When President Macron said they would get Notre-Dame de Paris up and running inside just five years, everyone laughed.
They're not laughing now.
The promise to save the devastated cathedral in so short a space of time seemed back then like a typical bit of Macronian bombast.
But on the fourth anniversary of the conflagration, the prospect of a Notre-Dame refitted by the end of next year no longer seems so absurd.
"We made an undertaking in front of the whole world that we would have our cathedral finished inside five years," says Jean-Louis Georgelin, the retired army general in charge of reconstruction.
"Our reputation is at stake. That is why we must unite all our knowledge, our efforts, our savoir-faire to achieve this goal."
If the rebuilding project has a symbol then it is the cathedral's 66 metre (217ft) spire, whose dramatic collapse into the flames was the appalling climax of the April 2019 disaster.
Today, in a sign of the burgeoning optimism, a replacement spire is being completed at an industrial site in eastern France.
Built from hundreds of oak trees raised and felled in ancient French forests, the base of the spire - it alone weighing more than 80 tonnes - was transported in the last few days to Paris and hoisted to the roof of the cathedral.
It had to be measured with utter precision in order to slot into the corners of the mediaeval masonry where the original architects had put their first roof frame 900 years ago.
"In the coming months Parisians will see the spire beginning to rise. First it will be surrounded by scaffolding, but at the end of the year they will see it unveiled," says Gen Georgelin.
"That is when they will know for real that the cathedral is being returned to them."
The spire may have been a much-loved part of the Paris skyline, but - as Parisians have been reminded over and again - it was not actually part of the medieval building.
In fact it was only put in place in the mid-19th Century, to replace the original spire that had been dismantled around the time of the French Revolution because it was unstable (or maybe so the government could get its lead!).
It was in the same period that many of the cathedral's stained glass windows were also replaced - the originals having become too fragile.
Fortunately none of the stained glass was seriously damaged in the conflagration. The firefighters knew their business and refrained from spraying water on the glass. Otherwise in the heat it would have shattered.
The medieval rose windows have been left in place, but much of the rest of the stained glass was removed and is now being cleaned by specialists in workshops around the country.
"There are nearly 200 years of accretions," says Troyes-based glassmaker Flavie Vincent-Petit.
"There is the human grease from the breath of millions of worshippers; there is the soot of millions of candles; there are the stains of condensation. It all leaves a mark."
Inside Notre-Dame it is still a futuristic film décor - a towering mass of rectilinear metal scaffolding set against the curves and arches of the ancient Gothic stone.
In addition to the spire, work is proceeding on the sections of elevated masonry that fell in. The roof's entire wooden substructure is also being replaced - as far as possible in an exact replica of what was destroyed.
Philippe Villeneuve, the cathedral's chief architect, described himself four years ago - after witnessing the fire - as "the unhappiest architect in the world".
"But today I am the happiest," he says. "I am watching it being reborn like a phoenix from the ashes."
The target is to celebrate a first mass in the newly-reopened Notre-Dame in December 2024.