In the early evening of Monday, April 15 2019, as a Mass to celebrate Holy Week was being held at Notre-Dame in Paris, a fire alarm went off in the cathedral’s security control room. It was 6.17pm. The fire security officer, working a double shift on his first day on the job, read the panel and radioed to alert one of the guards. He went to investigate what he understood to be a fire in the attic of the sacristy, and found nothing. An evacuation announcement was brushed off as a false alarm, and worshippers were invited back into the building.

Yet fire had taken hold – not in the sacristy, but in the attic of the nave, an area known as the “forest”, where a lattice of 900-year-old oak beams held up the roof. After a crucial half-hour delay, by which time smoke was being photographed billowing above the cathedral by tourists outside, the seat of the fire was discovered. 

With no sprinkler system, nor fire walls to slow the spread, it was soon burning out of control. President Emmanuel Macron arrived in time to see the 19th-century spire collapse and crash through the vault of the nave. As the world watched on, the flames spread to the belfries, and the complete destruction of one of the most visited buildings in Europe seemed inevitable. 

Miraculously, thanks to a small group of firefighters who volunteered to go back towards the intense heat – temperatures peaked above 1,200C – Notre-Dame was saved, and no lives were lost.

Now, with his new film Notre-Dame on Fire, director Jean-Jacques Annaud (The Name of the Rose) has turned these real-life events into one of the most compelling dramas of the year. Approached with the idea of making a documentary, the 78-year-old Oscar winner, whose other films include Enemy at the Gates and Seven Years in Tibet, saw the dramatic potential of recreating the fire when he began researching precisely what had happened. 

Annaud set about contacting those who were involved on that fateful evening – conducting more than 150 interviews – “and what they revealed to me was far more bizarre, more incredible, or should I say, not credible – yet it was the truth.” 

In fact, so many new details came out, he says, that “I was asked to see the justice department, which I refused because I am a film-maker and I don’t belong to the police department. But I’ve learnt so many things, even after finishing the movie... people will tell a film-maker things that they wouldn’t trust to the justice department.”

These included documents from a French chemist at Shanghai University, which showed that the timbers had been sprayed a year earlier with an anti-fungal gel – Xilix Gel Fongi+ – that made them more flammable. “Neighbours from the very narrow streets close to the cathedral had remembered the smell of it being applied … it was on all of the carpentry. 

“I learnt from the factory that the spray comes with a warning: ‘In case of fire, never use water.’ Because water on that product will intensify the size of the flames. I said it to the firemen. I had the impression that they had no idea … that they were not informed.

“There were so many mistakes, so many malfunctioning elements. Everything that could go wrong, went wrong.”

Traffic in Paris came to a standstill as fire crews tried to get to the scene. Once on the Île de la Cité, in the middle of the Seine, where Notre-Dame stands, firefighters had to deal with inadequate water pressure, punctured hoses, and spiral staircases so tight that they had to climb over one another to pass. 

Meanwhile, the man with the key required to rescue one of the most sacred relics in all of Christendom, the Crown of Thorns, purchased by Louis IX in 1238 for 13,134 gold pieces, was at a soirée in Versailles, and had taken said key with him.

Louis had almost bankrupted France to secure the crown from Venetian merchants. “It put France in terrible debt for 35 years, because it cost the budget of the kingdom for one year,” says Annaud. “Today it would be like £2 trillion.” As for the crown’s authenticity, “I could not interview any witness of the Crucifixion,” he says, “but what I can tell you is there are mentions of this crown dating back to the second century, when we know that it was kept in Jerusalem.” 

Yet what shocked Annaud was that the relic initially rescued from its display case at Notre-Dame was merely a replica of the one that had been brought from Constantinople. “I couldn’t believe the fact that for 30 years, people came from the other end of the world to kneel and pray in front of that fake which, when we recreated it, cost us two euros to make, with some wire and one of those [gold] sprays that you buy for Christmas. It was mind-blowing.”

The real crown was in a safe, which needed general manager Laurent Prades, who was racing to get back from Versailles, to turn the key according to a code. That was if he could get through police lines (he was turned back) and remember the code (he couldn’t). He had to break through and run, then phone another code holder beside the safe itself, with what he described as “incandescent pieces of wood” falling around him – “the nave littered with burnt beams … the vaults pierced”. Annaud takes this ticking-clock disaster-movie material and cranks up the tension everywhere you look. He also deals head-on with one of the most controversial elements of the battle to save Notre-Dame.

It had become clear that only an effort to quell the fire in the belfries could save the cathedral, which dates from 1163 and had survived the French Revolution and the Nazis. Most were convinced it would collapse. Fire chiefs were unwilling to risk the lives of firemen and women in what seemed like a suicide mission, but when volunteers came forward, it appears that the officer in charge asked Macron to take responsibility for it to go ahead. 

“This is the way it has been told to me,” Annaud says. “I have the original footage, with the [fire brigade] generals and with Macron, with the prime minister, with the préfet of police.” He uses the real footage to restage the moment. “It ends the way I did it. It was not the same editing as on French television, where you had the impression that Macron said yes. He never did that.” 

He did, however, give a wink. “The image you see of Macron putting his hand on the shoulder of the general, blinking his [right] eye, is exactly what happened … And it was known among the firemen … But I must insist on one thing – a president of the republic is chief of the military, but is not the person that should make decisions on the battlefield. But basically, he didn’t say no, this is what we can say.” His silence was taken as consent. The volunteers put out the fire. 

Fire brigade adjutant Rémi Lemaire, whose plan it was, had been ordered to evacuate the south tower, but had been determined  to “get a visual” of the fire. He then suggested “getting the water up to the Chimera Gallery. We were some 20 men to embark on the operation and, indeed, I can say it was no small feat!” There was no escape route if it went wrong. 

Annaud was committed to sticking to the facts. The film begins with a dedication from 18th-century epigrammatist Antoine Rivaroli: “Everything is true, as implausible as it seems.” But the director did allow himself a depiction of the fire’s possible causes: a burning cigarette-butt dropped by one of the workers working on scaffolding on the cathedral, who would have clocked off at 6pm (“the police know exactly who smoked, because they retrieved the cigarettes and analysed the DNA of dozens of people … although it’s absolutely forbidden”); a pigeon pecking an electrical cable; reported threats against Notre-Dame made by jihadists. But he does not attempt to draw a definitive conclusion. Also, with limited opportunities to shoot on location, we see the cathedrals of Sens, Bourges and Amiens, as well as a huge studio-built set, standing in for Notre-Dame itself. 

For Annaud, who studied medieval art and history, making the film tapped into a lifelong passion. Though an atheist from a secular family, he tells me, “as an 11-year-old, I wanted to do a catalogue of the not-known cathedrals of France, and I started it, I have thousands of pictures that I took in that period”. Notre-Dame, he notes, “still has this perfume of the Middle Ages”. He lives nearby, at Pont Neuf. 

Yet he admits he was not an admirer of the 19th-century additions made by Eugène Viollet-le-Duc, in the neo-Gothic style. “What he did is a Romantic rebuild of the cathedral. It’s a distorted vision of early Gothic art, more of a Victorian look. But my belief is that the spire was way too heavy for the transept crossing, it was very dangerous.”

One of the unexpected results of the fire, he says, was that the cathedral, which was struggling to fund much-needed restoration at the time, has “enough money now to restore the cathedral and make it strong enough for the next 1,000 years”. (It received £865 million in donations.) Yet 100 cultural figures have spoken out against a proposed revamp of the interior involving mood lighting and modern art, which has been approved by French authorities. Macron’s plan for a contemporary design to replace the spire, meanwhile, has been abandoned after an outcry. Fortunately, Notre-Dame’s famous rose window made it through the blaze.   

What was the one thing Annaud was most glad to have seen survive the flames? “Hope,” he says. He compares the burning of Notre-Dame with the destruction of the Twin Towers. “It was far beyond a monument that was on fire,” he notes. “Here we have something sacred… It’s a symbol of not only faith, but of Western civilisation … It’s beyond Europe.”

Notre-Dame on Fire is in cinemas from today