Firefighters stood helpless to stem the blaze Monday at Notre Dame Cathedral, likely because of Gothic engineering techniques that waterproofed the roof, consigning it to destruction.

The roof and spire of Notre Dame were all but doomed to burn once flames began to spread, possibly begun by a renovation accident,
according to Ted Henderson, who studied archaeology at Dartmouth College. Henderson said a Gothic engineering technique used to waterproof the top of the cathedral involved placing a lead sheet roof over a wooden truss structure on top of the groin vault that served as the ceiling of the cathedral’s nave.


The wooden truss became highly flammable as it dried over hundreds of years, but was completely sealed from the outside by the lead sheets, and therefore impervious to firefighters’ efforts to douse the flames with water, Henderson said.

“So the wood catches on fire and it’s not actually exposed to the outside of the building anywhere,” Henderson told The Daily Caller News Foundation.

“In fact, the reason the roof is covered with lead is so water can’t get inside. It’s specifically fireproofed. So when the firemen, you know, arrive on the scene and they’re spraying [the] cathedral with water, it’s running off the sides of the lead roof and can’t access this void where the fire is actually spreading.”

As the fire grows hotter, the lead super-heats and melts, falling down onto the stone vault of the nave, which overloads the vault and causes it to collapse inward, creating an imbalance of weight throughout the entire structure and possibly leading to a total collapse, Henderson said.

A number of Gothic cathedrals have suffered near total collapses due to fire throughout history, including the Papal Basilica of St. Paul Outside the Walls, which burned in 1823 because a workman repairing the lead roof accidentally began a fire.

The walls of Notre Dame, however, do stand a chance of remaining upright.

“The best case scenario at this point is you’re going to get a shell, an exterior shell over the building. Maybe with the bell towers still standing,” Henderson said.

While the roof, spire, and all of the stained glass windows of Notre Dame are tragic losses, Henderson told The Daily Caller News Foundation, the fire also endangered one of the most sacred Christian relics in history, housed behind the cathedral’s altar—the crown of thorns worn by Christ.

“This is like one of the very, very few [relics] that might actually be legitimate and real in the cathedral and almost certainly destroyed,” Henderson said of the crown of thorns. “It sits right behind the altar at the rear of the cathedral. And if you look at the videos right now, the area immediately above it is completely engulfed in flames.”

One French journalist, however, reported that the crown of thorns, works of art, and the sacraments in Notre Dame were somehow saved from the fire. Further sources have yet to confirm that.

The crown of thorns was kept in Constantinople during the Byzantium empire until Emperor Baldwin II offered it to King Louis IX of France in exchange for hefty financial support of his nearly bankrupt empire. The crown of thorns was considered at the time to be “the most valuable single object in the face of the earth,” according to Henderson.

The crown of thorns has been in near continuous royal possession since Constantine the Great, with the exception of the time between when it was stolen during the French Revolution and when it was returned.

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