♪ ♪ NARRATOR:
Notre-Dame de Paris. A treasured icon of Gothic
architecture and medieval construction. ELSIE OWUSU:
The level of determination and the feat of engineering
in those days, just extraordinary. NARRATOR:
But on April 15, 2019, disaster strikes. A huge fire rips through
the cathedral... (people exclaiming) NARRATOR:
...threatening to bring down
the entire structure. (revving) ♪ ♪ Now, master craftspeople
and engineers battle to bring Notre-Dame
back to life. PHILIPPE VILLENEUVE
(translated):
From what we've done so far, it's clear to us that this
cathedral will be extraordinary. NARRATOR:
Hundreds of workers are in an
ambitious race to restore this medieval
masterpiece in time for a grand reopening
planned for 2024. (speaking French): NARRATOR:
Historians and scientists
work together to analyze and reproduce Notre-Dame's
architectural mysteries. KARINE BOULANGER:
It is a very unique opportunity. It's a kind of a walking backwards in time. ♪ ♪ NARRATOR:
They're revealing ancient
technology hidden for centuries. MAXIME L'HÉRITIER:
We're dealing with
unknown structures that are, so far, unique
in Gothic architecture. NARRATOR:
And struggling to save the fragile structure of
the building. JEAN-DIDIER MERTZ:
The loss of matter is catastrophic for us. NARRATOR:
Now, three years into
this extraordinary five-year restoration project, can this team meet
its ambitious deadline? "Rebuilding Notre-Dame," right now, on "NOVA." ♪ ♪ ♪ ♪ NARRATOR:
Paris. A city of churches, basilicas, and almost 2,000 historic
monuments. On April 15, 2019, the 850-year-old Cathedral of Notre-Dame de Paris is
undergoing a six-and-a-half-million-dollar
renovation of the spire... ...when a fire breaks out inside
the oak framework of the roof. After 90 minutes, the 400-ton timber
and lead spire gives way and crashes through
the stone vaulting. The fire destroys the roof
and spire, and leaves three gaping holes in
the vaulting. The structure
is significantly weakened, and there's an urgent concern. If the remaining vaulting were
to fall, it could trigger a catastrophic
collapse. PASCAL PRUNET (translated):
We didn't know how the vaults,
the walls, the buttresses would behave in the absence
of the roof that had collapsed above. So, we had to stabilize the
structure. NARRATOR:
In the immediate aftermath, the focus is on protecting what has survived
from further damage. Engineers race to install supports beneath
Notre-Dame's flying buttresses to shore up the fragile
structure. Meanwhile,
water has saturated the vaults, adding weight
to the weakened stonework, increasing the chance of
a total collapse. And without the roof, the building remains open
to the elements. Before they can make
the structure watertight, workers have to remove 40,000 burned and melted
scaffolding poles left over
from the spire restoration. To keep the stonework dry, the team builds a wooden
platform. On top, a lightweight aluminum
frame covered with water-resistant
sheeting forms a temporary roof that opens and closes on a
system of rollers. PRUNET (translated):
It's an ingenious tool that
protects against humidity and shelters these vaults,
so they can dry. NARRATOR:
The rolling roof enables workers
to lower construction materials through
the central hole in the vaulting. During all this work, the medieval masterpiece has
been closed to worshippers and tourists
alike. WOMAN:
Pretty sad to see it like this. You can't get close to the
building at all. It's almost like you would
walk by it and not necessarily go to it as a destination,
like it once was. NARRATOR:
And what a destination it was. Around 13 million people
toured Notre-Dame each year before the fire. They came to marvel at a
building that pushed the limits
of Gothic architecture. WOMAN:
I was very connected to it. So I was quite broken after, you
know, hearing about the fire. NARRATOR:
We still don't know
how the fire started. But three years later, the ambitious project to restore
the cathedral has ramped up. MAN (speaking French): MAN 2 (on radio): (speaking French) ♪ ♪ NARRATOR:
The team here
has more than tripled in size. As many as 200 workers
are now battling to bring Notre-Dame back
to life. VILLENEUVE (translated):
We all really work with a lot of love and
gratitude, and we motivate each other
to meet the deadline and reopen the cathedral
to the public. NARRATOR:
The French Senate has ruled
Notre-Dame will be rebuilt exactly as it
was before the fire. Donors have contributed
almost $900 million towards this effort. But the task ahead is enormous. The team must remove tons of
toxic lead dust that remains of the old lead
roof left over from the fire, then clean and restore fragile
stained-glass windows. To reconstruct the roof
identically, they must fill the three gaping
holes in the stone vaulting, rebuild the timber framework
from almost 1,000 oak beams, cover it with thousands
of square feet of lead tiles, and raise the iconic
210-foot spire. It's the largest restoration
project in the cathedral's history. VILLENEUVE (translated):
I only have one goal-- repair
and rebuild the cathedral, put the rooster
on top of the spire, and say, "Mission accomplished." NARRATOR:
That's the plan. But before they can even start
work on this ambitious scheme, they must shore up
the remaining damaged roof. For hundreds of years,
the arched stone vaults, made from thousands
of cubic feet of interlocking
limestone blocks, supported the roof above. But now the vaulting is
extremely fragile. Repairing the arches
could trigger a collapse. To stabilize the structure, the team must install
52 timber support arches beneath the vaulting so they
can rebuild safely. ♪ ♪ But installing them more than
a hundred feet above the ground is no small feat. ♪ ♪ To do it, scaffolders have built
a giant steel structure inside to allow workers to access virtually every corner
of the immense cathedral. RÉGIS JAEGER:
It's a big job for our workers because it's a lot of material
and the access is difficult. We have 1,000 tons of scaffold. It's a lot of tubes,
big and heavy. It's a big, big challenge. OWUSU:
An extraordinary amount
of expertise has gone into creating
a skeleton to sit inside the building so that the outer building
can be rescued. NARRATOR:
It takes around 20 weeks
to build up the scaffolding inside the cathedral
in order to begin the installation
of wooden supports, shaped to match the geometry
of the vaults. YVES MACEL (translated):
This is where you need to be careful not to hit the
scaffolding or hit the vault. The challenge is to get
everything inside without damaging anything, without putting people in
danger. You have to be very, very
careful. NARRATOR:
Each temporary support arch
is fitted with metal brackets to secure it in place. Hydraulic jacks raise it to meet
the underside of the vaulting. MACEL (translated):
Each support is unique and has
its own specific location. (drill whirring) NARRATOR:
The arches connect to the rest
of the supporting framework. (translated):
If the stones were to move, they would come to rest on our
supports. Our supports will stay there
until the vaults are repaired. ♪ ♪ OWUSU:
It's almost as if you have
to design a building to keep the building safe. What you would normally define
as a temporary works has taken a level of ingenuity
and a level of skill which is quite exceptional. NARRATOR:
It takes six months to install
all 52 vaulting support arches. (translated):
The structure is no longer
at risk of collapsing after it was weakened by the
fire. NARRATOR:
Deputy director of operations
Jonathan Truillet helps coordinate the work
to bring Notre-Dame back from the brink. ♪ ♪ TRUILLET (translated):
It's a technical and
logistical challenge. And if we don't respect
our deadlines, we'll accumulate delays
and never catch up. NARRATOR:
The deadline of 2024
for completion isn't just a hopeful wish. This is when all eyes
will be on Paris for the Summer Olympics. A grand reopening of Notre-Dame will crown a year
of celebrations. TRUILLET (translated):
Everyone must mobilize to reach this objective. Even if it is ambitious,
it is achievable, if we have the drive to
accomplish it. ♪ ♪ NARRATOR:
Fewer than three years remain
to meet the deadline. With the vaulting to rebuild, the roof and spire missing, and the site still contaminated
by lead dust from the fire, the task is daunting. TRUILLET (translated):
We must work on multiple tasks
at the same time, have several worksites
within the worksite. We must intervene both inside,
to clean the site, and at the same time,
above our heads to rebuild the vaulting
and the roof. NARRATOR:
Above the stone vaulting, Notre-Dame's roof was completely
destroyed by the fire. Now one of the most complex
challenges is to entirely rebuild the thousand-ton timber
and lead roof. Chief architect Rémi Fromont
will oversee the reconstruction of the medieval roof structure,
known as the forest. FROMONT (translated):
We're going to participate in the reconstruction of this
absolutely emblematic, absolutely unique,
absolutely magnificent, and absolutely iconic work,
so it's very exciting. It was one of the first great
Gothic frameworks, extremely well-designed and ahead of its time,
from a technical point of view. NARRATOR:
During a research project
in 2014, Rémi and his colleague measured
the dimensions of every beam in the forest to create the first
comprehensive survey of Notre-Dame's roof. FROMONT (translated):
Our surveys were very useful. It's largely thanks to them that
we're able to restore the roof of the
cathedral identically. NARRATOR:
Rémi's team will need
850 oak trees to reproduce the Gothic roof
trusses. The cathedral's spire will be
built from another 1,200 trees. FROMONT (translated):
The spire is a huge task
to understand and restore. It's quite dizzying to think that we're building a
210-foot-high wooden structure perched 115 feet above the
ground on 13th-century masonry
destroyed by fire. We're not taking the easy way
out, really not. ♪ ♪ NARRATOR:
The spire was a 400-ton
engineering masterpiece. Hidden beneath the 16 copper
statues and over 100 tons of lead tiles was a complex skeleton of oak
beams, some as long as 65 feet. The secret of its strength? A dense lattice of oak tied
into the rest of the roof supports the entire structure. OWUSU:
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, quite
exceptional. NARRATOR:
Reconstructing this wooden
wonder to match the lost spire is no simple task. FROMONT (translated):
We'll rebuild identically, not because it's nice to build
in a 13th-century style, but because we need the new roof
to behave just like the old one. Do it differently and the structure will behave
differently. The timber that was used
originally was green, that's to say it was not dry. So we'll use green timber. NARRATOR:
In the 13th century,
hewing beams from hard, seasoned oak with simple hand tools
was arduous work. So carpenters cut their timber while it was still soft
and green. But building this way could be
risky. The medieval English town
of Chesterfield may bear 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. FROMONT (translated):
We need top-quality timber, perfectly straight, to avoid
this kind of problem. Working with green wood requires an extremely rigorous choice
of tree. NARRATOR:
In public and private forests
across France, the hunt for 2,000 perfect oaks
for Notre-Dame's roof and spire begins. One third of the country, 65,000 square miles,
is covered by forests. (translated):
We're going to choose
the trees. NARRATOR:
This crew of forestiers has their work cut out for them. They must source 60 flawless
oaks for the spire from an 8,000-acre forest. (translated):
We must inspect the tree
from all angles, otherwise you'll never know if
there is a defect. NARRATOR:
The oaks felled for Notre-Dame form part of France's annual
forest management quota. LOÏC EON (translated):
That way. But now we need to get
a bit closer, because something
is not quite right. There's damage 20 feet up,
so we can't choose this one. It won't meet the specifications
given for Notre-Dame's spire. So, we need to look for another
tree. MAN (speaking French): NARRATOR:
This oak was damaged as it grew. These twisted fibers make it too
weak for Notre-Dame's spire. But on the other side of the
clearing, another candidate emerges. EON (translated):
No damage, but we need to check the
diameter. We have a tree two feet in
diameter. AHMET CIRPAN (translated):
In terms of felling it,
there's no problem. (revving) NARRATOR:
Logger Ahmet Cirpan begins
by making a cut that will direct the tree to fall into the clearing. (translated):
It will go between those two
trees, here, in this direction. I don't cut with my chainsaw
at random. Okay, now we can start
the final cut. (saw buzzing) ♪ ♪ Yes, that's why we can't have
anyone getting in the way. NARRATOR:
Notre-Dame's medieval carpenters
used markings to help them reassemble the
beams 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 several months to complete the painstaking
search to source and fell their target of
60 trees. FROMONT (translated):
We're going to restore and
rebuild the missing parts, and that's something unique in
a career. We'll do it with all our heart,
passion, and above all, know-how. NARRATOR:
Oak will form the backbone
of the spire, but it will be wrapped in
a heavy metal-- lead. Although the spire was almost
completely incinerated, its pinnacle survived the
inferno. Lodged in the vaulting stone, the team gently nudges it
free... WORKERS
(speaking French): NARRATOR:
...and carefully winches it
down. L'HÉRITIER:
We can still see the structure of the spire was made, with this fine lead sheets
of a few millimeters thick that were used on the entire structure
of the spire. NARRATOR:
They find six decorative
lead roses attached to the spire section. 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. NARRATOR:
And there are more surprises
to come. Lead was decorative and kept
the cathedral watertight. But there's another metal
used here that allowed Notre-Dame's masons to push the limits
of Gothic stonework. ♪ ♪ Innovations such as flying
buttresses to hold up the thin outer walls allowed medieval masons to build incredibly high, without needing
massively thick walls. As the team examines the
structure closely, they discover metal
throughout the cathedral that could unlock more of its
architectural mysteries, from the nails
that join timber beams to iron bars that brace and hold secure the stunning
medieval stained glass. L'HÉRITIER:
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. NARRATOR:
These 18-inch-long iron
"staples" secure the great arches beneath and prevent the stone blocks
from collapsing under the enormous weight. 65 feet above, along the very
top of Notre-Dame's walls, the destruction of the roof has revealed previously
concealed ironwork that may have made
the structure's height and slender form possible. 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. NARRATOR:
Medieval builders may have
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 joined 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. L'HÉRITIER:
The staples, with the flying buttresses,
are two ways of preventing
the stones to, to collapse. It's an ancient form, a form
which is known since antiquity. ♪ ♪ NARRATOR:
Ancient engineers used
iron staples to lock the stones of giant
megastructures into place. These holes in the walls
of Rome's Colosseum were once filled with
iron staples that pinned the structure
together. But in medieval Paris, masons used this technology
to revolutionize architecture. L'HÉRITIER:
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. ♪ ♪ NARRATOR:
At his lab,
Maxime unlocks the secrets of each individual iron staple. L'HÉRITIER:
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 to try to rebuild their path from the workshop
to the building site. NARRATOR:
Radiocarbon dating
of organic material left over from
the smelting process confirms the staples 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 revolution
in Gothic architecture. No other Gothic monument had
used iron in such a way before Notre-Dame. NARRATOR:
Maxime examines the
microstructure of the iron. Each staple was produced by welding together multiple
pieces, suggesting that this iron
was recycled. L'HÉRITIER:
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 perspective. NARRATOR:
The research shows recycling
iron may have been common on the
building site of Notre-Dame, shedding new light
on medieval building practices. The lab's electron microscope
reveals further clues to the lengths that
Notre-Dame's builders went to in sourcing the material. L'HÉRITIER:
What we discovered is that every single staple has a
different chemical signature. All these 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. NARRATOR:
These hidden iron staples may
have also played a critical role in saving the building in the
wake of the fire. 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. OWUSU:
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. NARRATOR:
But Notre-Dame's marvels go beyond the walls and roof. The great cathedral's medieval
builders also pushed the limits of what
could be made with glass. The three rose windows date
from the 13th century, and together, they're made up
of over 1,100 panels. Protected by the stone vaulting, they survived the fire
unscathed. ♪ ♪ These kaleidoscopic wonders
are filled with depictions
of biblical scenes and saints. The scaffolding gives access
to these rose windows so experts can decode
their secrets. BOULANGER:
It is a very unique opportunity, because we won't see them again
in the same way, never. (in French): CLAUDINE LOISEL: NARRATOR:
Glass scientist Claudine Loisel and historians Karine Boulanger
and Elisabeth Pillet are working on the largest
window in Notre-Dame. The gigantic south rose window measures almost 42 feet
in diameter. They're busy mapping every shard
of glass. PILLET (translated):
It's a really big job. In fact,
I think at the beginning, when we looked at this
rose window, we had no idea of all the questions
it would raise. NARRATOR:
They hope to build
a complete picture of how the window has evolved
over centuries of restoration. The team must first identify
what is original 13th-century glass
and what is glass from subsequent restorations. BOULANGER (in French): (in English):
You see, there is a difference between this yellow
and this one. This one is more
translucent. It's 19th-century glass. This one is
13th-century glass. The difference in colors
results from the composition of the glass,
which was different between the medieval time
and 19th century. NARRATOR:
But there's a problem baked into the original
medieval glass: it's slowly decaying. LOISEL:
On the older glass, you observe much more
corrosion process in the glass composition. This glass composition was more
sensitive to the environment. NARRATOR:
In the 13th century, glassmakers used potash. Made from burnt wood and ferns
rich in potassium, potash reduced the melting point
of the ingredients used to make glass. By the 19th century,
sodium carbonate combined with calcium oxide was used instead,
and produced more stable glass that did not corrode. This factory on the banks
of the Loire River in France is one of the last places
in the world that can produce stained glass using medieval
mouth-blowing techniques. SIMON BALLAGH:
We produce glass for
major historical buildings as Versailles
or the White House. NARRATOR:
The team starts
by mixing sand, metal oxide for color, sodium carbonate, and calcium. They heat the mixture to over
2,000 degrees Fahrenheit and build up layers
of the molten glass on the end of a blowpipe. The glassblower forms
a sphere from the red-hot mass, rolling 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 glassblowers
uses their sense, their feeling, to blow one glass sheet. HERVÉ GRIMAL (translated):
Glass is a living material. It takes a long time to get to know it,
to feel the material at your fingertips. NARRATOR:
The glassblowers enlist
the help of gravity. They swing the 15-pound ball of
glass in a 13-foot-deep pit to elongate the ball
into a tube. GRIMAL (translated):
It's a profession where there's weight
and there's heat. So you have to be strong,
tough at times. It's a very demanding job. ♪ ♪ NARRATOR:
Hervé has blown glass here
for more than 33 years. GRIMAL (translated):
For us, it's about always having
the right length, the right diameter, and the right thickness of the
glass, too. NARRATOR:
Once the cylinder has cooled,
they make a single cut... ...and send it to a special
furnace, where it's unrolled. Extreme heat of nearly
1,400 degrees Fahrenheit and a wood block
smooth out the glass and minimize imperfections. GRIMAL (translated):
The goal is to try to get
a very even thickness, to achieve the perfect sheet. NARRATOR:
They carefully inspect each pane
and remove any rough edges. BALLAGH:
Every glass sheet is different,
and it has the spirit of the glassblower. Losing this patrimoine and
know-how would be a disaster. ♪ ♪ NARRATOR:
The factory marries
these techniques with the latest technology to accurately reproduce
stained glass. BALLAGH:
We can fit perfectly with the old colors 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. GRIMAL (translated):
We'll be making glass for the restoration
of Notre-Dame in Paris, which will be
a high point in my career. Well, it will make
for a nice resumé! NARRATOR:
The team's knowledge
of historic techniques, combined with modern technology,
enables them to reproduce any of Notre-Dame's
stained glass from any century. BOULANGER:
A stained-glass window is always a mixture
of original glass and restoration from
every century, almost. Until the 20th century, when a glass was
too badly damaged, we had to replace it. NARRATOR:
While mapping
the south rose window, they uncover an unusual trend. They expect to see glass
from multiple restorations spanning eight centuries. But they're finding original
13th-century glass, glass installed during
the 19th century, with some panels
containing both. BOULANGER:
We are finding lots of things. They altered quite strongly the design of the panels. NARRATOR:
While the glass team has this unprecedented access,
they must work fast to solve the mystery of why
the south rose window only has 13th-
and 19th-century glass. ♪ ♪ The clock is ticking for
the architects and restorers. To meet the challenge of
reopening Notre-Dame in 2024, the workforce here
has increased dramatically. Up to 200 people pass through
the site each day. ♪ ♪ But the lead dust that coats every surface
makes operating here potentially dangerous. Protective clothing
is essential. Blaise Gomis is part of a team
dedicated to safeguarding workers
from the deadly effects of lead poisoning. Without them, this huge
operation would grind to a halt. GOMIS (translated):
Between the polluted zone
and the clean zone, there's us. You have to go through us. We take names so we have a count
of the people on site. Then, after they finish
their job, when they leave,
they must go past me again. (in French): WOMAN: GOMIS: WOMAN: GOMIS (translated):
Lead, as you know, is harmful. So they must be equipped. We give them overalls, underwear, boots, and helmets. (suit zipping) ♪ ♪ And when they leave,
they take showers to make sure they eliminate as much lead
as possible. NARRATOR:
To make the site safe,
the team's next challenge is to remove all the
toxic lead dust. They tackle the
cleaning zone by zone, eventually decontaminating
the entire cathedral. But this operation kicks dust
into the air. (vacuum whirring) Workers in an area being cleaned must wear heavy-duty
breathing equipment. Clara Dupuydauby is one of 40
decontamination experts that use special vacuums
to meticulously clean every inch of Notre-Dame's vaulting, walls, pillars, and floors. With this equipment, we only work two hours
and a half at a time, and we need to stop
to take a break. We go have lunch. And two hours and a half,
and we go home. NARRATOR:
Vacuuming the lead dust
will take eight months. Then restorers can move on
to deep-clean the stone for the first time
in its history. Inside Notre-Dame, it's already possible
to get a sense of how dramatically changed
the cathedral will be after the cleaning. Beneath the lead
and centuries of smoke from millions of candles
lies gleaming limestone. This is how the cathedral looked
850 years ago and will again soon. VILLENEUVE (translated):
Here are the stages. PRUNET (translated):
First step, second step... Dirty, intermediate,
and final. That's great. (drill whirring) NARRATOR:
The restorers working at
Notre-Dame are among France's foremost
experts in their fields. ♪ ♪ Guiding this impressive
concentration of medieval knowledge are chief architects
Pascal Prunet and Philippe Villeneuve. VILLENEUVE (speaking French): (translated):
Let's go and meet
the cleaning team. (translated):
The stone's changing color. We're very satisfied with that. But we know this is only
the first stage of the cleaning. (translated):
But after, we'll be able
to work without masks, so that's the goal. VILLENEUVE (translated):
When we look at this vaulting,
it's clear to us that this cathedral will be extraordinary. So it's all enormously
energizing. NARRATOR:
But this team still has
a big job ahead if they want to reopen
the cathedral in 2024. VILLENEUVE (translated):
It's a completely crazy
deadline. But despite everything,
we continue to work so it can be met. ♪ ♪ NARRATOR:
To meet the deadline, the team cannot afford
any unexpected delays. But an insidious threat
to Notre-Dame's stonework is developing. With the loss of the roof
and no protection from the elements for almost two
years after the fire, the exposed stone vaulting
was repeatedly soaked by rain. ♪ ♪ Now protected by the
temporary roof, it's drying out. But as the stones dry, salts are crystallizing on the
underside of the vaulting, breaking off the outer layers
of limestone. All the damage in this part
and on the, on the vault is a result of the salt. You can see the loss of matter
is two or three centimeters. This is catastrophic for us. NARRATOR:
In the 18th and 19th centuries, restorers cast 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, washed salt from the plaster
into the lower layers of the porous limestone. As the moisture evaporates,
the salt crystalizes, and forces the limestone apart, destroying the inner surface
of the vaulting. We don't have the original
surface of the, of the stone. It is a real problem from
an historical point of view. NARRATOR:
Geologist Véronique
Vergès-Belmin will use a technique to draw
the salt out from the stone. We need to use a material
that can absorb the salt and extract them through
capillary forces. NARRATOR:
To extract the salt,
Véronique's crew will coat the vaulting with a paste of
clay, sand, and purified water known as 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 salt water
out of the stone, saving the vaulting
from further damage. The poultices will be removed
when they will all have dried. (tool whirring) NARRATOR:
The restorers chisel away
the outer layer of mortar between the stones to allow
the poultice better penetration. (machinery running) 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 areas affected by the salt damage. VERGÈS-BELMIN:
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 centimeter
to one centimeter. Otherwise, there are risk
that it falls down. We need to have
a very slow process until the vaults are dry. But this will take time,
much time. We have to get the cathedral
ready in 2024. This building has to live again. NARRATOR:
The poultice may stay in place
until the new roof is built and the vaulting is permanently
protected from rain and snow. Notre-Dame was built over the
course of a hundred years, section by section, during the 12th and 13th
centuries. As each new segment of the
cathedral was constructed, another section of timber roof,
known as the forest, was built to cover it. Hand axes were used to craft
each individual beam in the medieval 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 under two years. FROMONT (translated):
We're going to reuse techniques that are extremely similar
to what was used, because it's technically
necessary, and if we don't do that, the
wood will behave differently. NARRATOR:
The spire lost in the fire
was erected in the 19th century. These beams were cut with saws. So today, Rémi's carpenters
will use modern saws to cut the new spire beams. FROMONT (translated):
We have extremely rigorous rules
that are the highest that can be had in carpentry, because Notre-Dame
is absolutely exceptional in terms of wood quality. NARRATOR:
This sawmill in Normandy
processes over a million cubic feet of timber
each year. It's one of 45 sawmills
across France that has answered the call to cut beams
for Notre-Dame's spire. (translated):
For us, it's a chance
to prove our dynamism and show that French forests can
help rebuild this structure-- one of the jewels of France. I do this as a form of
philanthropy-- it's for free. NARRATOR:
The team wastes no time in getting to work on the beams. First stop: the debarker. ♪ ♪ This machine strips off
the outer layers, removing the loose bark. Now the one-ton tree trunk
enters the sawmill and rolls onto the saw carriage. FEILLET (translated):
On this joystick, we have buttons that allow you
to do operations like log loading or what is
called slabber chipping. The slabber is the first machine
before the blade, which shreds away
the outer part of the log. NARRATOR:
The bandsaw blade is a high-speed loop of steel
that runs at 140 feet per second. François removes inch-thick
slices to trim the beam down to the dimensions requested by the Notre-Dame architects. ♪ ♪ FEILLET (translated):
What I enjoy most
is discovering the wood. Each tree is unique. Ultimately,
it's a game of strategy you play with each tree. It's never the same thing--
it's something new every time. ♪ ♪ NARRATOR:
The beams from François's
sawmill are stacked, ready to join more than
a thousand others coming from across France
for Notre-Dame's new spire. (translated):
A sawmill like ours,
we will not do anything like this again in our lives. We'll go down in history for
having modestly contributed, like everyone working on
Notre-Dame, to restore this cathedral--
our cathedral. ♪ ♪ NARRATOR:
Inside Notre-Dame,
the first chance to get up close to the gigantic
south rose window in 160 years... (speaking French): NARRATOR:
...has revealed a mystery. We only have 13th-century glass
and 19th-century glass. In the 19th century, they removed everything
that wasn't 13th century, and then they had to do
new panels if a panel was missing. ♪ ♪ NARRATOR:
The chief suspect for these
radical changes to the window is architect
Eugène 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 biblical kings on the
façade were decapitated, and it was used as a warehouse, sitting derelict and unloved
for decades. Over the course of 20 years, le-Duc reinstated the statues
of the façade, rebuilt the sacristy, designed hundreds of
new gargoyles, and raised the 210-foot spire. OWUSU:
Viollet-le-Duc, 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. NARRATOR:
And he used his power to make
some puzzling changes. 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
significant alterations to some of the original glass panels. (translated):
Look at this little martyr-- it looks like she was cut. She's missing the colored lines
around the edge. The halo is slightly cut here,
and her feet are cut, too. Maybe she has been moved
within this window. (speaking French) NARRATOR:
Why did le-Duc alter the window? Was he trying to impose
his own design? ♪ ♪ The glass experts hunt for clues here, at the Paris Médiathèque
of Architecture and Heritage. They hope le-Duc's plans for the south rose window
shed light on his thinking. BOULANGER (speaking French): NARRATOR:
As they dig into the archives,
they make a breakthrough. BOULANGER:
We just discovered that there
was a change of structure. Before Viollet-le-Duc,
there was an iron reinforcement in the center of the rose,
but obviously it wasn't enough. So Viollet-le-Duc put it
further away from the center. And when you removed
the ironwork here, he had to change the form
of the panels. NARRATOR:
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 traces of
previous restorations to replace them with panels
of new glass. And he rotated the whole window
15 degrees to make it structurally
stronger. The problem must have been
that the medieval rose wasn't stable
in its axis. That must have been the problem. That's very interesting. ♪ ♪ NARRATOR:
Le-Duc's major changes
to the south rose were motivated by more than mere
aesthetics. Strengthening the window
has helped preserve this masterpiece. We don't come across this kind
of new information every day. ♪ ♪ NARRATOR:
Thanks to the scaffolding, these historians and scientists are painting an
intimate portrait of how the south rose window, one of the wonders
of this cathedral, evolved to survive. ♪ ♪ Three years into the ambitious five-year restoration project, the team at Notre-Dame
has already stabilized the structure, the process to free
the cathedral from the toxic lead is underway, and two "test chapels"
have been fully restored. MARIE PARANT (translated):
We are very surprised by the
quality of the materials. They used beautiful pigments, gold of very good quality--
a very beautiful technique. NARRATOR:
Here, mural painting and
stonework restoration techniques have been tested. They will be replicated
throughout the rest of the building. PARANT (translated):
In the long term, it's to optimize the restoration
of all the other chapels. We're very happy. We feel that we've played
our part. It's really the first step towards the complete restoration
of Notre-Dame. ♪ ♪ NARRATOR:
But there's still
a long way to go. Rebuilding the vaulting,
the roof, and the spire identically
will be a monumental task. (translated):
It's extremely ambitious work,
considering the schedule. (translated):
We have a huge responsibility to the generations of today
and the future. ♪ ♪ NARRATOR:
Meanwhile, historians
and scientists are rewriting our understanding of the very fabric
of this medieval wonder. ♪ ♪ It opens new perspective. That's a huge opportunity. OWUSU:
Tragic as the fire was, I think it took something
like that to make us understand just what an absolutely amazing
work of collaborative genius that building was. WOMAN:
Notre-Dame is Notre-Dame. (chuckling):
We definitely need it back. ♪ ♪ NARRATOR:
The last chapter
of this extraordinary endeavor has begun: to return Notre-Dame
to France and the world. ♪ ♪ ♪ ♪ ANNOUNCER:
To order this program on DVD,
visit ShopPBS. Or call 1-800-PLAY-PBS. Episodes of "NOVA"
are available with Passport. "NOVA" is also available
on Amazon Prime Video. ♪ ♪ ♪ ♪
