an impossible choice,

the king accepts the terms,

prioritizing his people's survival over his own rule.

According to the tale, this supernatural being

constructs the entire stepwell in a single night.

- [Narrator] Then King Chanda experienced

a fortunate twist of fate.

- In recognizing the king's selfless act,

a saint intervenes and basically traps the djinn

in the bowels of the stepwell,

and the kingdom is restored.

- [Narrator] Imprisoned in the depths of this structure

for eternity, the legend of the djinn lingers

for centuries more.

Chand Baori's intricate design seems to defy

the limitations of its time,

leaving many to consider the haunting possibility

that such an entity may indeed be responsible.

However, modern archeology has revealed hints

about its true design.

While detailed records of Chand Baori's construction

have been lost to history,

careful examination of the structure and others like it

can offer some insights.

- We often think about structures

that are coming up from the ground,

that we're creating space above ground.

This is actually creating a space below grade.

And that's really interesting,

it's like inverting my whole world.

It's really cool.

- [Narrator] Excavation likely began

with digging the central well to reach water level.

This would have required precise surveying

to ensure the correct depth and width.

As the foundation was secured,

the greatest task still loomed overhead,

carving 3,500 narrow steps

up thirteen floors to ground level.

- This is a big structure where people are taking

not only a lot of time to carve those steps out,

but a lot of time to make sure that they're exactly

the size they need to be.

- [Narrator] The perfect symmetry of Chand Baori

implies a mastery of mathematics,

and potentially, a grasp of geometry

that surpasses the known knowledge of this era.

- When you're trying to build,

essentially, an inverted pyramid in the ground,

you need to know exactly what your pyramid

is going to look like before you start building it.

If you start changing angles,

you don't end up with a pyramid.

You end up with something that's very skewed

and would look aesthetically extremely unpleasing.

- [Narrator] The uniform size

and precise angles of the steps

suggest the use of standardized measurements

and possibly, templates.

- It takes a lot of precision in each step that you go down

to make sure you're going to end up where you need to be.

So you're literally measuring

within a few millimeters in each layer.

- Everything is meticulous,

the angles, the carving, the steps,

the pathways through.

There's just so much thought put into the circulation

of this system and how one would move through it.

- [Narrator] Could this seemingly impossible perfection

be a clue that the mysterious tale of the djinn is true?

Beyond practical function,

the design elements of Chand Baori

also play with its visitors' minds,

stirring a sense of awe, and perhaps a subtle unease.

- The stepwell is really interesting in its design

because of how it makes you feel when you look at it.

And that's because in nature,

yes, we have rough symmetry, right?

We've got two arms, two legs, two eyes,

but yet things aren't perfect in the natural world.

Here we see something that is balanced out and symmetric,

but it's all sharp corners, it's steps, it's lines.

The only place we normally see lines

are off on the horizon.

We don't see them in straight lines

in most any other places.

And because of it, it gives this sense of awe.

It's not something that is natural.

And therefore, we add extra meaning to the space,

to the place itself.

- [Narrator] Incorporated into the engineering design

of Chand Baori is an apparent secret of ancient wisdom,

one that suggests a strategy

for mitigating the desert's intense heat.

As you descend the steps of Chand Baori,

you would feel the temperature dropping,

defying the scorching heat above.

The cooling properties of the stepwell reveal themselves

when examining the layers of its design.

At first glance, the thick stone walls

appear only to serve as structural support,

but they are actually the first clue

to the stepwell's cooling mechanism.

The builders chose materials with high thermal mass,

creating a natural heat sink

that absorbs daytime heat,

and releases it slowly at night.

Further down, a noticeable chill permeates the air.

- The stepwell maintains a temperature of 5 to 6 degrees

cooler at its base than at its surface.

Was this an intentional design feature,

and if so, how did they calculate it?

- [Narrator] The ancient engineers seem to have tapped

into the Earth's natural cooling properties,

using the subterranean design

to access cooler underground layers.

The collected water itself isn't just for drinking.

It plays a crucial role

in a natural air conditioning system.

As water evaporates, it cools the surrounding air,

much like our own body's perspiration.

This natural cooling system is amplified

by the well's unique vertical structure,

which creates a chimney effect,

encouraging air circulation.

- By having that cooler water source flow down

and having wind that would blow on top,

it creates an interesting thermodynamic

where it will stay cooler down there.

- [Narrator] Warm air rises,

drawing cooler air from the water surface upwards,

resulting in a constant flow of breeze,

a certain shiver from the depths.

- Ancient engineers were able to create

a sophisticated climate control system,

transforming a water source into a cool oasis

in one of the world's hottest regions.

- In an arid, dry land,

cold water is not something most people get to experience.

Even the rains in the monsoons are warm,

so it adds another level of awe or mysticism

to the whole endeavor and the whole structure,

that they're experiencing something special here

that they cannot get anywhere else.

- [Narrator] While its design creates an oasis

in the desert heat,

its purpose extends beyond mere physical comfort,

as evidenced by a nearby temple

that hints at the site's deeper spiritual significance.

Just 100 meters west of Chand Baori

stands a temple dedicated to Harshat Mata,

the goddess of joy and happiness.

Built between the 7th and 7th centuries,

it's believed that this temple formed a complex

with Chand Baori.

Pilgrims would typically purify themselves

in the stepwell's waters

before entering the sacred temple ground.

- Water is sacred across many traditions,

and in Hindu, it has a particularly special role,

not only in ritual purification,

but water was part of the cosmos.

It was actually binding the earthly

and the celestial realms together.

So it was essential to their understanding,

not only of their lived experience,

their present life, but the afterlife.

- [Narrator] This connection also reveals

the stepwell's deep spiritual significance,

further emphasized by its intricate architectural details.

Many of the carvings adorning Chand Baori

depict Hindu deities and mythological scenes

and narrate sacred stories.

- These carvings transform the stepwell

into a three-dimensional religious text.

- [Narrator] Chand Baori was likely used

in conjunction with the nearby temple for centuries,

embodying the Hindu concept of finding divinity

in the most essential elements of life,

a tradition that has endured for over a millennium.

While the specifics of its construction remain elusive

and the legends of the djinn endure,

Chand Baori's ancient ingenuity

continues to stand the test of time.

- Today, India is turning back to its ancient wisdom

in order to tackle the modern water crisis.

- I think it is a testimony to the ingenuity

of the early designers of these stepwells

that they are now finding purpose again today.

In this period of climate change,

when we have increasing drought conditions locally,

stepwells are now being put back to work

because they are one of the most efficient means

of ensuring the survival of the local population.

- This revival of ancient wisdom

is testament to the fact

that these ancient stepwells

are not only relics of the past,

but potential answers for the future.

- [Narrator] As with Chand Baori,

the line between the mystical and the physical

blurs at a grand cathedral in Paris.

Legends whisper of gargoyles

that protect the cathedral from unseen threats,

and tales of diabolical pacts

that may have shaped its very doors.

Standing majestically in the heart of Paris,

Notre Dame Cathedral,

completed in the mid-13th century,

has captivated visitors for hundreds of years.

- It stands as one of the world's oldest

and most renowned Gothic cathedrals.

- Notre Dame has witnessed pivotal moments

in French history,

from the coronation of Napoleon Bonaparte,

to the beatification of Joan of Arc.

- [Narrator] The cathedral's impressive dimensions,

with towers reaching 69 meters into the sky,

speak to the ambition of its builders.

- This was a cathedral built through the financial

and artisanal contributions of the local population.

It was intended to be the largest,

the most sophisticated cathedral of its time.

So it was to be a mark of the greatness of Paris,

as one of the largest

and most economically successful cities

in Europe at the time.

- [Narrator] But beneath its Gothic splendor

lie deep mysteries of its construction.

- It's not only the scale that amazes,

but the innovative techniques

used to achieve such heights.

- [Narrator] And the structural mysteries

are just the beginning.

- Legend has it that the gargoyles

are the protectors of the church.

But are they protecting the church

against supernatural forces or against earthly threats?

- [Narrator] Beneath the soaring arches of Notre Dame

lies a secret that stretches back

to the very foundations of Paris.

- For generations, pilgrims and tourists

have marveled at the Christian masterpiece

that is the Notre Dame today.

But few realize that the ground

that touches their feet holds clues

to a much older, grander, mysterious past.

- They find stone structures underneath Notre Dame

that would predate it by centuries.

- In the 1700s, they discovered that the church

was built on the ruins of an old Gallo-Roman temple

to Jupiter, the king of the Roman pantheon.

- What does that tell us?

Well, first of all, that you have a temple

to the most powerful of the Roman gods,

suggests that this place,

the place where it's located,

has long been a site of cultic worship,

and in particular, a very sacred site.

- This is evidence of the site's long history

as a place of worship.

How did a pagan temple become

one of Christianity's most revered cathedrals?

- [Narrator] The transformation from pagan temple

to Christian cathedral was a centuries-long process.

- As Christianity spreads throughout Europe,

the site undergoes a radical metamorphosis.

- Sacred sites tended to remain sacred sites

even when there was a change in religion,

and so the Christians didn't seem to have a problem

rededicating pagan holy sites

and making them Christian holy sites.

- So we go from the pagan temple

to an early Christian church,

and that gets replaced by another Christian church,

but it stays in a line of descent

that eventually brings us to Notre Dame.

- [Narrator] Emerging from the shadows

of its pagan origins,

Notre Dame Cathedral has defied centuries

of challenges and natural disasters.

What architectural secrets lie

within its hallowed walls,

enabling the Gothic structure

to withstand the ravages of time and nature?

For centuries, Notre Dame Cathedral

has stood as a testament to Gothic architecture.

But in 2019, a devastating fire engulfed the cathedral,

destroying its roof and iconic spire.

- To see a structure like this be impacted by the fire,

it's a little heartbreaking for a structural engineer.

I remember we turned it on at our office and watched it.

- [Narrator] As the smoke clears,

archeologists and historians

are given an unprecedented opportunity

to study the inner workings of Notre Dame's structure.

- What hidden resilience did medieval builders embed

within the very bones of Notre Dame Cathedral?

- [Narrator] One of the keys to the cathedral's longevity

could be the 30 flying buttresses

that form its stone exoskeleton.

- When we start building big structures like Notre Dame

with large, open indoor spaces,

we end up with immense roof structures that are very heavy.

And the result forces from those roof structures

invariably want to cause our walls to buckle outward.

So we need to design systems that support our walls.

And with Notre Dame,

that technology is the flying buttress.

- The walls are quite tall,

so they're a little wobbly.

You can imagine building a wall out of Lego.

At some point, it's not very stable,

you can't put another brick on top of there.

And so you need to brace it horizontally.

And that's where the flying buttresses come in.

They are lateral supports at high up points

that then take those lateral forces out,

and all the way down into the ground.

Also, when you have an arched roof,

that arch wants to thrust out at its haunches.

And so the arch itself is imposing a horizontal force.

That force goes into the flying buttresses.

So all these things are tied together

and they are integral to that building.

If you do not have the flying buttresses,

that building will collapse.

It's amazing to see this ancient engineering,

and how they knew this, and used arches,

which are another really strong shape

in these flying buttresses

to make them lighter and functional.

- [Narrator] As restoration work

on the burned cathedral begins,

a remarkable discovery is made within its stonework,

large iron staples are revealed,

measuring up to 50 centimeters long.

These staples found throughout the cathedral

bind stones together, providing reinforcement

that allows it to achieve its impressive 35 meter height

while maintaining a light, slender appearance.

But the true breakthrough comes

when these iron reinforcements are dated.

Radiocarbon dating reveals they originate from the 1160s,

making Notre Dame the first known Gothic cathedral

to use iron extensively throughout its structure,

a feat not repeated for about four decades.

But these iron reinforcements

aren't the only metalwork hiding secrets

in Notre Dame's walls.

Adorning the massive western doors of the cathedral

is intricate ironwork,

and with it, comes a legend of devilish intrigue.

- There's so many legends

about the building of Notre Dame,

but there's one from the 13th century

about a young blacksmith named Biscornet.

According to legend, he had been commissioned

to complete the elaborate,

ornate iron doors for the cathedral.

- [Narrator] But when the completed doors are unveiled,

people are astounded.

- The level of craftsmanship was unprecedented.

The intricate details and artistry are so advanced

that it leaves people in disbelief.

- No one believes it could be the work

of a 13th-century blacksmith.

- [Narrator] This leads to wild speculation.

Biscornet's work must have been the result

of a deal made with the devil.

- Rumors begin to circulate that Biscornet

had been found in his workshop unconscious,

and that the iron doors

had miraculously been completed overnight.

When it came time to open up the doors, they were stuck.

According to legend,

it was only after the application of holy water

that they were able to be opened.

- Adding to the mystery, Biscornet reportedly dies

shortly after completing the project.

(dramatic music)

- For people at the time,

the battle between good and evil

was a real live one.

So actually, it wasn't a huge leap of the imagination

to believe that these beautiful iron doors

were inspired by the devil.

The story comes out

that it's supernatural powers that did it.

And yet the minds of the people around

turn to it not being divine intervention,

but instead to it being the devil.

- It's not surprising, in a way,

that a church of this grandeur

would attract demonic tales.

It is constructed as a bastion of the Christian faith,

which means, of course,

demons will want to play with it,

they will want to haunt it,

they will want to torment those who go there.

So in that sense,

the fact that it's spiritually significant

means that it will be a obvious target of the demonic.

- [Narrator] To this day,

the legend of the devil doors persists.

- And interestingly, modern blacksmiths

can't actually explain how those doors were constructed.

- [Narrator] Whether crafted by human hands

or through more sinister means,

the devil doors continue to hold their secrets tight

at ground level.

But perched up above,

Notre Dame's silent sentinels stand watch.

What ancient mysteries do these grotesque figures conceal?

- The gargoyles of Notre Dame are iconic.

They are monstrous,

with bulging eyes and sharp teeth.

- As a visitor, you arrive and you look up

and you see these enormous winged creatures perched,

looking down at you,

each with its own individual personality and movement.

- What's striking about these gargoyles

is the wide variety of design in which they were made.

And yet, what unifies them

is their whimsical, fiendish,

almost devilish nature.

- These aren't just decorations.

These gargoyles have stood watch

over the cathedral for centuries.

- There are a number of theories

about what they might have been intended to do.

Perhaps the most popular one is that they were protective,

that they were looking over Notre Dame,

and its parishioners with an eye out

to defeating any demons that might be circling.

- Others see them as representations of sin and vice,

lurking outside the sanctity of the church.

- If you look beautiful,

people think you can do no wrong,

that you are good,

that you're special just by that looks.

And, therefore, the flip side is also there.

If you look ugly, if you look grotesque,

then you're a monster and you're evil.

And that's why when we look at these gargoyles now,

we see them as evil creatures.

- And there are so many folklore and stories

associated with them.

One story goes that the gargoyles come alive at night

and patrol the streets of Paris,

keeping us all safe from harm.

- Another tale suggests

that these gargoyles aren't sculptures at all,

but monsters turned to stone by the power of the church.

- [Narrator] The gargoyles adorning Notre Dame today

are not medieval originals, but 19th-century additions.

Many of the original gargoyles

fell victim to the French Revolution's destruction

in the late 1700s.

Over the decades following the Revolution,

the cathedral falls into disrepair.

But it would receive a new lease on life

thanks to French author,

Victor Hugo's 1831 novel "Notre-Dame de Paris",

whose 1833 English translation

was known as "The Hunchback of Notre Dame".

- Victor Hugo's novel really raised the cathedral

in popular consciousness,

and led to a surge of interest

in restoring the cathedral to its former glory.

- [Narrator] A renovation under the guidance

of architect, Eugene Viollet-le-Duc,

began in the 1840s,

and new gargoyles were crafted,

cementing Notre Dame's status as a cultural icon,

and popularizing the notion of gargoyles

as the cathedral's guardians.

But the true purpose of these figures

is actually crucial to the cathedral's structural integrity.

- In reality, their function is much more practical.

They serve as water spouts,

channeling rainwater away from the building's walls

to prevent erosion.

- [Narrator] Following the tragic fire

that swept through Notre Dame Cathedral in April, 2019,

the gargoyles and grotesques have come to embody

the enduring spirit of this beloved landmark.

- When we think about Notre Dame now,

and the fact that it's now rebuilt,

it makes us realize that monuments are not static.

They are constantly being remade

and repurposed and reused

by the cultures because they cherish them,

because of their ties to their historic past,

but also because they're living spaces,

living histories, that are still meaningful to them.

- [Narrator] The cathedral reopened in December of 2024

after a nearly five-year restoration,

that was not without its challenges.

- Structures that have caught on fire,

some of them aren't salvageable.

This one, though, being stone,

is far more salvageable

than a wood structure would have been.

But in terms of the tools and the know-how

and the knowledge, and the ability

to rebuild something like this,

and not everybody can do that,

there's less and less people

who could build these structures in a similar way,

with the expertise and with the knowledge.

- While some have attributed the marvels of Notre Dame

to supernatural evil forces,

the reality is that Notre Dame represents

the pinnacle of human ingenuity, skill, craftsmanship,

and the determination of a people in their time.

The real magic of Notre Dame

is the medieval craftsmen that made it.

(dramatic music)

- [Narrator] From the whispers of otherworldly forces

at Sacsayhuaman, to the tales of djinns at Chand Baori,

and the ominous devil doors at Notre Dame,

the stories of these architectural wonders

blur the line between human achievement

and the supernatural.

While standing testament to remarkable engineering,

they hint at forces beyond our understanding.

What hidden truths

might these ancient structures still hold,

waiting to be uncovered by future generations?

(dramatic music)

(dramatic music continues)