All language subtitles for Rebuilding Notre Dame The Next

Notre-Dame de Paris,

a treasured icon of Gothic architecture

and medieval construction.

The feat of engineering in those days,
just extraordinary.

It is one of the most important
monuments in France.

But on the 15th of April 2019,

disaster strikes.

A huge fire rips through the cathedral,

reducing the roof and spire to ashes.

For the last 3 years,

our cameras have been following teams

of mastercraft's people and engineers

as they battled to bring
Notre Dame back to life.

Wow.

This is amazing.

I've been given
an astonishing opportunity

to visit the work site
here at Notre Dame

and this is such a critical time
for the team.

They've met the challenge of
making the structure secure

and now they're moving on
towards rebuilding it.

Hundreds of workers here
are locked in an ambitious race

to restore this medieval masterpiece

in time for a grand reopening
ahead of the Paris Olympics in 2024.

Ooh, what have you got here?

As we track their progress,

we'll also meet the historians
and scientists

working to solve Notre Dame's
architectural mysteries.

- Have you seen this before?
- No, never.

It's a kind of walking
backwards in time.

What's this lady doing?
Is she riding upon a dragon?

They're revealing ancient technology
hidden for nearly 800 years.

We're dealing with unknown structures

that are so far unique
in Gothic Architecture

And struggling to save
the fragile fabric of the building.

The loss of material
is catastrophic for us.

Three years into this extraordinary

5-year restoration project

this is the next chapter

in the race to save
Notre-Dame Cathedral.

Paris,

a city of churches.

Basílicas,

and almost 2,000 historic monuments.

On the 15th of April 2019,

one of the city's most famous buildings,

the 850 year old Notre Dame de Paris

was undergoing a 5 million pound
restoration of its spire.

A fire broke out inside
the oak framework of the roof.

After 90 minutes,

the 360 ton timber and lead
spire gave way

and crashed through
the stone vaulting

causing catastrophic damage.

It's only thanks to the bravery
of the firefighters that night

that anything of the cathedral
survives at all.

And for weeks and
for months after that

its future still hung in the balance.

The roof and spire are completely gone

and there are three
gaping holes in the vaulting.

Teams of engineers raced

to install supports to shore up
the fragile structure

but the cathedral remained
open to the elements.

Rainwater saturated the vaults,

adding weight
to the weakened stonework

and increasing the chance of
a total collapse.

Before they could make
the structure watertight,

they had to remove 40,000

burnt and melted scaffolding poles,

left over from
the spire restoration.

Now, they've built
a temporary sliding roof.

It's called the big umbrella,

to keep the stonework dry.

The cathedral looks
very different today

than it did when I first visited.

I'm historian Lucy Worsley,
chief curator at Historical Palaces.

I first came here, age 16,
French exchange trip.

Here's a picture. Ah, so young!

And I remember
going through the doors

of Notre Dame for the very first time,

it was breathtaking.

It was one of the formative moments
that set me on my course

to wanting to spend
my working life with historic buildings.

That's why for me,

like for so many other people,

the night of the 15th of April 2019,

was such a horrible shock.

We still don't know how the fire started

but 3 years on,

the ambitious project to restore
the cathedral is being ramped up.

In recent months, the team here
has almost quadrupled,

bringing together ancient techniques
and modern engineering.

200 workers are now battling

to bring Notre Dame back to life.

The first time I came here,
after the fire,

it was devastating.

There was a real sense of tragic loss.

But now,

things are changing.
It's like a new chapter beginning.

The cathedral looks clean.

I can see many, many
people working away inside.

It's like the wounded old lady
is learning to walk again.

The French state has ruled

that Notre Dame will be rebuilt
exactly as it was before the fire.

Donors have contributed
700 million pounds towards this effort

but the task ahead is enormous.

The team must remove tons of toxic
lead dust left over from the fire.

Then, clean and restore

the fragile stained glass windows.

To reconstruct the roof identically

they must first fill the 3 gaping holes
in the stone vaulting

and rebuild the timber framework

from almost a thousand oak beams.

Then cover it with 3,000 square metres
of lead sheeting

before they can raise
the 65 metre high iconic spire...

finally, to make Notre Dame whole again.

Beyond rebuilding identically,

for conservationists,

restoration is all about preserving
the story of a monument.

Old buildings matter to us because

they embody not just our history

but also our future.

So there could be an
argument in conservation

that if you're conserving a building you
don't need it to be like the original.

You know the story
of the building

can best be told by showing
where the differences are,

how the building has
changed and responded

all across the centuries.

The challenge for the team right now

is to clear up tons of toxic lead dust.

As the lead on the roof melted

and the spire collapsed,

it was sucked inside the cathedral.

I've worn lots of different...

costumes, outfits,
for telly over the years.

Never quite one like this before.

Workers must put on
full protective clothing...

to pass into the dirty zone.

The way onto the site is actually...

through the shower.

This is the clean zone and
through there it's the dirty zone.

When you come out, you come through
the shower, too because everything
has to be washed.

All your equipment, all your clothes
and obviously yourself.

It's then just a short walk
into the cathedral itself.

Wow.

This is amazing.

I have never seen
this much scaffolding.

Goodness me. There's an army of people

marching about doing things.

It's freezing, it's really cold.

And it's dark and
there's banging and it's--

it's a bit like hell, actually.

This is quite the opposite of
what a church is normally like.

There's a lift going up into the nave.

My goodness, that's a lift
made out of scaffolding.

- Hello.
- Hello.

Deputy director of operations,
Jonathan Truillet.

coordinates the work to bring
Notre Dame back from the brink.

Jonathan, there's a huge amount
of scaffolding in the cathedral.

What what does it allow
your team to do?

The scaffolding not only allows access
to clean up the toxic lead dust

but also plays another critical role.

Before the fire, the vaulting

made from hundreds
of cubic metres of limestone,

supported the massive timber
and lead roof above.

But now the vaulting
is extremely fragile.

As the team begins
to repair the stonework,

it could trigger a collapse.

To avoid this, one of their first tasks

is to erect 52 timber support arches
beneath the vaulting

so that they can rebuild safely.

Installing them 33 metres
above the ground is no easy feat.

Well, can we take a closer look?

Thank you.

The scaffolding enables the team
to build a temporary floor,

so they can install
the timber supports.

The crane must lower each one
and a half ton ton support arch

down through the hole
in the vaulting.

Each support arch is fitted with steel
brackets to secure it in place.

Hydraulic jacks raise it to meet
the underside of the vaulting.

With the temporary supports
in position,

it's safe for me to take
the lift to the top floor.

Oh.

That was a mistake to look down.

Oh, look, here's the window.

We're at the level of the windows.

Wow. This is not normally how you
get to experience a cathedral.

This glass is so... rich.

So intense.

Oop.

We're now as high
as the lift can take us.

Close to the underside
of the shored up vaulting.

Oh, wow!

This is incredible. It's like
being in a timber barn.

This same technique
was used to build the vaults

850 years ago.

The scaffolding and supports
will stay in place

until the vaulting roof
and spire are rebuilt.

The scale of the support work is--
it's just astronomical.

It's incredible.

I noticed there's quite a lot of
fire extinguishers up here.

Now these gigantic timber supports
are in place underneath the arches,

the cathedral is structurally safe.

It's definitely not going to fall down.

Which means that the people
working here can move on

to restoring and rebuilding.

You can hear them
hard at it, as I speak.

And this is going to be
a real race against time

because they want to reopen
the cathedral by 2024.

All eyes will be on Paris

when the Olympic games
are held here in 2024.

President Macron has agreed

that the landmark must be
rebuilt within 5 years,

in time for a grand reopening
before the games begin.

But with the cathedral's vaults,
roof and spire to rebuild

and the entire site still contaminated
by lead dust from the fire,

the task seems near impossible.

To make the site safe the team must
remove all the toxic lead dust.

Clara is one of 40
decontamination specialists,

meticulously cleaning

all 6,000 square metres

of Notre Dame's vaulting,
walls, pillars and floors.

This is to keep you safe.
It cleans... cleans the air.

Yeah.

And where does all the lead dust
that you've collected go.

My vacuum.

Oh, into the--into the backpack.

- Yeah.
- Yeah.

With this equipment we only work
two hours and a half at a time

and we need to stop to take a break.

How long will it take to
clean the whole cathedral?

- There are different spaces of cleaning
- Yeah.

now we're in the first one.

Only the first phase.
More-more cleaning to come.

- Yeah.
- Oh, my goodness.

The vacuuming of the lead dust
will take 8 months.

Then the restorers can move on
to deep clean the stone.

My dream was to come here
and work here, it's an opportunity.

You-you never expect
to be working

in one of the most
important monuments

in France, so...

Your dream has come true.

I think you deserve
a cup of coffee now.

Well, I already have
three cups of coffee today.

Go enjoy your break.
You deserve it.

- Bye.
- Bye.

You know it's obviously tragic
that the cathedral burned

but I hadn't really
thought about this;

it's given opportunities

to young people,
to learn new skills like Clara

but wearing a vacuum
cleaner on your back

for two, four, six hours a day,

sucking up poisonous lead.

Hoo.

That's tough work.

In places you catch a glimpse

of how dramatically changed
Notre Dame will be after the cleaning.

Beneath the lead

and centuries of smoke
from the millions of candles,

lies pristine limestone.

This is how the cathedral
looked 850 years ago

and will again soon.

As the cleaning progresses,

crafts people and technicians,

from mural specialists
and glass historians

to metal scientists and carpenters,

get to work.

These are France's foremost
experts in their fields.

In charge of guiding this unprecedented

concentration of medieval knowledge,

are chief architects, Pascal Prunet

and Philippe Villeneuve.

But this team will need to
pull out all the stops

if they want to reopen
the cathedral in 2024.

In April 2019,

this was the heart of the inferno.

This is where the spire
fell down into the nave.

It's only when you get up here

that you appreciate the scale
of what happened.

And to rebuild that spire,
my goodness.

It's going to need a
tremendous amount of wood.

Above the stone vaulting,

Notre Dame's roof was
completely destroyed by the fire.

One of the most complex challenges
the team here now face

is entirely to rebuild

the 1,000 ton roof structure.

Remi Fromont is the chief architect

tasked with reconstructing
the medieval roof

which is known as the forest.

During a research project in 2014,

Remi manually measured

the dimensions of every
beam in the forest

to create a comprehensive
survey of Notre Dame's roof.

This allows them
to replicate it perfectly.

-- used 850 oaks

to reproduce the Gothic roof trusses.

The most intricate element,

the cathedral's iconic spire,

will be built from another 1,200 trees.

The spire was a 360 ton

engineering masterpiece.

Hidden beneath 16 copper statues

and 140 tons of lead sheeting.

With a complex skeleton
of oak beams,

some as long as 20 metres.

The secret of its strength,

a dense lattice of oak
tied into the rest of the roof,

supports the entire structure.

The spire came to be

the embodiment of the building
and of the Paris skyline.

Which took huge imagination
and levels of engineering

and creativity and architecture,
which is quite exceptional.

Identically reconstructing this
wooden wonder, is no simple task.

The market town of Chesterfield

bears witness to the perils
of building with green timber.

Its sports the 660 year old
crooked spire

at the parish church

could be due to beams that
have warped as they've dried.

For Notre Dame's spire,

this precarious lean
must be avoided at all costs.

In public and private
forests across France,

the hunt for 2,000 perfect
oaks for Notre Dame begins.

These will form part of France's
annual forest management quota.

One-third of the country,

65,000 square miles,

is covered by forests.

This team of forestier
has their work cut out.

They must source 60
flawless oaks for the spire

from this 8,000 acre forest.

On the other side of the clearing
another candidate emerges

but it must be wide enough
and tall enough

to form a spire beam.

Lumberjack, Ahmat Seerpan,

begins by making a cut

that will direct the tree
to fall into the clearing.

Notre Dame's medieval carpenters

etched Roman numerals
on their beams

to reassemble them correctly
up on the roof.

Today this team
attaches a bar code

to each oak destined
for the cathedral,

so they can track it from the forest

to its final position in the new spire.

It took the forestiers
several months

to complete their
painstaking search

to fill their quota of 60 trees
for the new spire.

Notre Dame's builders

did not only innovate with timber

they also pushed the limits of
what could be made with glass.

More than 3,000 square metres

of spectacular stained glass

circled the cathedral in three levels.

One of the things
I really remember

about coming to Notre Dame
for the first time

was the otherworldly light
from all the stained glass.

Today most of
the natural light's been

blocked out of the cathedral
by this huge scaffolding structure

but there's a silver lining.

The scaffolding gives experts
the chance to get up close

to Notre Dame's
astonishing rose windows.

This is the first time it's
been possible in 160 years.

It is a very unique opportunity

because we don't
see them again

in the same way. Never.

When you're so close
from the panels,

you have a kind of intimacy

with the work of art and

even you can see sometimes
the mistakes of the medieval painters.

The 3 rose windows date
from the 12th and 13th centuries

and together they're
made up of 1,100 panels.

Protected by the stone vaulting,

they survived the fire unscathed.

These kaleidoscopic wonders

are filled with depictions
of ancient legends

biblical scenes

and saints performing
incredible feats.

The panels have been
restored multiple times

over 800 years

as they've been damaged.

Like time capsules
they contain messages

passed down across the ages.

They also hold many
unsolved mysteries.

Glass historians Karine Boulanger
and Elisabeth Pillet

hope this access
will help them reveal

the secrets of the largest
window in Notre Dame,

the gigantic south rose window,

measuring 13 metres in diameter.

They're busy mapping
every shard of glass.

Karine, what's this lady doing?
Is she riding upon a dragon?

It's, um, Margaret,

she's tamed the dragon.

- She's tamed the dragon?
- Yeah.

I can see, she's telling it
"down dragon, down."

It's fabulous, I love it.

And you can tell me how old
this window is, can't you?

This is your super power.
- Yes, no way.

It's a 13th century glass

but there are some restorations,
of course.

You see the the colour
of the glass is different.

So, I'm guessing that
that bit there.

Yeah.

That looks like it's quite dark.
Is that medieval? - Yes, it is.

- All the red is medieval.
- Yes.

But if you look at this red here,
you see how different it is.

Oh, so that's-that's not medieval,
that...

No. It's 19th century.

You see, this one
is more translucent.

- It's like a jigsaw puzzle.
- Exactly.

It's not only the subtle
differences in colour,

the style of painting on the
stained glass changed over time.

Medieval glass painters

applied a solution of
copper and iron oxides

to the coloured glass before
it was baked to harden the paint.

The style evolved,

a 13th century painter

won't paint the same way as
a 15th century painter, obviously.

At the same time for the 19th century.

What causes the medieval glass
to go cloudy like that?

It's linked to the composition
of the glass itself.

In order to make glass,

- in 13th century, you use potash.
- Yes. - And it causes corrosion.

That potash, over 8 centuries,
corrodes like that.

Yes.

It's like a time limited
artwork, isn't it?

Yes.

Potash, a potassium-rich
blend of plant ashes

reduced the melting point of the
ingredients used to make glass.

By the 19th century,
sodium carbonate

combined with calcium oxide,
were used instead.

And produced more stable
glass that didn't corrode.

This factory, on the banks of
the Loire in southern France,

is one of the last
places in the world

that can produce stained glass
using medieval techniques.

We produce glass for
major historical buildings

as Versailles
or the White House.

Workers start by mixing sand,

metal oxide for colour,

sodium carbonate

and calcium.

They heat the mixture
to 1,300 degrees Celsius

and build up layers
of the molten glass

on the end of a blowing pipe.

The glass blower forms a sphere
from the red hot mass.

He rolls it to maintain this shape

which is critical to form
an even thickness of glass.

It's a manual know-how.

There is absolutely no machines

and the glassblowers
uses a sense,

a feeling,
to blow one glass sheet.

The team enlists the help of gravity,

they swing the 7 kilo ball of glass

in a 4 metre deep pit

so it elongates to form a tube.

Herve, has blown glass here
for more than 33 years.

Once cooled, they cut the cylinder

and send it to a special furnace
where it's unrolled.

Extreme heat of 750 degrees Celsius

and a wooden block

smooth out the glass
and minimise imperfections.

They carefully inspect each pane

and remove any rough edges.

Every glass sheet is different

and has the spirit
of the glass blower.

Losing this patrimoine and know-how
would be a disaster.

The factory marries these
ancient techniques

with the latest technology

to reproduce stained glass accurately.

We can fit perfectly

with the old colours

by using tools like

spectrophotometry,

like x-rays,

and this allows us to know exactly

what are the elements
that are in the glass

and reproduce it for the future.

By analysing samples of ancient glass

to learn the chemical composition,

they can match its unique
combination of metal oxides.

This team is ready with the skills

passed down through the centuries

to reproduce any of Notre Dame's
stained glass that may be beyond repair.

Until the 20th century
when a glass was

too badly damaged,

we had to replace it.

There are restorations every 50 years

or 100 years.

So, a stained glass window is
always a mixture of original glass,

here, 13th century glass

and restoration from...

every century almost.

As the historians map
the south rose window

they uncover an unusual trend.

This window should contain
glass from many restorations

spanning almost 800 years.

But they're finding only

original 13th century glass,

glass installed during
the 19th century

or panels containing both.

Where has all the
other glass gone?

We are finding lots of things

they altered quite strongly
the design of the panels,

the roses have been
extensively restored

and we have to...

study them again to understand
what has been done.

Karine and Elisabeth must work fast

while they still have this unprecedented
access to the south rose window.

They will continue their investigations
to try to solve this mystery.

Just above the south rose window

is one of 3 holes
in the vaulting

created as the
spire collapsed.

Incredibly the top section of
the spire survived the inferno.

Its slender pinnacle is
lodged in the vaulting stone.

The team gently nudges
this spire section free

and carefully winches it down.

We can still see
the structure

of how the spire
was made

with these fine
lead sheets

of a few
millimetres thick

that were used

on the entire structure
of the spire.

Six decorative lead roses

remain attached to the
spire's lead sheeting.

We will be able to study

how this decoration was made

touching the spire that was

just taken down
from the vaults today.

It's a magical moment.

The fire has given
scientists and historians

an opportunity to look deep
into the fabric of the structure.

Notre Dame pushed the limits
of Gothic architecture.

Advances in stone
construction techniques

such as the introduction
of flying buttresses,

allowed medieval masons
to build incredibly tall and thin.

As the team examines
the structure closely,

they discover metal hidden
throughout the cathedral

that could unlock more
of its architectural mysteries.

From the thousands of nails
that joined timber beams

to iron bars that brace
and hold secure

the stunning medieval
stained glass.

I was amazed that there's so
many iron in, in this building

that was never truly studied before.

The staples that we see here,

they're embedded in the...

maybe the oldest part
of Notre Dame's masonry.

These 45 centimetre long iron staples

secure the great arches beneath

and prevent the stone blocks from being
pulled apart by the enormous forces.

20 metres above,

along the very top of
Notre Dame's walls

the destruction of the roof

has revealed previously
concealed iron work

that may hold the secret to this
cathedral's gravity-defying height.

It's really exciting because
we're dealing with

unknown structures
on the top of the walls

that are so far unique
in Gothic architecture.

Medieval builders
may have been worried

that the top of Notre Dame's
tall slender walls

could be an Achilles heel.

The weight of the roof
could push the stones apart.

The destruction of
the roof has revealed

the builders tied
these stones together

with more than 500 staples,

creating a ring of iron,
holding the walls together.

This engineering master stroke

has remained hidden under the roof
of Notre Dame for hundreds of years.

The staples with
the flying buttresses

are two ways of preventing
the stones to collapse.

It's...

an ancient form, a form which
is known since antiquity

but it looks like in Notre Dame,

we're trying to use ancient
forms of reinforcement

such as the staple

in order to build a new
form of architecture,

really high, really thin,
Gothic structures

of which Notre Dame is
kind of the first true example.

Maxime uses
pioneering technology

to unlock the secrets
of the iron staples.

Like we're acting
as some kind of detectives,

trying to find out the digital prints,

the digital signature
of each of these staples

and try to rebuild their path

from the workshop
to the building site.

Radiocarbon dating confirms

they were installed
in the early 13th century

when this part of
the cathedral was built.

These are the oldest pieces
of iron used in a Gothic church

that we know of so far.

That's a huge discovery.

This is a revolution
in Gothic architecture.

No other Gothic monument
had used iron

in such a way
before Notre Dame.

Maxime reveals the
microstructure of the iron.

Multiple pieces of iron have been
forged together to form each staple.

The world is the result of
the mixing of scrap iron

to make a brand new iron staple.

We're maybe dealing with
the richest building site,

at that time,

and knowing that
it might have used almost

90 percent recycled iron,
opens new perspective.

The team has shown

that the recycling of iron

may have been commonplace
on the building site of Notre Dame.

Shedding new light on
medieval building practices.

The labs electron microscope

reveals further clues

to how far Notre Dame's
builders went to source the iron.

What we discovered is
that every single staple

has a different chemical signature.

All the staples,

they come from different iron
that was made in different places.

It means that there's
a truly active

iron market in Paris,

gathering iron from
many, many different origins.

These hidden iron staples

may also have played
a critical role

in the aftermath
of the fire of April 2019.

The staples were placed by the

medieval master mason

to reinforce the upper main walls,

they might have helped the walls

to prevent collapsing
during the fire.

To create the most advanced
church of its time,

builders of Notre Dame turned to
ancient construction techniques

only now fully understood
in the wake of the fire.

As a conservationist,

it's teaching us how

expert these builders were
in those days.

It's a testament to their

technical competence
and their vision

that they put in these
structural elements

which have preserved
the building for us.

Their knowledge might have
kept the cathedral standing

but the damage to the vaulting
reeked by the fire

is shocking to see.

For the restoration of Notre Dame,

it might just be the stone of the
vaults that's the biggest problem.

The thing is,
it got soaked with water,

firstly from the fire fighting

and then because the roof was missing
for months and the rain came in.

They've got a temporary roof up
now and it's starting to dry out

but even that has presented
an unforeseen problem.

As the stones dry,

salts are crystallising on the
underside of the vaulting

and they're breaking off
the outer layers of limestone.

All the damage
in this part

and on the-on the vault
is the result of the salt

you can see the
loss of material is

2 or 3 centimetres.

This is catastrophic for us.

In the 18th and 19th centuries

restorers cast sacrificial
layers of plaster

on top of the vaulting
in case of a fire.

This protected the stonework
from the heat of the 2019 inferno

but not from the water
used to fight it.

This, along with months of rain water

drew salt from the plaster
into the porous limestone.

As the moisture evaporates,
the salt crystallises

and forces the limestone apart,

destroying the inner
surface of the vaulting.

To find the solution,
you have to remove the salt.

- Remove the salt.
- As the salts are soluble salts,

you will have to use water...

- With water.
- ...and some other tricks.

To extract the salt,

the team will coat the vaulting
with a paste of clay, sand,

and purified water,
called a poultice.

The water from the poultice
is drawn into the stone

where it dissolves
the harmful salt crystals.

As the clay of the poultice dries,

it draws the salty water
out of the stone,

saving the vaulting
from further damage.

The poultices will be removed

when they will all have dried.

Workers chisel away the
mortar between the stones

to allow the poultice to
reach deep into the blocks.

Next, they load the sticky mixture
into a compressed air gun

and spray it into every crevice.

Finally, they carefully
smooth the poultice

across the face
of the vaulting stone.

You can see that it follows very, very
closely the surface of the stone

and what we recommend is that
poultice should not be thicker

than half a centimetre
to one centimetre,

otherwise there are risks
that it falls down.

So, do you have enough time?
You have to open the cathedral.

Can you have it there
as long as you need to?

If you wish,

all the poultices to be extracted,

we need to-to have
a very slow process

until the vaults are dry.

And this will take time,
much time,

so we have to get
the gusset ready

in 2024.

I understand those time constraints

because it's a worldwide
known symbol

and this building has to live again.

The poultice may stay in place

until the missing vaulting
has been rebuilt

and the cathedral is
permanently watertight.

It's the end of another
long day on site.

Notre Dame falls silent
once again.

Well, this is quite
a remarkable experience

because I've got
the deserted cathedral

to myself.

It's extraordinary.

And just over there I can still
see the remains of a burned

beam.

Which is a reminder

that amidst all the activity
that goes on in the daytime.

This is where the fire
actually started.

This is where nature
was out of control.

The medieval timber roof,
known as the forest,

was built section by section
over almost 100 years

as the cathedral grew beneath.

Hand axes were used to craft
each individual beam

for a specific position
in the roof structure.

The fire, which started in the forest

took just hours to reduce this
medieval masterpiece to ashes.

The team will soon begin
an unprecedented challenge

to rebuild the forest
in a matter of months.

Notre Dame's spire
is relatively modern,

built in the 19th century.

These beams were cut with saws,

so, it's down to the French sawmills

to transform 1,200 of the oaks

into flawless beams

with the precise dimensions
needed for the new spire.

Francois Feillet, runs this
sawmill in Normandy

that processes more than 30,000
tons of timber each year.

It's one of 45 sawmills
across France

that has answered the call to cut the
beams for Notre Dame's new roof.

The team wastes no time
in getting to work on the beams.

First stop, the debarker.

This machine excoriates the outer
layers, removing the loose bark.

Now, the 3-ton tree trunk
enters the cutting shed

and rolls onto the saw carriage.

The band saw blade
is a 1,000 pounds,

high speed, ribbon of steel

that runs at 43 metres per second.

This is a laser-guided,
precision operation.

Francois removes slices
just 3 centimetres thick,

to trim the beam down
to the exact dimensions

requested by the
Notre Dame architects.

The beams from Francois'
sawmill are stacked,

ready to join more
than a 1,000 others

coming from across France
for Notre Dame's new spire.

Inside Notre Dame,

the first chance in 160 years,

to get up close to the
vast south rose window,

has revealed a puzzle
the glass historians need to solve.

We should be finding glass
from all different periods.

We know the window's
been restored lots of times.

But the glass all
seems to be either

original 13th century glass or

relatively modern
19th century glass.

Where's the rest of it got?
It's a bit of a mystery.

The chief suspect
is architect, Violet Leduc.

In the 1840s,

he was tasked with breathing
new life into Notre Dame.

At the time, it was not the
beloved building we know today.

The cathedral was ransacked
during the French revolution.

Statues of kings on the
facade were decapitated

and it was used as a warehouse,

lying derelict and
unloved for decades.

Over 20 years,

Leduc reinstated the
statues of the facade,

he rebuilt the sacristy.

He designed hundreds
of new gargoyles

and he raised the ill-fated
65-metre tall spire,

a replica of the medieval original.

Violet Leduc, god bless him,

would have been what we consider
to be a starchitect, you know?

He was a man
who knew his mind,

he was a man who was highly
respected, really determined

and saw himself
as a powerful leader.

During his restoration,

Leduc removed all glass in the south
rose window that was not original

and replaced it with modern glass.

Elisabeth is also finding

that he made brutal changes to
some of the original glass panels.

What do you observe in this...

And he's lost his aureole, his halo.

I've come to the Paris media tech
of Architecture and Heritage.

These archives may
hold clues to why

Leduc made such dramatic changes
to the glass in the south rose window.

Ooh, what have you got here?

The spire. The spire.

- Have you seen this before?
- No, never.

So, I guess your colleagues,
the architects,

will be looking closely at this
to get clues for how it should be.

Oh, look. Is this Mr Leduc?

- No, I don't think.
- No?

I think it's monsieur Leduc,
he's put himself in the drawing.

The windows of the tribune...

- Look, look, look, it's the famous-
- Gargoyles.

it's the famous gargoyles.
Here they are.

Gargling.

What creature
do you think that is?

The gargoyles not only
frighten away evil demons

they also protect
Notre Dame's walls

by directing rain water
away from the cathedral.

That folder is a complete
treasure trove.

It's full of these really beautiful
drawings by Violet Leduc,

showing his plans for Notre Dame.

And it's such a treat to see them,

not only because they're beautiful

but because this folder contains
such important information about...

France's idea of itself,

that's captured in
Notre Dame cathedral.

But it's Leduc's plans for
the south rose window

that may hold the key
to unravelling its mysteries.

All this part here

- was destroyed in the 19th century.
- Yes.

They threw it away.

Violet Leduc recognised that it
was an original medieval design

but for him maybe it wasn't
the ideal 13th century rose

that's why he changed the design.

So he looked at
the medieval window

and he thought:
"No, that's not medieval enough."

Yes.

Yes, I think he said that.

But such radical changes
to the glass panels

suggest Leduc was motivated
by more than mere aesthetics.

After hours of research,

the team makes
a stunning breakthrough.

It sounds like you're
coming across

completely new
information. Is that fair?

In fact we just discovered that

there was a change
of structure of the rose,

there was an iron
reinforcement

in the centre of the rose,
but obviously it wasn't enough,

so Violet Leduc put it further
away from the centre.

When we moved
the iron work here,

I had to change the
form of the panels.

Leduc's vision for a more
medieval south rose

combined with the need to
beef up the iron reinforcement,

required him to change the glass.

But the historians find evidence

he actually altered the entire
stone structure of the window.

It's like two different windows.

In fact, he slightly...

turned the rose.

So, it's gone like this
and he's sort of gone--

Why did he do that?

That's a big change, isn't it?

Leduc's restoration was sweeping.

He removed a smaller
structural ring of iron

and replaced it
with a bigger ring

to strengthen the
core of the window.

He removed all trace
of previous restorations,

to replace them with
panels of new glass.

And he turned the whole
window through 15 degrees,

to make it
structurally stronger.

These two drawings in the archive
have been revelatory for me

because they've helped me
understand why Violet Leduc

may have messed with the
structure of the window.

This showed what
it was like before

and you see this vertical axis,
here we've got panes of glass,

that's not structurally very safe.

But after, in this drawing,
he's put in a big strong stone arm,

that's going to hold
the whole thing together.

I mean he wasn't just doing things
for aesthetic reasons,

he was also helping Notre Dame

to withstand the centuries.

Thanks to the scaffolding,

this team is painting
an intimate portrait

of how the south rose window,

one of the wonders
of this cathedral,

evolved to survive.

It's been such a privilege
to spend time

in this wounded

but wonderful cathedral

and it's clear how utterly dedicated

the architects, the restorers,
the scientists

are who've been tasked
with bringing it back to life.

I'll be amazed if they do
make their deadline of 2024.

But you know what?

There's no shortage
of ambition here.

This experience marks
another chapter

in my relationship with Notre Dame.
Oop.

A building that has inspired me
and countless others.

I've seen the vaulting secured,

the interior cleaned
of toxic lead dust,

and the mysteries
of its windows solved.

Next time, I'll be back to witness
the rebuilding of the vaulting,

the new roof,

and the spire under construction.

And maybe,

just maybe,

the reopening of this astonishing
building to the world once more.

And check out Lucy's Ladykillers
over on BBC sounds,

giving Victorian
women a voice

with a contemporary
crime twist.

And civil war makes
civil hands unclean,

dirty with inspiration,
Art That Made Us,

next here on BBC2.