French Politics

But for Notre Dame, Hugo’s book sparked fresh problems. The best seller inspired a restoration in 1844, which used low-quality stone and even cement, since France at the time could not produce the quantities of high-grade material that the job required.

Nearly 200 years on, that 19th century work is crumbling (though the medieval construction is mostly in better shape). One blazing hot day in early July, a staff member unlocked an old door off the choir and led TIME up a stone spiral staircase and out onto the roof, high above the crowds. Here, the site seemed not spiritually uplifting but distressing. Chunks of limestone lay on the ground, having fallen from the upper part of the chevet, or the eastern end of the Gothic church. One small piece had a clean slice down one side, showing how recently it had fallen. Two sections of a wall were missing, propped up with wood. And the features of Notre Dame’s famous gargoyles looked as worn away as the face of Voldemort. “They are like ice cream in the sun, melting,” says Michel Picaud, head of the nonprofit Friends of Notre Dame de Paris, looking up at them.

What is more, some fear the problem is getting worse. “The damage can only accelerate,” says Andrew Tallon, an associate professor of art at Vassar College in Poughkeepsie, N.Y., and an expert on Gothic architecture. Having carefully studied the damage, he says the restoration work is urgent. If the cathedral is left alone, its structural integrity could be at risk. “The flying buttresses, if they are not in place, the choir could come down,” he says. “The more you wait, the more you need to take down and replace.”

The church was not fully aware of the extent of the problem, say those at Notre Dame. Until a few years ago, the government effectively made the private areas off-limits. “There used to be about 200 old keys, so it was very, very difficult,” says André Finot, a spokesman for Notre Dame. Eventually, the government standardized the keys and allowed its tenants to climb the hidden stone staircases and access the upper levels. “We were shocked when we got up there,” Finot says.

Much remains to be learned. But already it is emerging that Notre-Dame, irreplaceable as it is to France’s heritage, lacked the fundamental fire-prevention safeguards that are required in more modern structures and have been grafted onto other ancient cathedrals elsewhere in Europe.

Some of those elements, like firewalls or a sprinkler system, were absent by choice — so as not to alter the landmark’s design or to introduce electrical wiring deemed a greater risk amid the timbers that supported Notre-Dame’s ornate lead roof.

“There had been a systematic refusal to install anything electrical” within “the forest” because of the risk, said Pierre Housieaux, president of the Paris Historical Association. “Everyone knew that the attic was the most fragile part.”

Inevitably, some of those decisions are being called into question in the aftermath of a calamity that scarred a jewel of Gothic architecture precious to all the world, and left a gaping wound in the heart of Paris.

“The fire-detection system existed, not the fire compartments,” said Jacques Chanut, president of the French Building Federation, referring to the structures commonly used elsewhere to contain blazes. “That’s the typical example of something we are going to have to think about tomorrow.”

However it began, the fire galloped unimpeded across the attic and roof, and up the wood structure inside the spire. The flaming spire stood out over the city like a Roman candle until it toppled over, crashing through the ceiling and into the cathedral.

As flaming pieces of the upper structure fell to the cathedral floor, some of the interior furnishings also caught fire.

Firefighters deployed a robot equipped with tank-type treads and a camera to pull hoses into the cathedral and aim water at the flames. Firefighters also used aerial drones to get a view, including thermal imaging, into the inferno.

But in the absence of fire-prevention measures at the cathedral, there was only so much the firefighters could do.

“The lack of fire security allowed the fire to spread quickly,” said Jean-Michel Leniaud, the former director of the École Nationale des Chartes, a French university institute that specializes in the sciences supporting historical work. “If there were sprinklers everywhere it might have been different, but there weren’t.”

Mr. Leniaud, who visited the interior of Notre-Dame on Tuesday, said the state, which owns and maintains the cathedral, had fire safety regulations for all buildings, but that “sometimes they can be hard to apply.”

Paradoxically, that can be especially so for some of its most cherished structures. “There’s always been a hesitation to disfigure the monument in question,” Mr. Leniaud said.

One reason the fire swept through the open space beneath the roof is that there were no barriers — sometimes called firewalls — to compartmentalize the blaze until firefighters could arrive, said Jim Lygate, a visiting professor of fire investigation at University of Edinburgh. For that reason, he said, such barriers are legally required in similar structures in Britain.

Before the blaze, restoration work had begun and much of the building was sheathed in scaffolding, which was still being erected. Julien Le Bras, the chief executive of Le Bras Frères, the company that handles the cathedral’s scaffolding, told reporters that 12 employees worked on the site, but that none were there when the fire started.

Experts say that restoration, which often involves combustible chemicals and electrical tools, always presents a fire danger, as does electrical wiring

The Notre-Dame restoration project was to focus on reinforcing the spire and repairing some of the attic beams, said Olivier de Chalus, a construction engineer and volunteer guide at the cathedral. He described the structure under the roof as “the cathedral’s jewel, the true piece of art that wasn’t accessible to many.”

But experts say the beams, many of them dating to the cathedral’s construction in the 12th and 13th centuries, became tinder-dry as they aged.