All language subtitles for NOVA.S47E16.Saving.Notre.Dame.1080p.AMZN.WEB-DL.DDP.2.0.H.264-GNOME_track3_[eng]

Notre Dame de Paris...

a treasured icon of
Gothic architecture

and medieval engineering,

built from glass,

stone,

and timber over the course

of two centuries.

For 850 years, this
226-foot-tall cathedral

has been an enduring
symbol at the heart

of French culture, and more...

Notre Dame
is one of humanity's greatest

artistic and architectural
achievements.

Notre Dame is not just Paris.

It's France.

And beyond France,

it's the world.

But on April 15, 2019,

a disaster that threatens
to destroy it all strikes.

A massive fire
raging out of control...

Oh, my God!

Leaves the cathedral in ruins.

Now, an elite team of engineers,

scientists,

and master craftspeople,

battle to save this
fragile structure

from a catastrophic collapse.

Out of tragedy,
an opportunity is born...

Oh!

This is a dating fossil.

To solve
archaeological mysteries

and understand the very fabric

of this medieval megastructure

like never before.

We can
identify each chemical element.

Can clues from the past

help save and
rebuild this landmark?

And can pioneering technology

prevent another disaster?

What we are producing today

will be the information
usable for the next generations.

"Saving Notre Dame"...

right now, on "NOVA."

Major funding for
"NOVA" is provided by the following:

The Cathedral
of Notre Dame de Paris...

an 850-year-old Gothic wonder.

It's the heart of France.

The distance from
Paris to all other places

is traditionally measured
from this iconic structure.

There is a continuation,

a historical continuation,

from the Middle
Ages to nowadays.

And it's very important
to build a kind of identity.

Notre Dame is one
of the monuments

which achieved this identity.

For Christians, it's a
place of worship, right?

And, and for those of
us with different beliefs,

it's one of just this incredible
artistic and historic landmark.

You've had coronations there,

you've had the crowning of
Napoleon and King Henry.

There's just so much attached

to the cathedral.

But Notre
Dame is much more than that.

It's also a pinnacle of
medieval engineering.

The cathedral can
hold 9,000 worshipers,

and its 100-foot tall walls

contain more than 32,000
square feet of stained glass.

The ceiling is a series
of domed Gothic vaults

that hold up the
cathedral from the inside.

A complex 550-ton web of timber

forms a cross-shaped roof,

topped with 1,300 lead tiles

and a 300-foot
tall central spire.

Wrapped around the church
are 28 flying buttresses,

limestone arches that brace
the walls from the outside.

And at the front,
two mighty towers,

with ten massive
bronze bells inside,

soar over 226 feet
into the sky over Paris.

The construction
took many generations.

Architecture was not
learned at the university,

so the architects and all
workers learned mostly on site.

Along the way,
there were many setbacks.

In 1789, at the height
of the French Revolution,

anti-Catholic forces

destroy parts of the Cathedral.

A newly secular France
leaves Notre Dame

in a state of neglect.

But when Victor Hugo writes
"The Hunchback of Notre Dame"

in 1831, it sparks a
$60 million restoration,

that tops out the
cathedral with a new roof

and a 750-ton
timber and lead spire.

Periodic renovations
continue to this day.

On April 15, 2019,

Notre Dame is wrapped
in 550 tons of scaffolding,

as workers begin

a $6 million operation to
shore up the cathedral's spire.

CHAUVET AND MADO:

Notre Dame's rector,

Father Patrick Chauvet,

has finished evening worship.

His world is about to
be turned upside down.

I stopped here because

I really like Mado.

She offered me a drink, and
when she came back she said,

"Father, there's smoke above
the spire of the cathedral."

So I left my drink and went
back to check there was nobody

in the cathedral.

At 6:18 p.m.,
a sensor detects smoke

in the medieval roof timbers.

The system sends a coded
fire alert to the security team.

Instead of heading
straight for the roof,

a guard is dispatched to
the sacristy building nearby,

to check for a fire.

But he finds nothing.

He climbs up into
the church attic.

But by the time he
gets there, he's too late.

The fire has been burning
for almost 30 minutes

and has spread across the roof.

And there was this horrifyingly

huge plume of smoke
billowing up out of it.

It was surreal.

I'd never seen
anything like that before.

You saw the fire trucks come up

alongside the cathedral
and ladders went up,

and the hoses came out,
you could see that the ladders

were just too small for
a building of this size

and the hoses were
not nearly big enough

for this kind of blaze.

It was tragic; the resources

that were available
were not going to be

what was needed to bring
this thing under control.

A lot of us realized

that this fire was just going
to ravage the cathedral.

We saw what was happening,

but we were powerless,

we could do nothing.

It really looked like
the end of the world.

It was so chaotic.

A delay in responding
to a fire of this nature

is absolutely critical.

A small fire burning locally
is a very different thing

than ten minutes later when
all of the timber elements

are involved.

So in a situation like this,

five, ten, 30 minutes can
make all the difference.

This delay
will have huge repercussions.

As firefighters arrive on scene,

so does one of
France's chief architects

of historic monuments,

Rémi Fromont.

I managed
to pass the police checkpoint

and I joined the firefighters.

As the inferno
rages at the top of the cathedral,

Rémi risks his life
to venture inside

with the firefighters.

We did a tour
of the cathedral several times.

We checked the nave.

I saw the flames
and saw the blaze.

I gave them all the
advice that I could.

Within minutes, the
firefighters are pumping tons of water

into the roof space,

but to no avail.

To the horror of
the growing crowd,

the fire engulfs
the iconic spire.

The world watches helplessly

as the 750 ton oak and
lead masterpiece gives way.

Oh, my God!

Oh, my God...

That is awful.

When the spire

fell into the roof,
additional ventilation

will have caused
more oxygen-rich air

to be sucked in at the
bottom of the compartment.

That influx of oxygen

could have caused an
increase in the severity of the fire

within Notre Dame.

All of a sudden,
there was a huge, huge ball of fire

rising out of the cathedral.

It was spitting ash and debris
everywhere, so we took shelter.

It was just
devastating to watch.

We were suddenly really aware

that of, of how easily this
whole thing could come down.

90 minutes
after the fire begins,

the entire roof of the
cathedral is ablaze.

Inside, it's become even
more dangerous for Rémi

and the firefighters.

Getting this fire under
control looks impossible.

The fire on the ground,

smoke everywhere,
a hole in the ceiling.

We were trying to
understand what was going on,

where the problems where,
check what had collapsed

and if there were other risks.

- A
- southeasterly wind picks up

and pushes the blaze
towards the famous bell towers.

If the bell towers catch fire,

and the bells fall,

then they will smash
through everything below.

Inside the
ingeniously engineered

13th century north tower

a scaffold of wooden
beams holds eight bells.

The biggest weighing
more than four tons.

If the beams burn through,

they'll spark a
fatal chain reaction,

causing the bells to
fall like wrecking balls,

destroying the tower's
wooden backbone.

If the tower falls, it could
trigger a deadly domino effect

that brings down
the entire cathedral.

To avert this
catastrophic collapse,

the firefighters have no option

but to venture deeper inside.

President Macron said: "No doubt,

we must send
the firefighters in.

The cathedral must be saved."

We headed to the North tower

just when the flames
had reached the belfry.

The firefighters
also knew it well.

We were guiding each other.

To douse the fire
on the roof, firefighters pump water

from the River Seine
and feed it to fire trucks

around the cathedral.

But to stop the towers
collapsing they must send a team

into the burning structure.

Their mission: drop hoses
in between the towers

and fight the fire
spreading from the roof.

But the steady
wind doesn't let up.

And despite their efforts, the
timber frame holding the bells

has caught fire and could
trigger the destruction

of the cathedral at any moment.

So the team must drag their
hoses to the top of the tower

and soak the timber frame
to prevent the unthinkable.

Throughout the night,

the fate of Notre Dame
hangs in the balance.

Eventually the firefighters
get the upper hand.

The flames have been beaten
back and only glowing embers

light up the night sky.

Nobody knows
how the fire started.

An investigation begins.

But for now, the
urgent question:

how damaged is the structure

and can it ever be rebuilt?

President Macron pledges
to restore the cathedral

in five years.

Tonight, I
tell you very solemnly,

we will rebuild this
cathedral together.

Meanwhile, the
world keeps vigil for Notre Dame.

Daylight reveals the full extent

of the terrible destruction
wrought by the fire.

The oak roof and spire
are completely destroyed.

Tons of toxic lead
that covered the roof

have been sprayed into the air,

contaminating the site.

Burned roof timbers
cover the vaulting.

Three gaping holes
in the stone vaults

weaken the entire structure.

And the 550 ton scorched
carcass of scaffolding

could collapse at any moment,

something unthinkable to
those tasked with preserving

France's rich cultural heritage.

PHILLIPE VILLENEUVE
I'm in front of my cathedral,

which is in this state.

I need to work.

Phillipe Villeneuve is in charge

of historic monuments in France.

This is the cathedral
that inspired him

to become an architect.

I must have been five

or six years old.

My parents brought
me here one day,

like every child from Paris.

I was fascinated
by the architecture.

It stayed with me since.

Since 2013,
Phillipe has been responsible

for conserving Notre Dame.

It was the culmination

of a dream.

A dream come true.

Today that dream has
turned into a nightmare.

The stricken
cathedral is a giant house of cards.

If the stone vaulting collapses

the weight of the buttresses
will push in the 100-foot walls.

And Notre Dame will be no more.

So Phillipe
heads up a rapid response team...

dozens of engineers,

architects, and scientists.

Their task is to prevent a
total collapse of the cathedral.

From the bottom of my heart,

I want to thank you all for
your dedication, your approach,

your passion.

You are doing a very
difficult job, which is essential

for the cathedral.

It's not only a difficult job,

it's also hazardous.

The crumbling stone vaults

and twisted scaffolding
make any visit

inside to investigate the
stability of the structure

extremely dangerous.

On the vaults we
have the problem of the impact

of the fire, but we will
also have to evaluate

the impact of the water
used to put out the fire.

And we can
see from here the inside of...

Go out.

The scaffolding is moving.

Scaffolding!

Motion sensors
are installed in the melted jumble

of scaffolding overhead.

These can be triggered
by gusts of wind...

a warning before a
possible full-scale collapse.

It's the alarm,
because the scaffolding has moved.

We must leave.

There are evacuations
like this each week; necessary,

but an impediment
to the urgent work

of stabilizing the structure.

It's very difficult
to juggle all these issues.

The problem is that we have
to take action very quickly.

But we need to consider

the reality of this building.

It's still in danger
of collapse.

We are still in the
stabilization phase

of the cathedral.

To avert
a catastrophic collapse,

engineers could build a
steel skeleton inside the nave

to brace the walls.

Then, even if the
vaulting caves in,

the walls of Notre Dame
would stay standing.

But it's far too dangerous
for workers to erect steelwork

beneath the
compromised structure.

We cannot go under the
vaults because we don't know

whether they'll fall or not.

So, instead of
bracing the walls from the inside,

the team will
build timber frames

under the buttresses outside.

Now, if the vaulting does fall
in, the buttresses can't push

on the walls, and they
won't come tumbling down.

They are very difficult because

no flying buttress is
identical to another.

They are made to measure.

Workers
at this factory race to cut

and assemble around
250 tons of timber

to create the massive
supports Philippe's team needs

to prop up the vaults.

It's critical each
support fits perfectly

beneath each flying buttress

to hold its weight.

Working around
and inside this space

is a logistical nightmare.

210 tons of lead cladding
covered the cathedral roof.

This was mostly
melted during the fire,

and now toxic lead dust
covers every surface.

The worksite is
highly contaminated.

Until the site is cleaned,

team members must
wear full protective clothing

to pass into the
contaminated zone.

When leaving site,

they undress,

discard all clothing,

carefully wash equipment,

then shower themselves.

Only then can they go
back to the clean area

even for a lunch break.

It's
very difficult to endure for the workers

who have had to deal with
these procedures for months.

These regulations
are not normal.

But this whole
site is not normal.

But, finally, five months later,

all 28 flying buttresses
are locked in place

and the walls are safe.

Now they can turn
to the next challenge...

secure the melted
mass of scaffolding

that hangs precariously
over the cathedral.

The scaffold weighs
more than a jumbo jet,

and only rests on
four spindly legs.

The team plans to wrap three
massive steel lattice beams

around it to tie the fragile
upper parts together.

Then they'll build more
scaffolding either side

and lay steel beams across it.

That way workers can get
inside the stricken scaffolding

to help cut off its
50,000 steel poles,

a truly Herculean task.

Only then can the team
put up a temporary roof

to protect them
from the elements

while they rebuild Notre Dame.

It's going
to be an extremely dangerous operation.

The spire has disappeared,

but the scaffolding
is still there.

It moves a bit,
but it's still there.

While engineers
gear up to remove the scaffolding,

architect Rémi Fromont

and Livio De Luca

begin a groundbreaking
project that will combine

the investigative work
with new scientific analysis.

Their ambition is to create a
data-rich model of Notre Dame...

a digital twin.

The digital twin will embed
not only the geometric structure,

or the visual appearance
of the cathedral,

but also all the scientific
data coming from the studies.

For example, you can
click on a stone in the vault

and access to
all the information

about its physical properties
such as the provenance,

but also the mechanical behavior

within the entire structure.

Luckily for
Livio, a series of highly detailed

laser scans of the cathedral
have been conducted since 2006.

These are brought together in
this priceless 3D dynamic map

to show every stone, timber,
and iron nail in the structure,

across time, from the 12th
century to the present day.

This is an
unprecedented project.

The ambition is to collect all
the information from the past,

to pass it to the future.

There's very
little first-hand information

about the construction
of Notre Dame,

or the craftspeople
who built it.

In the wake of the fire,

new studies of the
cathedral's materials

could unlock these secrets.

This new data, once
included in the digital twin,

will provide a blueprint for
the restoration and rebuild.

Inside Notre Dame,

scientists begin to gather
data and investigate the damage

to treasured statues,

murals,

and windows.

The cathedral's most fragile
wonder, its stained glass,

dates back to the 13th century.

36 windows circled
the lower level,

42 around the middle level,
and 43 around the upper level.

The three famous Rose windows

span up to 42 feet in diameter

and are made up
of over 1,100 panels

of beautiful stained glass.

Miraculously, they
survive the fire intact.

But the intense heat that melted

the cathedral's
lead-covered roof

means that much of the glasswork

is now covered in a
layer of toxic lead powder.

Removing it could
damage the delicate glass

and be harmful to restorers.

It was really
painful to see the catastrophe on the TV.

I was looking to see what's
happen around the windows

and it was, of
course, totally difficult

to have a good idea
of what's happened.

There is a before
and after 15 April,

for historical
monuments, that's for sure.

Glass scientist Claudine Loisel

uses a handheld
digital microscope

to investigate the
levels of lead powder

on the stained glass.

She must then
formulate a strategy

to clean every single panel; a
vast decontamination program.

This window is in the
back of the cathedral,

in the lower level,
furthest from the inferno.

But it's still badly
contaminated.

Fortunately, these windows
have not been cleaned for 100 years,

so the lead has settled on top

of a dust layer, not
on the glass itself.

The first thick layer of
deposit was, we can say

has a small
protection in one way.

So we have just to
remove all the deposit,

to clean these windows
from the 19th century.

Claudine examines
deposits from windows around the cathedral.

The samples reveal vital clues

about the spread of
the lead contamination.

After the spire fell,

the cloud of dust, lead,
and different particle,

push in the other direction,

so we are a little bit more
protected in this area.

The windows of the
upper level, in the path of the lead cloud,

have been most contaminated.

The team takes out and
transports these panels

to this special laboratory

where they experiment
with ways to remove the lead.

First, Claudine uses a
precision vacuum cleaner

to remove the
hundred years of dust

and most of the lead
powder along with it.

So this is a good
way to protect the conservator.

You can control the action,
the pressure on the glass

and also on the painting.

Then she
uses water and cotton balls

to remove the last of the lead.

Of course,

you need scientific
evidence that it's working.

Claudine uses x-ray spectroscopy

to determine exactly
how many wipes it takes

to bring the lead
down to normal levels.

So we can identify each
chemical element we have in the material.

Too few
wipes and the lead will remain.

Too many wipes and restoration
will take longer than necessary.

Okay,

now the analysis is finished.

After five
wipes, Claudine checks to see

if the glass is decontaminated.

Okay, we have different
chemical element... calcium, iron,

and if we want
to see the lead...

there is no lead!

After nine months we can see

a good solution, a good
way to clean and to preserve

the stained glass
windows from Notre Dame.

The upper level
windows were not only in the path

of the lead cloud,

but also closest to the inferno.

Claudine hunts
for hairline cracks

caused by thermal shock,

the rapid heating and
cooling of the glass.

These cracks is due to the fire.

This is a recent cracks

and this is typical
thermal shock.

It looks like
the upper level stained glass

will need to be painstakingly
glued back together.

But inside Notre Dame,

the lower level
stained glass appears

to have survived unscathed.

And here we can
see we have a good stability,

adherence of the painting,

so there is absolutely
no thermal shock,

that's good news for us.

On site,

the teams of scientists

meet the engineers
and architects

to share their findings.

Once Claudine's team
has restored Notre Dame's glasswork

to its former
glory, they may use

a radical new
preservation technique

to safeguard it for
future generations.

It's being used on a huge
scale here, in northern England.

This is York Minster,

an 800-year-old
Gothic masterpiece

and home to the largest
expanse of medieval stained glass

in the U.K.,

the Great East Window.

It is one of the largest
windows ever made

anywhere in the medieval world.

We've got glass from
the 12th right through

to the 18th century in
quite significant quantities.

And it is really our national
treasure house of stained glass.

Engineers here
are completing a $12 million project

to protect York
Minster's stained glass

from harmful UV rays and the
corrosive effects of moisture.

In modern stained-glass
conservation,

we're really doing as
much as we can to keep

both surfaces of the historic
stained glass dry and stable,

and that's where our ventilated,

environmental protective
glazing comes into play.

You can see that I'm almost in.

I think it's just
this last bit here.

Matt Nickels is
installing this new conservation system.

He slots a protective
clear glass exterior frame

into the window opening.

This goes into the
original glazing groove,

where the medieval
glass would have been.

This protective glazing
prevents corrosive condensation

from forming on the
800-year-old stained glass

that will sit behind it.

The gap created means that

there's air circulation
running through.

And when you've
got air circulation,

it's regulating the temperature,

which means that there's
less moisture on the glass.

Each frame is custom
made and takes great skill to fit.

You don't
want to make it too small

because it's going to
obviously slide through.

No two windows are
gonna be the same.

With the outer panel installed,

they can reinstate the
layer of medieval glass.

They're actually
in fairly good condition

considering that they're
early 13th century.

There's always
the worry whenever

you're handling glass like this,

but you just got to make sure

that you're really,
really careful.

There's nothing quite like

seeing it with
sunlight behind it.

When you put it up like
this, it's quite magical, isn't it?

Techniques like this

offer a glimpse of how
scientists like Claudine

may eventually preserve
Notre Dame's glass.

This is the best way to
protect stained glass windows,

so it will be for sure an option

to protect the windows
for Notre Dame.

Had the vaulting collapsed

next to the windows,

the glass could have
been badly damaged.

But luckily, the stone vaulting,

which sits just under
the timber and lead roof,

protected the windows
from the inferno above.

When
the architects of the Middle Ages

constructed this vaulting,

they used it to separate
the timber frame of the roof

from the rest of the cathedral.

So the vaulting took the
shock of the falling timber

and the fire and the
firefighters' water.

The magnificent
vaulting was built to be resilient,

thanks to precise
medieval craftsmanship,

using over a thousand
cubic yards of limestone.

The arches work
together to support the roof

and stabilize the outer walls.

But the intense
heat from the fire

and the collapsing spire

took out 15% of
the stone vaulting.

Today, three 40-foot-wide holes

and several smaller gaps
mean the vaults could collapse

at any moment.

The team collects, stores
and catalogs the fallen stone

in this tent, located
alongside the cathedral.

They may be able to
use some of this stone

to reconstruct the vaults.

But it's clear they'll also
need to source new stone.

Notre Dame is made up of
many different types of limestone.

Medieval masons chose
hard limestone for the towers,

pillars, and outer walls to
build tall and hold up the roof.

For the sculptures, they chose
dense, fine-grained limestone,

that can be carved
with great detail.

And for the vaults they selected
softer, more porous limestone

that's light but strong.

If the team
rebuilding the vaults

pick a limestone
that is too heavy,

the new vaults may not
last as long as they should.

Geologist Lise Leroux

investigates what quarry
this stone came from.

We have some blocks coming from

the collapse of
the vault for study.

This detective
work will help the team source

replacement stone that shares
identical mechanical properties.

We have to verify.

The fallen vaulting
stone contains a rare micro-fossil

called orbitolites complanatus,

a kind of plankton.

Fossils like this are found
in just one layer of rock.

This will make
sourcing new stone

of the same type even trickier.

Can they use this
geological fingerprint

to discover the original
source of the vaulting stone?

To find out, Lise
and fellow Notre Dame scientist

Claudine Loisel venture
deep beneath Paris.

Hidden under the city streets
is a rich source of limestone,

a vast labyrinth
of quarry tunnels.

Lise and Claudine
enter this maze

two miles south of Notre
Dame in the famous Catacombs.

Oh!

In the late 18th century,

the quarries were
given a different purpose

and they housed bones
from old cemeteries,

which were inside the towns.

Cemeteries which were closed
at the end of the 18th century

for sanitary reasons.

Among the bones,

Lise and Claudine find traces
left by the medieval miners.

Here, the block's been removed

and we're left with this trace.

They then square off the sides,

and use it to build Notre Dame.

And the strata height here, it
dictates the height of the block

that can be extracted.

The blocks we see at
Notre Dame have this height.

So the quarry itself
puts a constraint

on the construction
of Notre Dame.

We have life and we have death.

Well, yes.

The upper level of the quarry

holds hard limestone with

large, well-preserved fossils.

These fossils are

more characteristic
of the limestones

used for the pillars,
the arch in Notre Dame.

But not for the vault.

Lise and Claudine hope to find

a match for the
soft vaulting stone

in the lower level
of the quarry.

Now to look if we can find

the specific micro-fossils.

I'm not sure, because
the surface is very rough

and it's not so clear because
of all of the state of the surface.

The limestone here is softer,

but Lise cannot see a
match for the rare micro-fossil

found in the Notre
Dame vaulting sample.

So, back in the lab,

she takes a closer look
at a sample of limestone

from the lower
level of the quarry.

These little fossils...

this one, this one,

this one...

are, in fact some
planktonic fossils,

which are called foraminifera.

It's not the
fossil signature she's looking for.

But then...

Oh!

This one here is
orbitolites complanatus.

This little planktonic
fossil is a dating fossil,

which match with the
stone coming from the vault.

It's a stratigraphic indicator,

characteristic from
the Middle Lutetian,

which is a geological
age of deposit.

Lise confirms the
origin of the Notre Dame vaulting stone.

It's quarried from
the deepest seams

of limestone beneath Paris.

Conclusive.

But what
about the harder limestone,

used by medieval masons to build

Notre Dame's load-bearing
pillars and arches?

Another micro fossil
signature confirms the origin

of this type as well.

The arches
are built with a hard stone...

with a resistant stone,
to support the vault.

And the vault itself

is logically constructed

with a lighter,
more porous stone.

And in the quarry
located in Paris,

we have this two kind of stone.

Medieval masons
knew exactly how to exploit

the varying
mechanical properties

of the limestone for Notre Dame;

knowledge passed down
through the generations.

Sourcing more of the
correct stone won't be easy...

the old quarries
are no longer active.

But engineers now know

what limestone to look for...

this will help them find a
match in quarries outside Paris.

Stone is not the
only raw material

that will need to be replaced

as engineers
reconstruct Notre Dame.

The timber roof was
also a medieval wonder.

It was constructed from
25,000 cubic feet of timber,

cut from 52 acres of oak...

that's approximately
1,300 trees.

For this reason, it was
known as "the forest."

Every single oak in
Notre Dame's forest

was handpicked for the
physical properties needed

in the roof structure...

from dense straight
oak for pillars,

to curved oak for
support arches.

But the fire burned
every beam in the forest.

Today, this intricate 550-ton
timber jigsaw lies in ruins.

We thought
this sublime roof would be here forever.

It was a big puzzle with beams

from different periods,

all the way back
to the 13th century.

And to see it suddenly

all burned, all mixed up...

Oh, it's very emotional.

It's very difficult.

Almost 60
tons of the precious roof timber

still lie precariously
on top of the vaults.

Despite the destruction,

every single beam holds
the history of Notre Dame.

It has deep
archaeological value.

It's vital that workers
forensically record

the position where
each beam fell,

before they remove them.

This helps them determine

where it originally sat
in the roof structure.

Now, these highly trained
rope access technicians

gear up to catalogue and clear

the charred timber
on the vaults.

It's not possible to
walk on the vaults,

because the structure
is very precarious.

They needed to

create a way to
access with ropes.

We need to wear a special mask

because of the lead
dust that we might inhale.

We label the timbers

and we mark them with a code

that the architects will

be able to identify.

The team
has their work cut out...

there are thousands
of separate pieces

of timber to catalog.

We are working day and night.

We have a lot of work to do.

They've already extracted

around 4,000 pieces.

Timber scientist
Catherine Lavier

begins painstaking
detective work to reveal

how Notre Dame's vast forest

was originally assembled

and could be rebuilt today.

Some pieces
were very well-preserved

because as you see
here, with different faces

and another piece of
wood is coming here,

with a wooden joint
here to assemble them.

And it's rather typical
from the medieval period.

And here,

you have a mark,

of carpenters.

So they are sure that this
piece with this piece are together.

It's very important
for carpenters.

They prepare the
wood on the ground

and after that,

they go to the roof
and reassemble again.

Every carpenter has
his own way to mark,

but in general it's based on

the Roman numbers,

but we can find some differences
between teams of carpenters.

We were very
surprised to find that

because I thought
everything will be destroyed.

And, finally, not.

The tree rings of
the timbers conceal further clues.

Each ring represents
one year of growth;

a time capsule of information

about the life of
the tree in that year.

Catherine analyzes core samples
from Notre Dame's roof trusses.

She measures each ring
to reveal the secret story

of some of the
original oak trees

the structure was made from.

This screen shows the size

of each ring I measured.

At the start of its life,

you see it has very,
very large rings,

which correspond
to very rapid growth.

Next, it looks
like it experienced

some more dramatic events,

some difficult years,

here, when the
rings are very thin,

This could be because
of too much rain,

not enough sun, and
not enough nutrients.

And then, the life
of the tree continues

until it's cut down,
around its 96th year.

Catherine is gaining new insight

into the types of trees
best suited to rebuild

the complex forest
of Notre Dame.

This extraordinary
challenge will require

around 1,300 oak trees,

craftspeople
versed in the lost art

of medieval carpentry practices,

and a blueprint for possibly
the most geometrically complex

timber structures in Europe.

The one person who can unlock

the lost forest's
geometrical secrets

is architect Rémi Fromont.

In 2014, Rémi
spent the entire year

mapping every
inch of the timber.

It was a magical place

to go in there;
there was a smell.

There was a very special
atmosphere of light.

We still had the traces
of tools also on the woods.

It sometimes seemed
like they only left yesterday.

We are collecting photographs,

3D point clouds,

and the physical and
chemical characterization

of all the materials.

The fire at Notre Dame

triggers a race across France

to 3D scan historical
monuments, inside and out.

These represent a
digital insurance policy

to preserve French heritage.

The laser bounces off
each contour in the room.

The machine then measures

the time it takes for
the laser to return.

Millions of measurements

form a cloud of data

called a "point cloud."

In 2016, researchers
used this same technology

to create a full point cloud

of Notre Dame's lost
timber roof structure.

This remarkable 3D scan will
combine with Rémi's 2014 survey,

in Livio's digital
twin for Notre Dame.

What we are producing today

will be probably the
information useful

for the next generations.

The team
now has the data they need

to rebuild the timber roof
with the exact same geometry.

The new oak needed

could come from
forests like this.

Almost a third of France

is covered with forest.

Oak is a vital
strategic resource

throughout the Middle
Ages and the Renaissance.

Vast forests are needed to
build cities and expand navies.

This is the Château de
Beaumesnil in Normandy.

It's a National
Historic Monument,

built on the site of

an 1,100-year-old castle.

It was built in seven years.

It's something extraordinary
for just seven years' work.

The château
has seen better days.

The curved beams
that hold up the roof

are close to collapse
and must be replaced.

The wood
grain has been cut through.

This weakens the support beam.

And then you see that the
beam is completely eaten away.

The wood is degraded,
eaten by the fungus.

The restoration work here

requires much of the
same skill and knowledge

it will take to rebuild
Notre Dame's lost forest.

The timber has been chosen
so the curve of the grain

perfectly matches the
curve of the new beam.

If you get a straight tree,

which has a
straight grain, and...

if you cut a curved piece,
piece of wood inside of this,

so here is the fiber, so
it can break, right there.

But if you take the
tree that's curved,

the fiber is like this.

So it cannot break.

You keep all of the
structural strength of the tree.

The carpenters use

an original beam as a template

to mark out the new
beam on the oak.

The carpenters
who built Notre Dame

would be familiar with
the tools this team uses

to hew the raw timber.

So after
you split most of the wood,

you use a broad-axe.

They have a single bevel,

long cutting edge,
and the handle is offset.

So...

if you're working,

as you go down, your hand here,

you see I'm not
hitting this sharp edge.

For skilled carpenters,

cutting Notre Dame's
roof timbers with axes,

compared to a modern sawmill,

will take roughly
twice the time;

possibly too long.

This curved oak will be

one of ten the
team needs to install

as part of the château
roof restoration.

It sits alongside this
400-year-old original beam.

This one was cut

probably 1635, '37,

and then this one 2020.

I hope our ancestors
are happy with this.

Just like the Notre Dame beams,

the Château's
original beam holds

messages from
the old carpenters.

It's
extraordinary to find all these marks.

It's very old and
at the same time,

it looks like it was
done yesterday.

French craftspeople

have the oak,

they have the skills, and
they have the plans required

to reconstruct Notre Dame's
vast forest of roof timbers.

It's over a year since the fire
ravaged Notre Dame cathedral,

and the investigators
have not pinpointed

the cause of the blaze.

Immense challenges and
uncertainties still lie ahead.

The building is not
yet out of danger.

Over the next 12 months,

engineers must remove
the melted scaffolding

and seal the cathedral
roof to make it watertight,

then stabilize the
weakened vaulting.

It's a monumental task.

And rebuilding
the entire cathedral

could take much longer than

the five years decreed
by President Macron.

Faced with such a drama,

thankfully there's hope.

We need faith for this project.

It's this building itself
that generates this faith...

even for atheists... and
that's something magical.

Architects around the world

have unleashed
their imaginations

to submit grand plans for what
the new spire above Notre Dame

could look like...

from mirrored roofs with
kaleidoscopic pinnacles,

and vast solar panels
powering nearby buildings,

to stained glass edifices that
will light up the Paris skyline.

However Notre Dame is rebuilt,

the unique collaboration
of architects and scientists

is rewriting how we understand

the very fabric of this
magnificent cathedral.

I think the fire in some ways

helped remind a lot of people

what an important part of
our sort of shared history

and shared culture this is.

Soon, a complete
digital twin of Notre Dame

should allow future
generations of craftspeople

to maintain, protect, and
faithfully rebuild Notre Dame,

preserving this world
treasure for all time.

I have only one obsession...

save the cathedral,
resurrect it,

and reopen it to the public.