Original subtitles

- [Narrator] From ancient temples to towering cathedrals,

humanity's deepest beliefs have given rise

to architectural marvels that defy imagination.

- How on earth is this possible?

- It's the type of building

that inspires movies and fairytales.

- You would not think that it was real.

- [Narrator] Faith, worship, and even fear

have inspired the creation of unbelievable sacred spaces,

each a testament to the power of devotion

and human ingenuity.

- It is the largest unreinforced concrete dome ever built.

- [Narrator] From the enduring mysteries of the Pantheon.

- How did they raise this gargantuan structure?

- [Narrator] To the gravity defying wonder

of Mont-Saint-Michel.

- It looks like it's literally floating on the water.

- [Narrator] We pull back the curtain

of how ancient builders channeled their reverence

into feats of engineering

that continue to captivate us today.

Pushing the boundaries of what seemed possible

in their quest to honor the divine.

- Tales of a divine visit

hint at the reason the gate survived.

- The Archangel Michael tells him;

you have to go set up a church and monastery on this island.

- It's conversion to Christianity,

and a church is what has saved it.

(uplifting music)

- [Narrator] At the heart of modern Rome

stands an engineering triumph.

A building of unparalleled design.

- You're walking through these sort of narrow,

typical modern Roman streets,

and all of a sudden, the Pantheon is just in front of you.

It just sneaks up on you. It's amazing.

- Laying eyes on the Pantheon today

evokes a real sense of wonder.

- It is a stunning architectural work,

a perfect dome with an oculus at the top.

- You are left wondering

how on earth they managed to construct it.

- [Narrator] Nearly two millennia after its construction,

the Pantheon remains unrivaled,

the sole structure of its immense scale and venerable age

to have survived intact into the modern era.

- It is such an advanced structure

that it took centuries for architects

to fully appreciate

and even attempt to replicate anything like it.

- The Pantheon has the largest unreinforced dome

in the history of the world.

- What engineering secrets

have enabled the Pantheon to prevail

while other structures built at the same time

have fallen into ruin?

- How did they raise this massive structure?

- Did these ancient Romans have an advanced knowledge

of math and physics?

- And what inspired the ancient Romans

to construct the Pantheon in the first place?

- Pantheon means all the gods.

So you'd think by its name,

it would be a temple of all the gods.

But it wasn't the normal thing to do,

so it's a bit of a mystery exactly what it was.

- In the early 1500s, Michelangelo,

one of the most influential and talented creators

in Western art history,

lays eyes on the Pantheon's dome and is awestruck.

He claims it to be angelic and not of human design.

- [Narrator] Over the course of history,

many have tried to emulate the magnificence

of the Pantheon's dome.

- Many modern structures have been inspired by the Pantheon,

including Saint Peter's Basilica, the US Capitol Building,

and the Jefferson Memorial.

- But none have been able to replicate it

on a scale of grandeur and size

that we see with the Pantheon.

- The sheer scale and complexity

of raising the Pantheon's dome

would have demanded an extraordinary investment

of resources, labor and ingenuity.

Who was responsible for making this happen?

(dramatic music)

- [Narrator] The bronze inscription

adorning the Pantheon's facade

offers an initial clue

towards unraveling the mystery of its true architect.

- Across the front of the Pantheon

is the famous inscription.

In English, it says, Marcus Agrippa, son of Lucius,

three times consul, made this.

- Marcus Agrippa was also important.

He was the consul of Rome,

which meant that he oversaw administrative life,

including the construction of monuments

which would be dedicated to Emperor Augustus.

- [Narrator] In 27 BCE,

Octavian Augustus becomes the first emperor of Rome,

marking the transition from the Roman Republic

to the Roman Empire.

- Julius Caesar had been ruled by a Senate.

Now we have his nephew Augustus, who would succeed him.

His legacy was constructing this new administrative rule

for the state

in which he, as the ruler, held supreme authority.

- For Augustus, the stakes here are immense.

(dramatic music)

- Augustus comes to power after decades of civil war

and establishes the Pax Romana, the Peace of Rome.

- [Narrator] His rule will be defined

by economic prosperity, stability,

and wide sweeping infrastructure development.

- Augustus tried to bring back traditional Roman values,

and one of the ways that traditional Roman values

were embodied visually was in the architecture of Rome.

- This was the beating heart

of this massive empire built on trade and military might.

The structures that were built

would not only serve the needs of Romans

but would also manifest his authority.

- [Narrator] At the heart of Augustus's vision

is the transformation of Rome,

reimagining the ancient capital

as a symbol of imperial grandeur and efficiency.

- There's a famous saying which goes,

Augustus found Rome brick and left it marble.

(dramatic music)

- [Narrator] For centuries, scholars and visitors alike

accepted the Pantheon's inscription at face value,

crediting construction of the Pantheon to Agrippa

during Augustus's reign.

- We put great importance

on inscriptions found in ancient monuments.

These markings provide crucial information

about the patronage, dating and purpose of the structure.

However, when it comes to the inscription on the Pantheon,

it has done more to confuse.

- [Narrator] This long held assumption

is challenged dramatically in 1892

when new archeological evidence emerges,

revealing a surprising truth.

In April 2020,

a massive sinkhole opens outside the Pantheon,

exposing a hidden archeological clue

buried beneath the city's ancient streets.

- They find ancient Roman paving stones

that date to the time of Agrippa.

- These appear to be the remnants of an earlier structure,

meaning that the Pantheon we see today

is actually a reconstruction built upon the foundations

of an earlier temple.

- [Narrator] Further archeological evidence

and historical record

reveals that Agrippa's Pantheon was destroyed

by a fire around 80 CE.

Emperor Domitian rebuilds it,

only to have it burned down again

in a lightning strike in 110 CE.

The one we see standing today

is completed a decade-and-a-half later in 125 CE.

- So if this isn't Agrippa's Pantheon,

then who built the structure

that we see in front of us today?

- The building, as it stands now, was built by Hadrian,

a much later emperor.

So why would Hadrian keep the inscription?

- [Narrator] The emperor Hadrian,

one of the most significant leaders of the ancient world,

rules the Roman Empire from 117 to 138 CE.

He would become known as one of the Five Good Emperors,

a term that highlights a time

when Rome was led by capable rulers

who prioritized the empire's wellbeing

over personal gain or dynasty.

- Hadrian's rule is characterized by a shift

from expansion to consolidation.

- He was a prolific builder

and his passion for architecture

led to numerous building projects in Rome

and across the Empire.

- He was someone who saw building as an important dimension

of manifesting imperial power locally.

- By Hadrian giving credit to Agrippa

for his original construction,

this is a throwback to a very prosperous and wonderful time

in the Roman Empire..

- It conveys the idea of continuity,

continuity in the legitimacy of this imperial rule

from the early Augustan dynasty now to this new dynasty,

of which Hadrian was a member.

- [Narrator] The question still remains:

how did the Roman engineers

achieve the seemingly impossible feat

of constructing and raising the Pantheon's massive dome?

- Standing in the middle of the Pantheon

and staring up at the dome not only hurts your neck

but leaves you speechless,

breathless as to the engineering and design skills involved.

- Did the Romans understand the laws

of basic Newtonian physics long before they were defined?

- Did the ancient Romans recognize

that the balance

between weight of the dome itself and its span

are absolutely inextricably linked?

The lighter the dome, the further you can span it.

- One of these hints lie in their unique use of material.

This material not only expands

their engineering capabilities

but helps them create structures

of unprecedented durability.

- The Pantheon is the living embodiment

of the Urbs Aeterna, the Eternal City.

And one of the reasons for its longevity

is a building technique that was so advanced for its time

that, in many ways,

it far surpasses what we use today, Roman concrete.

- [Narrator] For centuries,

scholars and engineers have been captivated

by the extraordinary durability of Roman concrete

while failing to uncover its secrets.

- Modern concrete can break down in as little was 50 years.

But more than a thousand years

after the Western Roman Empire crumbled to dust,

structures like the Pantheon are still standing.

How is this possible?

- The poets came to speak of Rome as the Eternal City

and its architecture was meant to reflect that.

- Why is it taken us over 2000 years to crack the code

on something that the Romans used so widely?

- [Narrator] Researchers had assumed

that the key to the ancient concrete's durability

lay in one ingredient,

a specific type of ash that was described

by architects and historians of that time.

- We're starting to understand

what makes Roman concrete so special.

So unlike concrete today, which uses sand,

the Romans used volcanic ash.

And when this volcanic ash was used as a filler

and mixed with lime,

it made the concrete incredibly strong.

- [Narrator] But recent investigations

have unveiled another component in the ancient Roman formula

that enables it to repair itself.

- The lime itself produces a very basic solution,

which leaves calcium hydroxide in water in pores

in the cement itself.

The volcanic ash material has a large content of silica.

Silica is sand, so if you get a crack in it,

what happens is the small amount of liquid water

which contains calcium hydroxide moves into that crack,

some of the silicates react with that calcium hydroxide

to produce more cementitious material again in the crack

and heal it back up.

So what the Romans actually created was a concrete

that's essentially self-healing.

- But how did Roman concrete enable the execution

of the Pantheon's revolutionary design?

The secret is in the strategic use of concrete.

- Really what we want to do in domes

is start out with a very thick base

and get thinner as we go up,

because the stresses of the amount of material

that we're actually supporting above

gets less and less as we go up,

so we can have thinner and thinner walls.

We actually get a structure

that's easier to build, is lighter,

and is also more resilient

because it doesn't have as much mass to start with.

- There are 140 coffers, which is a recessed square,

in the dome.

They're arranged in five concentric rows.

The coffers in the dome,

they might have been strategically placed

to reduce the material, to lighten that load of that dome.

- [Narrator] Despite these ingenious strategies,

a fundamental mystery persists.

How did the ancient Romans raise the colossal dome

to the height at which it stands

considering the rudimentary technology of their era?

- Do you build that dome on the ground

and then lift it into place?

Can you lift it up on a large platform

and then remove the platform?

Do you shore it up from the ground

and pour the concrete up high?

Do you build those walls first and put it in place?

There are lots of different ways

that you might approach this.

Which one is the most successful?

I'd really like to know.

- [Narrator] The name Pantheon itself

holds cryptic insights.

- What was the true intention

behind this architectural marvel?

Was it driven by reverence, obedience, or perhaps fear?

- The word Pantheon means all the gods.

It's a bit unusual to dedicate a temple to all the gods,

but the suggestion clearly is there.

And the structure is there too.

The dome meant to reflect the dome of the sky.

And so as a temple,

it was a microcosm of the world, of the universe.

- [Narrator] In ancient Rome,

the line between mortal emperor and divine deity

was often blurred.

- Romulus was the son of the war god Mars.

He was the first king of Rome,

and a legend developed that the site of the Pantheon

was the place where Romulus is deified

and ascends to heaven.

- [Narrator] But although it would become popular later on,

at the time when the original Pantheon was built,

deification of Roman leaders was not a common

or automatic practice.

- Over time,

we find emperors playing upon the symbols of divinity.

The idea that emperors are gods

does gradually penetrate Roman religious culture as well.

- According to one historical source,

Agrippa wanted to put a statue of Augustus

with the statues of the other gods inside the Pantheon,

but Augustus refused,

and so Agrippa put the statue of Augustus

outside the Pantheon itself in the portico out front.

But it still associated Augustus with the gods.

- [Narrator] Hadrian's reconstructed Pantheon

features a captivating architectural element

that provides an alternative perspective

on the building's true function, the oculus.

- The important part about the oculus

is that it needs to be located concentric with the dome,

to ensure that the stresses

that are experienced across the dome are all equal.

It can't be offset.

It really needs to be in that center.

Structurally, the oculus could have been filled in

with concrete material,

but that concrete material would have to be incredibly thin.

And so maybe there was constraints

around how thin could they get that concrete

before it was unable to be durable enough.

- [Narrator] Beyond the front doors of the Pantheon,

the nine meter wide opening

stands as the sole source of light.

More than just admitting sunlight,

it traces the sun's journey across the sky.

- One can imagine that walking into the Pantheon

that you would immediately feel

you were brought into an otherworldly space,

because the light

that comes through the oculus during the day

infuses the entire environment

with this very soft, glowing light.

It evokes a otherworldly space

through this play of light and dark.

- [Narrator] Recent research gives further credence

to the suggestion that the Pantheon was constructed

as a sophisticated solar calendar,

marking dates of great significance to the ancient Romans.

- The study draws parallels

between the temple structure and Roman-era sundials.

- For the past 2000 years,

if you happen to be in the Pantheon on April 21st,

the anniversary of the founding of Rome,

you're going to pay witness to an incredible spectacle

as light from the oculus comes streaming down,

focused directly on the main entrance.

It not only speaks to the incredible sophistication

of the engineering to even achieve that,

it also shows how much cultural importance

the ancient Romans placed on certain days.

- [Narrator] In the wake of Christianity's rise,

many magnificent temples and monuments of ancient Rome

faced a grim fate of neglect and abandonment.

- After several centuries

of being the center of spiritual life in Rome,

we find it falling into a long period of neglect.

In 609, it's Christianized and turned into a church,

and here again,

it becomes an important center of worship in Rome.

- [Narrator] The shift in religious paradigm

threatens to erase

much of the city's architectural heritage,

leaving many once revered structures vulnerable

to the ravages of time and changing cultural values.

- In the centuries that followed,

much of the old city of Rome will disappear.

Buildings will be dismantled, recycled into new buildings.

Others will simply disappear underground

but not the Pantheon.

The Pantheon, protected by its new status, will endure.

- What was it about this particular structure

that allowed it to prevail

when other monuments of its time did not?

- [Narrator] The newly restored church

is dedicated as the Church of Saint Mary and all Martyrs.

- The Pantheon remains to this day

the largest unreinforced dome structure in the world.

That itself is a lasting legacy.

Here we are, 2000 years later and it's still standing.

It is still remarkable.

It's a work of innovation in and of itself

that hasn't been replicated.

- We're very lucky to have a building

as unique as the Pantheon.

Regardless of what your beliefs are,

its conversion to Christianity

and a church is really what has saved it

and allowed us to still have access

to such an amazing architectural wonder today.

(gentle music)

- [Narrator] Off the coast of France stands a structure

that seems to defy the very laws of nature.

Reaching skyward in a daring testament

to humanity's ambitions to touch the heavens.

Much like the Pantheon,

it embodies our ancestors' relentless pursuit

of architectural and engineering ingenuity,

challenging the limits of human capability and imagination.

(gentle music)

- Mont-Saint-Michel is a sight to behold.

It looks like something straight out of a movie.

- This fantastical site

has been compared to a mythical fortress.

- It's a type of building

that inspires movies and fairytales.

- It has endured for over a thousand years,

defying powerful tides, treacherous quicksand,

harsh weather, and fierce sieges

and still stands proud.

- It looks as much like a fortress

than it does like a monastery.

- What we see today reflects over a thousand years

of construction and renovation.

- [Narrator] While Mont-Saint-Michel

has captivated imaginations with its legends and mysticism,

the true wonder lies in the still unanswered questions

surrounding the very real construction and endurance

of this wonder of the West.

- How did these medieval builders erect this abbey

on such a narrow pile of rock?

Why the complete rehauling

of the island's defensive structures,

and how did this incredible structure end up so isolated

out in the middle of the sea?

- [Narrator] According to legend,

the island's transformation into a place of worship

begins with a divine encounter in the year 708 CE,

when the bishop Aubert is visited by the Archangel Michael,

a celestial attendant

associated with courage and protection.

- According to popular tradition, in 708,

Bishop Aubert is visited by the Archangel Michael,

and the Archangel Michael tells him,

"You have to go set up a church and monastery

on this island."

And Aubert wakes up and he thinks,

"Well, that was just a dream,"

and he doesn't do anything about it.

Three times the Archangel Michael supposedly visits Aubert.

- After three visions, he pokes Aubert in the head,

leaving a hole in his skull.

This is enough to convince the bishop,

and he resolves to build the church.

- On October 16th, 709,

Bishop Aubert completes and consecrates the church,

marking the official founding of what we now know

as Mont-Saint-Michel.

As the story goes, Aubert dies just over a decade later,

and his remains are interred

beneath the oratory he established.

After a millennium of expansion and change,

in 1792, a man claims to possess the ancient bishop's skull,

marked with the divine wound

inflicted by the Archangel Michael.

Today, the skull is on full display

in the nearby town of Avranches.

But could it actually belong to Aubert?

While believers maintain this tale,

some skeptics suggest it may be the head of someone else,

the prominent hole showing evidence

of early medical procedures rather than a holy encounter.

- Stories like Aubert being visited by the Archangel Michael

are actually incredibly common.

It follows a tradition of hagiography.

Hagiography are the stories that are written about saints,

and it's where we get superheroes of sorts.

They have powers that are bestowed upon them by God.

A founding of an important monastery or church

always has much more impact,

if it's associated somehow with a superpower of sorts,

somehow with a saint, somehow with an intervention by God.

It makes the site all the more holy.

- [Narrator] With no physical remains

of Aubert's original structure existing today,

does the tale of his hand-built church hold any truth?

- Does the church really exist?

If it were to be uncovered,

what could it reveal about the island?

(dramatic music)

- [Narrator] In the 2000s,

the first ever analysis of bricks

from the chapel Notre-Dame-Sous-Terre

hopes to reveal fresh insight into Aubert's original shrine

more than a thousand years after it was erected.

- The goal is to date this chapel

to see if it is in fact the original.

- [Narrator] Employing a trifecta

of cutting-edge scientific techniques,

researchers delve into the secrets of the ancient structure.

Analyzing approximately 100 bricks,

their results promise to shed new lights

on the secret past of the chapel Notre-Dame-Sous-Terre.

- We look at what the bricks are made of,

and then we can match that with historical record

to try to marry up what time period they were made.

- [Narrator] The results indicate

that the chapel was constructed in two phases

during the 10th century,

one part in the first half and one in the second.

- One of the problems when historians or archeologists

are confronted with a structure

is that it has changed many times over the years,

and when we're trying to reconstruct what it was like

at any one period,

we're often left

with a very incomplete archeological record.

Pieces of old buildings are reused in new buildings.

That's where we need to turn to documentary evidence.

And so that's where historians play a role,

because we'll be going through the archives

looking for clues

that there was already Christian monastic activity

happening there.

- [Narrator] A stark contrast to the humble origins

of Aubert's original church,

the Abbey of Mont-Saint-Michel towers

approximately 80 meters above sea level.

Atop the Mont summit sits the transept crossing,

the central point of the structure

representing the intersection of Earth and Divinity.

- One of the responsibilities of the church as a whole

was to make them both love and fear God at the same time,

and there's no better way to do that

than with impressive architecture.

So the whole Gothic architecture movement

is really a chance to communicate

to the lowest peasant and the highest noble

that God lives among us here,

and we all need to be better Christians.

- [Narrator] Situated at such a steep elevation, however,

the transept crossing is a daring architectural gamble.

Not only is this the symbolic heart of the abbey,

but it is vital

for distributing the weight of the church structure.

- Adding to the challenge is the fact

that this was built on essentially a precipice of rock.

It makes you wonder how did they get the labor force

to Mont-Saint-Michel?

How did they get their supplies

and materials needed to build and construct this building?

- [Narrator] With the potential

for catastrophic failure looming large,

one must ponder what compelling force or profound belief

would drive the builders

to undertake such a perilous and ambitious project.

- Pilgrimages happen

because Christians want to get in close proximity

to the relics of a holy person, a saint.

- To this day, the Benedictines in the abbey

claimed to have the skull of Bishop Aubert.

- Having an important saint in your monastery

can be a real moneymaker in the Middle Ages,

because these people are essentially paying to be there.

And Mont-Saint-Michel was really the second largest site

of pilgrimage in Europe

for a good period of the Middle Ages.

- It attracts scholars, artists, musicians and pilgrims

from across the continent.

- [Narrator] In 1060, Italian architect William De Volpiano

is chosen to build the main church

of the new Benedictine abbey.

- So when a monastic reformer like De Volpiano

is traveling around the continent and making these changes,

he's not unusual.

He is part of a larger trend of what's happening

in the 11th and 12th century.

It's this desire to standardize monasticism

and make it better,

desire to experiment with new forms of architecture.

And that's what's happening

when we come to Mont-Saint-Michel.

We have an effort to join in

in that larger trend that's happening to better the site.

- [Narrator] Using modern advanced technologies

like 3D scanning,

scientists are still uncovering exactly how he did this.

These ongoing studies

reveal labyrinths of concealed passageways

and previously unknown crypts.

But the key to erecting the majestic Benedictine church

atop Mont-Saint-Michel lay in four crucial ones.

- It is built on four crypts, which is highly unusual,

and these are intended to serve as foundations

on what is essentially a very precarious foundation

in this region.

- This is a dauntingly small rock bed,

only about ten meters in length.

- While this is a really narrow site to build on,

the best thing about it is that it's rock.

There are some challenges with working on rock.

Sometimes the rock might be quite an uneven surface

and you need to smooth that out.

- We kind of have to flatten the top of the hill off,

but we don't have the technology

to actually take the top of the hill off.

So what we do is we make small, flat areas

by cutting away the granite,

and then we place a portion of our foundation there,

and then we go up a little bit and cut another flat spot

into the rock and repeat that.

And then between each of those flat areas,

we start building these vaulted arches.

And we keep building vaulted arches upward

until we flatten the hilltop.

And then we can build our structure up from there.

- The layout and design of these crypts is carefully planned

to align with the structures above them.

- We really need, with large structures,

the ability to divide the weight and load of that building

over a large area.

And that's what the crypts are doing.

Clearly these people who are designing

and building this structure

recognize the need to move those loads and divide the loads

over the largest surface area of the hill

that we possibly can.

- [Narrator] Mont-Saint-Michel's battle scarred walls

reveal a fortress fortified by necessity.

- When we look at the archeological evidence

around the development of the structure

on Mont-Saint-Michel over time,

it clearly becomes increasingly more fortress-like.

- During the 13th and 14th centuries,

the heart of the village was situated at the top.

But over time, that village

has migrated down to the bottom of the mountain,

which is where we see it today.

- Mont-Saint-Michel was itself serving a political

as well as a religious purpose,

so that structure was necessary to be a place of safety

for those around them.

This was a purpose that we find

with many other religious institutions as well at this time.

It's not uncommon to find a monastery

that looks more like a fortress in some cases

than it does like a monastery.

(dramatic music)

- [Narrator] Captain Louis d'Estouteville

stands triumphant atop Mont-Saint-Michel,

having just vanquished his enemies

against overwhelming odds.

- In the 15th century,

Mont-Saint-Michel comes under a siege

that would last decades.

According to legend,

the sands around the fortress

are stained red with their blood.

This is the Hundred Years' War.

- The Hundred Years' War is a conflict

that at least gets started

because of a dynastic dispute in France.

But it's also really about the territorial ambitions

of both countries.

For the better part of 100 years,

these two countries will go to war with one another.

- [Narrator] Due to its proximity to the border

between Normandy and Brittany,

the stronghold became a key location

in this century-long conflict.

- During the Hundred Years' War,

it marked an important stronghold for the French,

one that they maintain throughout the war,

even when the English were at their highest point,

when they had routed French forces in many other locations,

Mont-Saint-Michel remained impenetrable.

- We do have one reminder of those efforts,

and that is in two bombard cannons that they left behind,

which are now affectionately known as Les Michelettes.

- [Narrator] In the 19th century,

renowned French writer and poet Victor Hugo

lays eyes upon Mont-Saint-Michel.

- Victor Hugo had gone to Mont-Saint-Michel

hoping for inspiration,

but instead what he found was utterly shocking.

- [Narrator] Hugo describes Mont-Saint-Michel:

"Around as far as the eye can reach, infinite space.

The blue horizon of the sea, the green horizon of the land.

Clouds, air, liberty, birds in full flight.

Ships with all sails set.

And then all at once

on the top of an old wall above our heads,

through a barred window, a pale face of a prisoner.

I have never felt so strongly as here the cruel antithesis

which men sometimes mix with nature."

- This once great medieval cultural center

had been reduced to a poorly-kept, brutal prison.

It was something that affected him profoundly,

and something that he vowed to change.

- How did this site of profound spiritual importance

become a place of confinement and punishment?

- In the late 15th century,

the French King Louis the XI-th figures out

that actually it's a great location

to send political prisoners.

- Many of the same physical characteristics

that made it a functioning

and long living Benedictine community

also lent itself to being a prison later on.

First of all, heavily fortified walls.

It was very difficult to access, especially at high tide,

and that meant it was hard to leave.

Internally, it's structured in terms of cells

that would already have had built in chambers

in which the monks would have lived.

So in that sense,

it was an easy way to use existing institutions.

- Famously, Louis the XI-th even designed a type of cage

that was put into use at Mont-Saint-Michel.

It was a metal box where prisoners would be locked inside,

and it was soundproof and they'd be hung from the ceilings.

- This soundproof contraption cut off the prisoner

from all human contact,

serving as a severe form of confinement

and psychological torment.

- We're used to experience the world around us

through our senses.

Now, you put somebody in this cage

where you can't hear or sense anything

from the inside of it,

you're cut out from the world around you.

This is probably as close as you can get

to simulating this feeling of no longer being alive,

no longer being part of the world.

- [Narrator] Adding to this profound isolation,

Mont-Saint-Michel today boasts some of the highest tides

in continental Europe.

- You know, at times it's an island.

At times, it's surrounded by quicksand.

- [Narrator] But, has it always been this way?

Ancient texts reveal a legend

that might unlock the secrets

of the tidal island's geological past.

- The story details that the Mont's surroundings

were once part of a dense and expansive forest,

home to a thriving village

that lived in harmony with nature.

After a great sin is committed by the villagers,

a tidal wave destroys the forest,

submerging it beneath the sea.

- The tide came in, washed the forest and the village away.

And from that point onward,

Mont-Saint-Michel is the way that we know it now,

surrounded by a turbulent ocean, alone in its isolation.

- [Narrator] While the enchanting story

has been passed down through the ages,

historical and geographical evidence suggests

it may be more rooted in folklore than fact,

leaving the true origins of Mont-Saint-Michel's landscape

shrouded in mystery.

Throughout history, the purpose and legacy of the structure

is rewritten with each wave that crashes against its shore.

- Now the monastery doesn't end then.

It continues, they're concurrent.

We have the royal prison,

and we have the monastery.

But over time, those things begin to change.

By the time we get to the French Revolution,

there's only a handful of monks there.

The revolutionary government that comes to power in France

with the French Revolution, of course, puts an end

to all monasteries in France,

and the prison now takes on a whole new form.

It's essentially the early modern equivalent of Alcatraz.

- And by 1863,

some 14,000 prisoners had passed by Mont-Saint-Michel.

Their very experience would be utterly discombobulating.

On the one hand,

they're living in horrid conditions,

suffering torture and punishment,

yet amid the most beautiful, awe inspiring surroundings.

- [Narrator] Victor Hugo's visit to Mont-Saint-Michel

impacts him profoundly.

He is inspired, along with other notable figures,

to campaign for the monument's preservation

and end its use as a prison.

In 1874, Mont-Saint-Michel

is converted to a protected site

and designated as a historical monument in France.

Just as Mont-Saint-Michel was shaped by devotion,

an ancient sentinel was preserved by it.

These structures, born of different eras and purposes,

share a common thread,

the enduring power of human conviction to shape our world.

Towering above the German town of Trier

stands an imposing remnant of the Roman Empire.

- The Porta Nigra

stands as a remarkably well-preserved testament

to Roman engineering.

It's the largest surviving Roman city gate

north of the Alps.

Its four-story structure

showcases the architectural mastery of ancient Rome.

- [Narrator] But for centuries,

details of the gate's past

have remained cloaked in obscurity.

- When you look at the Porta Nigra,

it's not like your prototypical gate.

It's a much more fierce looking structure,

and it has the nickname of the Black Gate.

- Porta Nigra is one of four city gates

surrounding Trier at the time,

and one of many across the Roman Empire.

So why is it the only one still standing?

Tales of a divine visit

hint at the real reason the gate survived.

- There's a story of a monk

that lived within the walls of the Porta Nigra.

And this is part of the reason

why we think it still stands today.

But who is this monk and where does the story come from?

- The Porta Nigra

is a very interesting example of these Roman gates

that were massive.

They were intended to be impressive.

- These are vital components of ancient infrastructure

and urban administration.

- Clearly they were important in general, of course,

for controlling movement in and out of cities, for example,

but they use them in many other ways

that speak to an interest in memorialization

and also as expressions of power.

- [Narrator] Unraveling Porta Nigra's place

in Trier's history

has proven an intricate challenge

úfor historians to solve.

Trier was founded by the Romans around 16 BCE,

during the reign of Emperor Augustus.

The city rose to prominence

when the Roman general Agrippa constructed a road

from Leon to Cologne in 39 BCE,

enhancing its importance as a trade and military center.

However, despite Trier's preservation

of numerous Roman monuments,

more than any other German city,

much of its early history remains shrouded in mystery.

- At one point it was turned into a church.

Then, after a period of time,

that part of the structure was demolished.

Other modifications as well

have sometimes got in the way of understanding its origins.

- Pinpointing its exact date of construction

presents a massive challenge.

- [Narrator] In 2017, researchers unveil new findings

that shed light on the timeline of this historical landmark.

- This carefully planned dig

aimed to answer the long standing question

of when exactly the Porta Nigra was built.

- [Narrator] After several attempts,

the team comes across an ancient piece of wood

that will prove key in unlocking the gate's mysteries.

Using tree ring dating,

they are able to tie the timber to the year 170 CE.

- It's quite rare to find wood in the archeological record.

The conditions have to be exact.

Most of the time the soil has to be not acidic,

more alkaline-rich as well as waterlogged

because the water keeps the wood from degrading.

- This discovery is a huge revelation.

- The city walls of Trier were constructed

during the reign of Emperor Marcus Aurelius,

which was a time of relative peace and prosperity

for the Roman Empire.

- If this is a time of relative peace,

why build such a defensive structure?

- [Narrator] The Porta Nigra was constructed

as part of a system of four city gates.

- Historical records, archeological evidence

and the remarkable preservation of the Porta Nigra itself

help us piece together what the original gate system

would have looked like.

- [Narrator] The gate's original design

featured twin four-story towers

flanking a central courtyard.

The courtyard separated the gate openings on each side,

creating multiple levels of protection and surveillance.

- So when we think about rocks and stone masonry,

historically we really couldn't cut them very accurately.

What makes sandstone an interesting material

for construction is that it's really formable.

So even with wooden tools with stone implements

on their end,

we can actually form sandstone into complex shapes

and form it very accurately.

Then when we place those blocks together,

even without mortar,

we end up with a really rigid, self-supporting structure.

- Interestingly, despite its grandeur,

the gate appears to be incomplete.

- Certain sections of the walls and pillars

appear to be very roughly finished,

which does not align with the precision of Roman building.

- Could looming events have interrupted its construction?

Or was it simply a matter of budget constraints?

- [Narrator] As a new millennium dawns,

Trier welcomes an unexpected visitor,

one who will alter the spiritual landscape of the city.

- So in 1030, a monk named Simeon arrives in the city.

He'd been traveling with an archbishop,

and he pretty much tried every way to be a monastic.

He'd been a monk in Egypt, in a monastery.

He'd been a hermit out in the desert.

None of those things had been extreme enough for Simeon.

And when he arrives in Trier,

he decides he's going to take it up a notch.

He's going to be an anchorite.

An anchorite is someone who essentially dies to the world.

They have themselves walled up permanently

in some sort of structure

where they can never leave ever again.

Usually there's a small space and opening

where food can be passed to them,

and where waste can be put out.

But that's it. They will never, ever leave again.

- He has access to great monasteries and abbeys,

so why would he choose this old Roman gate?

- Now the whole point of being an anchorite

is to be seen by other people being an anchorite.

It's the medieval equivalent of virtue signaling.

And so the location he chooses

has to be somewhere with a lot of traffic,

a place where people are going to notice him

being an anchorite.

So where does he choose, the Porta Nigra.

- [Narrator] Simeon's request to be enclosed in Porta Nigra

is granted,

and a ceremony is held

to mark the beginning of the monk's life as a recluse.

- During the ceremony,

he's enclosed in a cell high in the gate tower.

- It's irreversible.

Once you've made that choice,

there is no turning back.

You are living your life in that small, confined space.

- He spends his days in solitary devotion,

praying and fasting.

- For poor Simeon, it lasted a total of five years.

Five years. And he died.

And his bones were buried there in the same cell

where he had ended his days.

- This is part of the reason why we think

it still stands today,

because he spent time there, which enabled preservation.

- What motivated these monks to renounce this life

was both a quest to connect with God in their current life,

but also to be rewarded in the afterlife.

- [Narrator] Following Saint Simeon's death,

the ancient Roman Gate is expanded

to incorporate a magnificent medieval church

in the revered monk's honor.

- What we see today

has had its medieval iterations stripped away,

and it's basically reconstructed in its original form

to what people would have seen almost 2000 years ago

when they were approaching the gate.

- [Narrator] In 1803,

in the aftermath of the French Revolution,

Napoleon Bonaparte lays eyes on the Porta Nigra

and becomes intent on returning the monument

to its former Roman glory.

- It's very interesting and certainly revealing

that Napoleon, when he came and saw the Porta Nigra,

his first response was to destroy the attached church.

Now why would he want to do that?

That's because he wanted to evoke the imperial history

of the gate,

and the church was not part of it.

- Napoleon saw himself connected

to the Roman emperors of old.

And so the Porta Nigra,

rather than it being a medieval relic,

to Napoleon, it was a symbol of the great Roman past.

- Napoleon doesn't want to continue to fight

to build a new legacy

but instead appropriate a legacy that has already existed.

And in that sense, it's easier to build on.

It's sort of like momentum;

you start going back far enough

and it's easy to move forward.

But if you're starting from today, every step is a journey.

- [Narrator] Bonaparte dismantles the church and monastery

and today traces of the gate's religious extensions

are all but eliminated.

- One of the issues with sandstone

is it's really very porous.

So if you're burning fires in the Middle Ages

to keep yourself warm,

the smoke is going to impregnate,

especially the surfaces of the blocks.

And as we move into the industrial age,

we now have all of these industrial pollutants.

Essentially all of that pollution over many centuries

has absorbed into the sandstone over time,

and it's turned it from that natural sandstone color

into being very black.

- Given its imposing appearance,

it does give an allure to it

by being this standalone black gate that's just there,

waiting to meet visitors.

- [Narrator] A sense of wonder and mystery

will forever surround these monumental structures.

The Pantheon's dome whispering of forgotten deities,

Mont Saint-Michel's legends and visions

and celestial guidance,

and Porta Nigra's unfinished stories

echoing through the ages.

These architectural marvels

have revealed captivating secrets,

yet countless enigmas remain hidden within their stones.

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