As the Notre Dame Cathedral went up in flames early on Monday evening, devastated Parisians gathered on the banks of the Seine and wept, while dazed tourists looked on aghast.
With the world reeling at the devastation of a landmark beloved across the globe, politicians and luxury goods billionaires pledged to donate to a fund to rebuild the 12th-century cathedral.
But precious architectural features of the building were reportedly burned beyond recovery in the devastating blaze.
France's President Emmanuel Macron warned the fire could continue burning for days, saying "the battle is not yet totally won".
The 12th-century cathedral is home to incalculable works of art and is one of the world's most famous tourist attractions. Many of its religious artefacts — including a crown of thorns believed to have been worn by Jesus Christ — are said to have been preserved by brave firefighters who risked their lives to recover them.
The exact cause of the blaze was not known, but the Paris fire brigade said the fire is "potentially linked" to a six million euro ($9.48 million) renovation project on the church's spire, and its 250 tons of lead.
The Paris prosecutors' office earlier ruled out arson and possible terror-related motives, and said it was treating the fire as an accident.
Wooden latticework inside the 12th-century cathedral is said to have been fuel for the destructive fire. A spokesman for Notre Dame told reporters on the ground that the flames were consuming the historic woodwork, which dates back hundreds of years and has a rich history.
The wooden framework is primarily oak and dates back to the original framework first built for the cathedral. The trees used for Notre Dame's frame were cut between 1160 and 1170, and make up the oldest parts of the structure.
The beams used were old growth — about 300-400 years old — so they were tall enough for the buildings high, vaulted ceilings.
The framework in place at the time of the fire dated back to the year 1220, according to the Notre Dame website. The internal "forest" structure was so named "because of the large number of beams that had to be used to set it up, each beam coming from a different tree", which was harvested from a nearby wooded area.
It's estimated the workers felled 13,000 trees to make up the internal latticework, with the strong oak beams holding up a roof of heavy lead tiles. The site notes that the original internal forest of woodwork in the choir section has been replaced, suggesting it may have previously been destroyed by a fire.
The cathedral is home to countless other priceless artefacts of significance to Catholics, other Christians and lovers of art.
The Rose Windows are immense and elaborate stained glass, overlooking the three main wings of the cathedral. Dating back to the 13th century, the windows are reported to have survived the fire.
A series of 76 four-metre tall paintings depict the New Testament's Acts of the Apostles, including the crucifixion of St. Peter and the conversion of St Paul. These paintings date from 1630 to 1707 and were created by members of the Royal Academy of Painting and Sculpture.
Other treasured artefacts inside include what is believed to be the crown of thorns worn by Jesus Christ, a fragment of the True Cross and one of the Holy Nails.
Local firefighters formed a "human chain" to save these relics, entering the Gothic building to rescue treasures including the crown of thorns and the tunic of Saint Louis.
Catholics believe the sacred thorns were worn by Jesus while he was crucified.
Is there anything firefighters could have done to control the blaze that tore through Paris' historic cathedral sooner?
Experts say the combination of an 850-year-old structure, heavy timber, soaring open spaces and a lack of sophisticated fire-protection systems left firefighters with devastatingly few options once the flames got out of 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 — more like gardening equipment than firefighting apparatus — as flames raged across the cathedral's wooden roof and burned bright orange for hours. The fire toppled a 91-metre spire and launched baseball-sized embers into the air.
While the cause remains under investigation, authorities said the cathedral's structure — including its landmark rectangular towers — had been saved.
Some 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 US Fire Administrator 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 Mr Bryant, a former Oklahoma fire chief 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," Mr 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."
Paris's narrow streets make it difficult to manoeuvre large ladder fire trucks, so European fire departments don't tend to have ladders as big as those in the United States, he said.
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 has at least four fire inspections a year.
Washington National Cathedral — built in 1912 with steel, brick and limestone materials 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. It holds fire inspections every two years, but DC firefighters visit 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 Notre Dame 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," he said.