The steeple of the landmark Notre-Dame Cathedral collapses as the cathedral is engulfed in flames in central Paris on April 15, 2019. - A huge fire swept through the roof of the famed Notre-Dame Cathedral in central Paris on April 15, 2019, sending flames and huge clouds of grey smoke billowing into the sky. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year. A spokesman for the cathedral told AFP that the wooden structure supporting the roof was being gutted by the blaze. (Photo by Geoffroy VAN DER HASSELT / AFP)        (Photo credit should read GEOFFROY VAN DER HASSELT/AFP/Getty Images)
GEOFFROY VAN DER HASSELT/AFP/AFP/Getty Images
The steeple of the landmark Notre-Dame Cathedral collapses as the cathedral is engulfed in flames in central Paris on April 15, 2019. - A huge fire swept through the roof of the famed Notre-Dame Cathedral in central Paris on April 15, 2019, sending flames and huge clouds of grey smoke billowing into the sky. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year. A spokesman for the cathedral told AFP that the wooden structure supporting the roof was being gutted by the blaze. (Photo by Geoffroy VAN DER HASSELT / AFP) (Photo credit should read GEOFFROY VAN DER HASSELT/AFP/Getty Images)
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Smoke rises in front of the altar cross at Notre-Dame Cathedral in Paris on April 15, 2019, after a fire engulfed the building. - A huge fire swept through the roof of the famed Notre-Dame Cathedral in central Paris on April 15, 2019, sending flames and huge clouds of grey smoke billowing into the sky. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year. A spokesman for the cathedral told AFP that the wooden structure supporting the roof was being gutted by the blaze. (Photo by PHILIPPE WOJAZER / POOL / AFP)        (Photo credit should read PHILIPPE WOJAZER/AFP/Getty Images)
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Smoke rises in front of the altar cross at Notre-Dame Cathedral in Paris on April 15, 2019, after a fire engulfed the building. - A huge fire swept through the roof of the famed Notre-Dame Cathedral in central Paris on April 15, 2019, sending flames and huge clouds of grey smoke billowing into the sky. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year. A spokesman for the cathedral told AFP that the wooden structure supporting the roof was being gutted by the blaze. (Photo by PHILIPPE WOJAZER / POOL / AFP) (Photo credit should read PHILIPPE WOJAZER/AFP/Getty Images)
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A woman reacts as she watches the flames engulf the roof of the  Notre-Dame Cathedral in Paris on April 15, 2019. - A huge fire swept through the roof of the famed Notre-Dame Cathedral in central Paris on April 15, 2019, sending flames and huge clouds of grey smoke billowing into the sky. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year. A spokesman for the cathedral told AFP that the wooden structure supporting the roof was being gutted by the blaze. (Photo by Geoffroy VAN DER HASSELT / AFP)        (Photo credit should read GEOFFROY VAN DER HASSELT/AFP/Getty Images)
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A woman reacts as she watches the flames engulf the roof of the Notre-Dame Cathedral in Paris on April 15, 2019. - A huge fire swept through the roof of the famed Notre-Dame Cathedral in central Paris on April 15, 2019, sending flames and huge clouds of grey smoke billowing into the sky. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year. A spokesman for the cathedral told AFP that the wooden structure supporting the roof was being gutted by the blaze. (Photo by Geoffroy VAN DER HASSELT / AFP) (Photo credit should read GEOFFROY VAN DER HASSELT/AFP/Getty Images)
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French Prime Minister Edouard Philippe (L), and French President Emmanuel Macron (3rd L) gather in near the entrance of the Notre-Dame de Paris Cathedral in Paris, as flames engulf its roof on April 15, 2019. - A huge fire swept through the roof of the famed Notre-Dame Cathedral in central Paris on April 15, 2019, sending flames and huge clouds of grey smoke billowing into the sky. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year. A spokesman for the cathedral told AFP that the wooden structure supporting the roof was being gutted by the blaze. (Photo by PHILIPPE WOJAZER / POOL / AFP)        (Photo credit should read PHILIPPE WOJAZER/AFP/Getty Images)
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French Prime Minister Edouard Philippe (L), and French President Emmanuel Macron (3rd L) gather in near the entrance of the Notre-Dame de Paris Cathedral in Paris, as flames engulf its roof on April 15, 2019. - A huge fire swept through the roof of the famed Notre-Dame Cathedral in central Paris on April 15, 2019, sending flames and huge clouds of grey smoke billowing into the sky. The flames and smoke plumed from the spire and roof of the gothic cathedral, visited by millions of people a year. A spokesman for the cathedral told AFP that the wooden structure supporting the roof was being gutted by the blaze. (Photo by PHILIPPE WOJAZER / POOL / AFP) (Photo credit should read PHILIPPE WOJAZER/AFP/Getty Images)
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TOPSHOT - Flames and smoke are seen billowing from the roof at Notre-Dame Cathedral in Paris on April 15, 2019. - A fire broke out at the landmark Notre-Dame Cathedral in central Paris, potentially involving renovation works being carried out at the site, the fire service said.Images posted on social media showed flames and huge clouds of smoke billowing above the roof of the gothic cathedral, the most visited historic monument in Europe. (Photo by Patrick ANIDJAR / AFP)        (Photo credit should read PATRICK ANIDJAR/AFP/Getty Images)
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(CNN) —  

Notre Dame’s centuries-old wooden roof beams, stone exterior and soaring Gothic architecture made Monday’s blaze especially difficult to tackle and Paris firefighters deserve praise for their efforts, experts say.

The spire and most of the roof of the centuries old cathedral have been destroyed, but the two bell towers and the main edifice were saved.

Video released by the French Interior Ministry showed the scale of the response. Authorities deployed some 400 firefighters, pumped water from the Seine and flew drones to survey the damage.

The biggest problem, experts say, was accessing the wooden ceiling beams which formed the frame for the soaring roof.

“It was pretty evident in the first 20 minutes that it was going to be a bad fire,” said Gregg Favre, a former firefighter with the St. Louis Fire Department in the United States.

The fire fighters would have been at a disadvantage “before they ever even pulled out of the firehouse,” added Favre.

The cathedral's ceiling contains thousands of oak beams, some of which date as far back as the 12th century.
Photographer:P. Lemaitre
The cathedral's ceiling contains thousands of oak beams, some of which date as far back as the 12th century.

Once the beams start burning, the stone exterior makes it harder for firefighters outside the building to get to the source of the flames. The stone traps heat and smoke, preventing them from working inside.

The Notre Dame’s height also posed a challenge, providing extra oxygen for the fire to breathe and complicating efforts to reach the flames.

“The fuel load is way up in the air, and the firefighters can’t get to it quickly,” said Glenn Corbett, associate professor of fire science at New York’s John Jay College of Criminal Justice.

Flames and smoke are seen billowing from the roof of the Notre Dame.
THOMAS SAMSON/AFP/Getty Images
Flames and smoke are seen billowing from the roof of the Notre Dame.

Video from the scene also shows firefighters using a robot named Colossus, built by Shark Robotics. The motorized robot, which can withstand extreme heat and connects to a fire hose, was maneuvered into the cathedral to spray the area with water.

Aerial options like the one suggested by US President Donald Trump were also considered unrealistic.

“Perhaps flying water tankers could be used to put it out. Must act quickly!” Trump said in a tweet.

But according to Corbett, no plane pilot could drop water “exactly in that one spot moving several hundred miles an hour over it.”

Corbett also ruled out the use of helicopters: “One of the issues you’ve got here, is that thermal updraft, that’s a chimney effectively, you can’t fly a helicopter in hot air. The air is so thin.”

Firefighters stand near Notre Dame.
JB Autissier/Panoramic/Reuters
Firefighters stand near Notre Dame.

The French civil security agency, Securite Civile, said in an apparent reference to Trump’s suggestion that any aerial water dumping could “weaken the structure of Notre-Dame and result in collateral damage to the buildings in the vicinity.”

Despite the huge challenges, the 400 firefighters were able to save a significant proportion of the cathedral.

Thomas Von Essen, a former commissioner of the New York City Fire Department who served during the September 11 attacks, said a photograph of the interior was encouraging.

“It’s not, you know, 30 feet of debris … stuff that’s going to be smoldering for days. It looks like they got this fire out,” said Von Essen.

Smoke rises in front of the altar cross the cathedral.
Philippe Wojazer/AFP/Getty Images
Smoke rises in front of the altar cross the cathedral.

“The fact that they were able to control the fire spread as much as they did and save a large portion of the building, including the two bell towers, it’s a tremendous effort,” said Favre.

“I think any firefighter that you ask that does this for a living would tell you that this is a significant firefighting event and those firefighters should be praised significantly.”