Experts say the combination of a structure that's more than 850 years old, built with heavy timber construction and soaring open spaces, and lacking sophisticated fire-protection systems led to the quick rise of flames Monday, which jeopardized the entire cathedral before firefighters brought the blaze under control.

"Very often when you're confronted with something like this, there's not much you can do," said Glenn Corbett, a professor of fire science at John Jay College.

Fire hoses looked overmatched as flames raged across the cathedral's wooden roof and burned bright orange for hours. The fire toppled a 300-foot (91-meter) spire and launched baseball-sized embers into the air.

While the cause remains under investigation, authorities said that the cathedral's structure - including its landmark rectangular towers - has been saved.

Some of the factors that made Notre Dame a must-see for visitors to Paris - its age, sweeping size and French Gothic design featuring masonry walls and tree trunk-sized wooden beams - also made it a tinderbox and a difficult place to fight a fire, said U.S. Fire Administrator G. Keith Bryant.

With a building like that, it's nearly impossible for firefighters to attack a fire from within. Instead, they have to be more defensive "and try to control the fire from the exterior," said Bryant, a former fire chief in Oklahoma and past president of the International Association of Fire Chiefs.

"When a fire gets that well-involved it's very difficult to put enough water on it to cool it to bring it under control," Bryant said.

And while there's a lot of water right next door at the Seine River, getting it to the right place is the problem, he said: "There are just not enough resources in terms of fire apparatus, hoses to get that much water on a fire that's that large."

Because of narrower streets, which make it difficult to maneuver large ladder fire trucks, European fire departments don't tend to have as large of ladders as they do in the United States, Bryant said.

And what about President Donald Trump's armchair-firefighter suggestion that tanker jets be used to dump water from above on Notre Dame?

French authorities tweeted that doing so would've done more harm than good. The crush of water on the fire-ravaged landmark could've caused the entire structure to collapse, according to the tweet.

Other landmark houses of worship have taken steps in recent years to reduce the risk of a fire.

St. Patrick's Cathedral in New York City, built in 1878, installed a sprinkler- like system during recent renovations and coated its wooden roof with fire retardant. The cathedral also goes through at least four fire inspections a year.

Washington National Cathedral, built in 1912 with steel, brick and limestone construction that put it at less risk of a fast-moving fire, is installing sprinklers as part of a renovation spurred by damage from a 2011 earthquake.

That cathedral faces fire inspections every two years, but D.C. firefighters stop by more often to learn about the church's unique architecture and lingo - so they'll know where to go if there's a fire in the nave, or main area of the church - for instance.

"It's really important for us to make sure that those local firefighters are aware of our building and our kooky medieval names that we use for all the different spaces and that they know where to go," said Jim Shepherd, the cathedral's director of preservation and facilities.

Cardinal Timothy Dolan, the New York Archbishop who often visited the Notre Dame Cathedral while studying in Europe, saw significance in the fact that the fire broke out at the beginning of Holy Week, when Christians there and around the world prepare to celebrate Easter and the resurrection of Jesus Christ.

"Just as the cross didn't have the last word, neither - for people of faith in France - will this fire have the last word," Dolan said.

AP