All language subtitles for Rebuilding Notre-Dame.s01e02.The Next Chapter

Notre-Dame de Paris.

A treasured icon of Gothic
architecture

and medieval construction.

- The feat of engineering, in those
days - just extraordinary.

- It's one of the most important
monuments in France.

- But on the 15th of April 2019,
disaster strikes.

A huge fire rips through the
cathedral...

- Oh!

- Oh, no!

- ..reducing the roof and spire to
ashes.

For the last three years...

..our cameras have been following

teams of master craftspeople and
engineers,

as they battle 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.
- 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 matter is catastrophic
for us.

- Three years into this extraordinary
five-year restoration project...

..this is the next chapter in the race
to save Notre-Dame Cathedral.

Paris.

A city of churches, basilicas,

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
restoration of its spire.

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

After 90 minutes,

the 360-tonne 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 burned 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 Historic Royal
Palaces.

I first came here aged 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 three 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.

IN FRENCH:

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's 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
towards this effort.

But the task ahead is enormous.

The team must remove tonnes 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 three gaping
holes in the stone vaulting

and rebuild the timber framework from
almost 1,000 oaks 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...

- OK.

- ..to pass into "the dirty zone".

The way on to 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! SHE
CHUCKLES

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

There's a lift going up into the nave.
My goodness.

A lift made out of scaffolding.

Ah, bonjour, Jonathan.
- Bonjour.
- 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 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 1.5-tonne
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.

Ah!

That was a mistake, to look down.

Oh, look, here's the window. We at the
level of the windows.

Wow.

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

The glass is so...

..rich.

So intense.

Ooh!

- Bonjour.
- Bonjour.
- Bonjour.

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 just
astronomical. It's incredible.

I notice 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,

cos 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 decreed that the
landmark

must be rebuilt within five 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.

So this is to keep you safe? It cleans
the air?
- Yeah.
- Yeah.

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

- It goes there, in my vacuum.

- Oh, into the... Into the backpack?
- Yeah.
- Yeah.

- With this equipment, we only work
2.5 hours at a time...

..and we need to stop take a break.

- How long will it take to clean the
whole cathedral?

- There are different phases of
cleaning.
- Yeah?

- Now we're in the first one.

- Only the first phase? More cleaning
to come?

- Oh, yeah, yeah.
- Oh, my goodness.
- It's only the very beginning.

- The vacuuming of the lead dust will
take eight months.

Then 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!
- Yeah.

- I think you deserve a cup of coffee
now.

- Well, I've already had three cups of
coffee today!

- THEY LAUGH

Go enjoy your break.
- Thanks.
- You deserve it.
- Yeah.

Bye, Lucy.
- Ta-ra!

You know, it's obviously tragic that
the cathedral burnt,

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 millions
of candles,

lies pristine limestone.

This is how the cathedral looked 850
ago, and will again soon.

As the cleaning progresses,
craftspeople 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...

..they're 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-tonne
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.

Remi's team will need 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-tonne engineering
masterpiece.

Hidden beneath 16 copper statues and
140 tonnes of lead sheeting

was 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.

It's thought the 660-year-old crooked
spire of 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 forest.

This team of forestiers 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 wide enough and tall
enough to form a spire beam.

Lumberjack Ahmet Cirpan begins by
making a cut

that will direct the tree to fall into
the clearing.

CHAINSAW WHIRS

Notre-Dame's medieval carpenters

etched Roman numerals on their beams

to reassemble them correctly up on the
roof.

Today, this team attaches a barcode

to each oak destined for the
cathedral,

so they can track it from the forest

to its final position in the new
spire.

It takes 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

circle 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 won'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 three 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 Margaret.

She's tamed the dragon.
- She's tamed the dragon?
- Yes.

- Oh, I can see, she's telling it,
"Down, dragon, down!"

That's fabulous, I love it.

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

This is your superpower.
- Yes, in a way.

It's 13th-century glass but there are
some restorations, of course.

You see, the colour of the glass is
different.

- So I'm guessing that...

that bit there, 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 not medieval?

- 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 evolves. A 13th-century
painter won't paint the same way

as a 15th-century painter, obviously.

It's 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 the 13th
century you used potash

and it causes corrosion.

- That's potash over eight 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 manual know-how.

There is absolutely no machines

and the glass-blowers use their sense,
their feeling

to blow one glass sheet.

- The team enlist the help of gravity.

They swing the seven-kilo ball of
glass in a four-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 it 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 glass
was too badly damaged,

they had to replace it.

There were 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 are possibly 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 three 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 is so many
iron in this building,

that was never truly studied before.

The staples that we see here,

they're embedded in 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
ironwork 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 masterstroke 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.

- 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 weld 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% recycled iron

opens new perspectives.

- 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 lab's 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 an
ancient construction technique,

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 wreaked
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 firefighting,

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 vault is the result of the salt.

You can see the loss of matter is two
or three cm.

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 rainwater,

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?
- And as the salts are soluble salts,

you will have to you to use water....
- Use 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.

- And you can see that it follows

very, very closely the surface of the
stone.

And what we recommend is that the
poultice should not be thicker

than half a centimetre to one
centimetre,

otherwise there is a risk that it
falls down.

- 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 salts to be
extracted,

we need to have a very slow process
until the vaults are dry.

And this will take time, much time.

So we have to get the cathedral 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.

SPEAKS IN FRENCH

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.

IN FRENCH:

Francois Feillet runs this sawmill in
Normandy

that processes more than 30,000 tonnes
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 three-tonne tree trunk enters
the cutting shed

and rolls on to the saw carriage.

The band saw blade is a 1,000 lb
high-speed ribbon of steel

that runs at 43 metres per second.

This is a laser-guided precision
operation.

Francois removes slices, just 3cm
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 1,000 others,

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

IN FRENCH:

- Simplement.

- 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 gone? It's a
bit of a mystery.

The chief suspect is architect
Viollet-le-Duc.

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,

Le-Duc reinstated the statues of the
facade -

he rebuilt the sacristy,

he designed hundreds of new gargoyles

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

a replica of the medieval original.

- Viollet-le-Duc, God bless him,

would have been what we consider to be
a star-chitect, 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,

Le-Duc 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 one,
Elisabeth?

ELISABETH CHUCKLES

IN FRENCH:

He's lost his toes! His toes...
ELIZABETH CHUCKLES

And part of his dress and he's lost
his aureole, his halo.

- Absolument.

- IN FRENCH:

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

These archives may hold clues

to why Le-Duc made such dramatic
changes to the glass

in the South Rose Window.

Ooh, what have you got here?

Oh, wow!

Oh!
- 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 Monsieur Le-Duc?

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

I think it's Monsieur Le-Duc, he's put
himself in the drawing.

THEY ALL CHUCKLE

- The windows of the tribune...

And the higher windows.

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

- It's the famous gargoyles. Here they
are!

Gargling, hee-hee.

What creature do you think that is?

The gargoyles not only frighten away
evil demons,

they also protect Notre-Dame's walls
by directing rainwater

away from the cathedral.

That folder is a complete treasure
trove -

it's full of these really beautiful
drawings

by Viollet-le-Duc,

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 Le-Duc's plans for

the South Rose Window that may hold
the key

to unravelling its mysteries.

All this part here was destroyed...
- Yes.
- ..in the 19th century.
- Yes.

- They threw it away.

- Viollet-le-Duc 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 a medieval window
and he thought,

"No, that's not medieval enough"?

SHE CHUCKLES
- Yes. In his point of view, yes.

I think it was that.

- But such radical changes to the
glass panels

suggest Le-Duc 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 Viollet-le-Duc put it further away
from the centre.

When he removed the ironwork here, he
had to change some of the panels.

- Le-Duc'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 FRENCH:

- In fact, he slightly...turned the
rose...

- Ah... So it's gone like this

and he's sort of gone,
"E-e-e-r-r-r...".

CHUCKLING

So, why did he do that? That's a big
change, isn't it?

Le-Duc'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 Viollet-le-Duc 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 has 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 do 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.