Indeed, Notre Dame was intentionally designed this way. The roof was built of wood so that if it caught fire, it could burn away, but the walls and other structures made of stone wouldn’t burn down. One big advantage of this architectural feature: The fire would be contained by the stone exterior and not put the rest of the city at risk.

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That appears to be what happened Monday, as the world watched in horror as flames shot through the 800-year-old structure. While the church was seriously damaged — the roof collapsed, the 300-foot spire crumbled, and parts of the wooden interior were charred — the fire appears to have done no harm to other buildings in the tightly packed Paris neighborhood where Notre Dame is located.

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“I think what people should understand is the ingenious approach by medieval builders,” said Kevin D. Murphy, a professor of art history at Vanderbilt University.

But some experts say that cathedrals and other places of worship built centuries ago are — at the least — hazardous to themselves, even if they were built with what passed in medieval times as cutting-edge, fire-containing safety measures.

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“Obviously, modern code was not written with cathedrals in mind,” said James W. Shepherd, director of preservation and facilities at Washington National Cathedral.

A big question will now linger over any plans to rebuild Notre Dame: Should it be rebuilt exactly as before, even if that includes replicating the flammable oak roof? Or will government officials force modern fire regulations onto an iconic building?

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“The technology of the building is not, of course, technology that we use anymore,” Murphy said. “In some cases, the actual technology has been under debate for centuries. Trying to understand how it was built is not straightforward.”

It will be a process watched closely around the world. Throughout history, there have been fires at cathedrals and similar buildings, including Old St. Paul’s in London, which burned during the Great Fire of 1666, and St. Mel’s Cathedral in Longford, Ireland, which was destroyed in a fire on Christmas Day 2009.

Kevin Fay, construction director at Gem Construction, which helped rebuild St. Mel’s, said some aspects of that blaze were similar to the Notre Dame fire on Monday.

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“The fire got onto the roof space, which was all timber” in St. Mel’s, Fay said. The roof subsequently collapsed: “You ended up with a huge inferno inside the cathedral. The fire got to such high temperatures that the actual marble and stone crystallized."

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Some of the damage at St. Mel’s came from the cold water sprayed over the site by fire services to put out the blaze, causing the masonry to rapidly contract. “You could hear the stonework cracking for days afterward,” Fay said.

Shepherd, of Washington National Cathedral, said that, historically, smaller churches were most prone to fire, as they were made entirely of wood. But the case of Notre Dame shows that the heavy wooden roof structures of some larger cathedrals also were a risk.

“The attic is out of sight, out of mind,” Shepherd said. “If something starts there, it’s harder to detect.”

Modern tactics for containing a fire — by compartmentalizing it in a small space — are hard to implement in a cathedral, which is by design an enormous open space.

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The vastness of Notre Dame, as well as its symbolic value, will put pressure on those seeking to renovate it. The task of restoration is “hugely daunting because it’s such a huge building. It can only be daunting,” Murphy said.

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Before restoration begins, there will need to be a survey of the damage. In the case of St. Mel’s, the damage was so extreme that experts weren’t allowed to walk into the building out of fear over its structural integrity.

Instead, they entered the building through the now-removed roof, using mobile platforms and cranes.

Speaking Tuesday after the blaze was put out, French Junior Interior Minister Laurent Nunez told reporters that the overall structure of Notre Dame appeared to be intact but that there were “some points of vulnerability,” including in the vault.

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Gregory Bryda, a specialist in the architecture of medieval Europe at Barnard College, wrote in an email that the process of restoration probably will take years.

“The most significant hurdle going forward will be to shield not only the gaping holes in the cathedral’s ceiling but also, frankly, the entire building from the elements, since the roof functioned to siphon off the rain,” Bryda wrote.

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Rebuilders will face major decisions about whether to remake the structure using traditional techniques or their more modern counterparts. Many of the older techniques are difficult to reproduce in the 21st century.

The roof of St. Mel’s, for example, may look very similar to its original, but hidden within the timber structure are modern steel connective joints, according to Fay. Modern timber simply isn’t as strong as the slow-grown timber that was used in construction years ago.

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There will also have to be major decisions about what sort of modern fire systems to install, such as sprinklers that could put out a fire but potentially damage artwork and other valuable objects.

The challenge of rebuilding will be “immense,” according to Jean-François Bédard, an associate professor specializing in French architecture at Syracuse University. But in a certain sense, using exactly the same materials and restoring the building to what it was would be less in keeping with the history of the cathedral than innovating.

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“It’s not the first time” Notre Dame has been rebuilt, Bédard said. “Not to say that this is not catastrophic. But it’s not the first time these buildings are being rebuilt.”

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The cathedral was restored in the 19th century by two architects, Jean-Baptiste Lassus and Eugène-Emmanuel Viollet-le-Duc. The spire that collapsed Monday was designed then. Much of what is known today as Notre Dame was based on “medieval visions of 19th-century architects,” Bédard said.

One thing isn’t up for debate: Any restoration or repair will take plenty of money and a lot of time. The restoration of St. Mel’s took $33 million and five years. Even with the vast sums of money already pledged for Notre Dame, it’s a far larger building at the heart of one of Europe’s largest and most expensive cities.