As Notre-Dame in Paris burned, US President Donald Trump tweeted some advice to French firefighters.
"Perhaps flying water tankers could be used to put it out. Must act quickly!"
But doing that would have brought the ancient cathedral crashing down, French fire chiefs told AFP Tuesday.
"Everything would have collapsed," said Lieutenant-Colonel Michael Bernier, a fire chief who speaks for the national civil defence organisation and who described the suggestion as "risible".
Releasing even one load from a Canadair water bomber used to fight forest fires on Notre-Dame would be "the equivalent of dropping three tonnes of concrete at 250 kilometres per hour (155mph)" on the ancient monument.
"It would have been like bowling with the cathedral... the two towers might have fallen.
"It was technically impossible, undoable and most of all would have been utterly useless" to douse the flames from the air, Bernier added.
In fact, dropping a 6,300-litre (1,664-gallon) load from a Canadair water bomber would have put the lives of firefighters and anyone in the area at risk, he added.
"Neighbouring buildings would have been hit by flying blocks of hot stone, and the whole area would have had to be evacuated."
- 'Might have tumbled' -
With more than 500 firefighters already at the scene -- many within the building -- that would have been impossible.
Even using a helicopter to drop 1,500 litres of water would have left only the towers standing, Bernier insisted.
"The nave would have collapsed, the flying buttresses would have gone," he said.
"If a plane had been used the whole of the structure might have tumbled."
Lieutenant-Colonel Gabriel Plus of the Paris fire brigade said that "everything was against" the first firefighters who had to battle the French capital's evening rush-hour to get to the scene on Monday.
"Time and the wind was against us and we had to get on top of it fast. We had to make a rapid choice... and the priority we gave ourselves was to save the two bell towers, and both were saved," he added.
"Imagine if the woodwork in the belfries had been weakened, the huge bells would have collapsed" and that might have brought the towers down.
"That was really our fear," said the senior officer, who acts as the fire brigade spokesman.
"From the beginning, there was always the possibility that the whole structure might collapse."
While armchair critics have suggested more could have been done to slow the fire, tough choices had to be made, said Plus.
"With a part of the roof already in flames it was no longer saveable," he said.
- Robot helps save nave -
"So we put our efforts into protecting the two belfries and getting our people into the interior to save the works of art inside.
"Once we saw that the spire would fall we got our people out and concentrated our efforts on the exterior," he added.
Plus said a robot was sent into the building after the firefighters were evacuated to hose the interior of the building to "lower the temperature of the nave".
Experts credited this with helping save the cathedral's organ and its spectacular rose windows from the worst of the flames.
The fire chief said the next few days will be spent making sure the fire has been well and truly extinguished and that "the structure is stabilised".
"We have teams with laser equipment who are checking the structure for movement. They will be checking the whole of Notre-Dame -- from the towers and the vaulted ceiling to the walls to assess their fragility."
As Notre-Dame Cathedral went up in flames, French fire officials said flying water tankers -- as suggested by Donald Trump -- would have brought the building crashing down