The renaissance of Notre-Dame Cathedral: Behind the scenes of a monumental restoration • FRANCE 24

It was both a marathon and a sprint. An intricate puzzle and the greatest of all challenges. For four years now we've taken you on a journey around France's most closely scrutinized construction site, between tradition and modernity. Technology fit for the 2020s combined with traditional techniques, a jewel of the Middle Ages whose fate was entrusted to thousands of men and women across France. A monument restored identically to the cathedral designed in 1844. We're inviting you to join us one last time, taking you behind the scenes of what the whole world will remember as the building site of the century. Let's go back to the start. It's the 15th of April 2019, a little before 8pm. The spire of Notre Dame has just been engulfed in flames to the horrified cries of witnesses. An image that would travel the world. The cathedral spire collapsed into the building. A part that stood here for 800 years. Four and a half years later it took months to erect a 600-tonne scaffold so the spire could be rebuilt. With a year to go before it was due to reopen, the new cockerel statue that was to tower above it was blessed by the Archbishop of Paris. This gilded copper statue was designed by the chief architect. This cockerel has the virtue of being a memorial, a reminder, 100 metres above the ground. So it's not something that's very visible from here. But when it's up there, people will realise that it's not that big. But it's important that this cockerel means that something happened on the 15th of April and that the cathedral rose from the ashes. Placed inside the statue alongside three relics, a sealed cylinder containing a list of names. Those of the 2,000 specialist artisans who took part in the whole project. With its wings in the shape of flames, the statue resembles a phoenix as it's hoisted to its place on top of the spire. A symbolic reward under the golden skies of Paris. The animal representing those who wait for the coming of a new dawn. In February 2024, the gradual dismantling of this forest made of metal finally revealed the spire and its ornament. Restoring the cathedral's historic silhouette. Standing tall at 96 metres above the ground, this spire once again marks ground zero, the starting point for all of France's roads. 300 kilometres away in Ville-du-Les-Puels, northwest France, we'll have access to some of Notre-Dame's central elements. Without which the cathedral would lose a vital part of its identity. So here we are in the workshop of the Corny Harvard Bell Foundry. This is the workshop in Normandy where we made the bells for Notre-Dame in Paris in 2012. Damaged by the fire, these giant instruments have returned to where they were created 12 years ago, the 850th anniversary of the cathedral. The first step was to assess the damage to the eight bells in the north belfry. We started by doing an acoustic analysis. We weighed the bells to check that the weight, note, sizing and qualitative elements hadn't been altered since 2012, and that was the case. We had a few doubts about two of the bells, so we carried out a heat treatment and welding on one of them to restore its original integrity. The integrity of a bell is mainly determined by how it rings. It needs to be examined to ensure the heat hasn't affected its note. This is Marcel. She's 12 years old and weighs almost 2,000 kilos. It may not seem like it, but at this level of precision, the ear alone cannot do the job. A very good musician will perceive a difference of ten hundredths of a semitone. Here, we're at one hundredth of a semitone. All the ringing we did in 2012 was based on the historic note of Immanuel, which sounds an F sharp in the second octave at minus 55, 100 pitch 440. And all the new bells have been designed to ring with Immanuel in perfect harmony, whether in terms of sound power or whether in terms of notes. Another major challenge is the size and weight of the eight bells. We're in a relatively small city centre workshop in terms of space, so we had to create a system to secure the bells, store them and keep them safe as the restoration work progressed. Two young designers were chosen to create the rack based on two criteria, to reflect the aesthetics of the site, as well as to support 17 tons of bell. The biggest, Gabriel, weighs just over 4.1 tons and the smallest, Jean-Marie, is 800 kilos. Each bell bears this tribute to Saint Augustine. The route that seeks out travellers. It is for those travellers that the bells will ring again. In the meantime, we're back in the capital at the top of the construction site where a crucial stage is about to be completed. An unobstructed view over the roofs of Paris, enjoyed by Philippe Jost, who was taken over from General Georges La as head of the construction site. We don't want to be in competition with what you've done. We know it's symbolic, but it's a symbol to which we're personally attached. I suggest, Your Grace, that you place the first peg. Very well. This formalized gesture marks the end of the restoration of Notre-Dame's roof structure. It's identical to the one nicknamed the forest that burned in 2019. It's going wonderfully. Olivier, it's like you've been doing this all your life. My dear Philippe, I don't think so. This is a very important step from every point of view, symbolically speaking. It's also a very fine piece of work, finished by hand to an extraordinary standard. The skills being deployed on this site are truly fabulous. They are a credit to France. At the same time, we have a nice moment, a traditional moment for carpenters. The bouquet. In this Notre-Dame spirit, you can hear the cheers. It's a very beautiful moment. To celebrate the end, more than 40 carpenters and framers adorn the fruits of their labor with the traditional final bouquet. Less than a year to go before the building reopens, these craftspeople are saying goodbye to the site, a moment of pride and emotion. It's a young team. Yes, it's a very young team. We're both 30 years old, but we are part of a team that was there more or less from the start, so we've been able to follow the development of the site. Obviously, a year on, you can't help but be impressed. We have butterflies, as you might say. Magic has been done here. It's something that will stay with you all your life, will remember for the rest of our lives. There's a lot of humanity in these structures, and that's why they're so beautiful. It's because there are so many people. The more human there is, the more beautiful it is. It's got soul. There's soul and meaning. Soul and meaning. A phrase that the Gargas artisans wouldn't argue against. We have another meeting in this Provence commune, this time 700 kilometers away from ground zero. The Mathieu Chandelier factory took up residence here in 2002 in these former ochre factories. But the company, handed down from generation to generation, was first set up after the Second World War. Regis Mathieu took over from his mother at 19 years old. And his daughter, Ines, joined the family business two years ago. The fact that I started out with Notre-Dame is a source of great pride, and I'm pleased it marks the future succession of the company. Awarded the Living Heritage label, the workshop has been maintaining the cathedral's candelabras and chandeliers, as well as restoring original Notre-Dame architect Viollet-le-Duc's great crown of light, which was moved to the Basilica of Saint-Denis in 2014. Ten years later, despite the experience gained, there's still many challenges to overcome in the wake of the fire. There were some lights that had fallen down, they were completely destroyed, or in any case, half the chandelier was completely twisted or dented. We had to recreate some pieces because they disappeared over time. It's all about a dozen skills around the industry. There are craftspeople who spend about two months per chandelier restoring them. My name's Gregory, I'm a bronze fitter. I'm Mathilde, and I'm an electrical fitter. I'm Michael, I'm an electroplater, and I do the patinas. I'm Maxence, site manager and responsible for light fittings. My name is Jean de Dieu, I'm a polisher. The hundred or so pieces entrusted to the chandelier experts are first de-polished, the lead is removed, and then they pass into the hands of Jean de Dieu. Can you see the varnish? We're going to strip it off with this solvent. The start of a long process. There were 16 arms per chandelier. 16 arms for 13 chandeliers, each taking roughly 30 minutes. That's 104 hours of work, or more than four days, just for this one step. But after stripping, then cleaning, comes the polishing. Jean de Dieu's speciality. That's the miracle. With Notre-Dame, there are always miracles. But the miracle would not be complete without the final stage, the varnishing. And here again, the supernatural is called into play. Mr Mathieu calls me the magician. I took a light fitting that was in fairly good condition to get my colour reference. It took more than 50 tries to get this result. That's the original colour you can see there. You can't tell the difference from the original colour. It's on purpose. When you see the chandeliers upstairs, you're happy. You think, that's our work. People walk past it and they don't even realise that's the fun of it. That's rewarding for us. Are you looking forward to seeing the result? Oh yes, I'm definitely going there. A cathedral without its lights is so sad. You don't get that aspect, that luster that makes you look up. That's what makes us look at the whole cathedral. It's what makes the walls shine, the paintings shine. It's what brings it to life. The chandeliers will soon be returning to the central nave of Notre Dame, giving it back what had been lost in the fire. A little bit of soul. But before the doors open again, the cathedral will also have a moment to catch its breath. We enter just after the workers have left. Under the eye of the West Rose, the great organ resounds once again as the construction hammers finally fall silent. It's 9.57, almost 10pm. Apart from the organ fan and a few little noises coming from the organ itself, you can't hear anything in the cathedral. It's really a great silence and a great privilege to have a quality of silence like that. Because even once the cathedral has been given back to worship, to the faithful, to tourists, obviously we'll never have this quality of silence again. Bertrand Catiot has spent more than half a century at the service of Notre Dame's lungs. 52 years ago, almost to the day, I came to this gallery to meet Jean-Loup Boisseau, who was an organ builder. I was 17 and I fell in love with the cathedral. And its great organ, astonishingly safe from the fire. Neither the flames nor water from the fire brigade harmed it. However, it was contaminated by lead and had to be completely dismantled to be cleaned up. So it has to be tuned again. Laurent will be at the keys and he'll listen very carefully to each note. And he'll be able to say, for example, that this one is perhaps a little louder than the other. So we need to reduce the sound intensity of this pipe. And to work the pipes, you have to get 13 meters above the keyboard. It has to be earned, but a few hundred steps above lies the reward. Tuning an organ means giving it the right notes and ensuring that all the notes sound just right. Does it sound right? It sounds just right. When it doesn't, the offending pipe or pipes have to be lengthened or narrowed. A job done by hand. There's a natural phenomenon whereby two pipes of the same note that aren't completely in tune produce a beat. So it goes woo, woo, woo. And the aim is to remove this beating sound. With this tool, I can raise the pitch by doing this. It opens the pipe. Or I can mold it, tap on it, and the metal bends. You have to do that on every pipe on the organ. There are 8,600 or so. Nearly 8,000, in fact. But they have to be checked several times, which means six months' work. A small price to pay to restore the powerful sound of the largest organ in France. With less than four months to go before the church reopens, we make a final visit to Notre-Dame, where we meet with Marcel, Gabrielle and Anne Geneviève. The eight bells are to be blessed before returning to the north belfry built by the carpenters. What's important today is that the cathedral is a sign. A sign that peace is possible. A sign that everyone is welcome, whoever they are. Whether they are believers or non-believers. Notre-Dame is Notre-Dame de Paris. A cathedral for Catholics, but also a cathedral for Parisians. It's also the Notre-Dame of humanity. It is, in a way, the world's cathedral. And I know that all over the world, millions of people want to be able to come back here in the coming months because they were so upset when the fire broke out. The cathedral in the sky, which fell silent in 2019, will once again ring out. In the meantime, the bells have returned home. Marcel, who we filmed in April, was dragged by workers centimetre by painstaking centimetre to the top of the north belfry. The gaping wound in the transept crossing where the spire pierced the vault in 2019 has been closed. We're only going to do this once in our lives and at the end of the work, I think we'll be proud of what we've done. Right under Fabien's feet, the four angels of the resculpted and redecorated Oculus once again watch over the cathedral. Chapel restorer Mary Baron is taking stock. The human side is exceptional. You really get to understand each other's professions. Thousands of men and women are bidding farewell to the Notre-Dame construction site. To go into the cathedral without scaffolding and really enjoy the whole thing as spectators is something we're really looking forward to. An impatience shared by millions of tourists and worshippers deprived of Notre-Dame for five years, the world's most famous cathedral is finally ready to let everyone back in.