Our TGV heading east from Paris to Metz in Meurthe-et-Moselle was one of the very few not cancelled on March 16. Did the striking rail workers know the whole world was going to be on that train heading to Lorraine? I liked the thought that the angry trade unionists spared us, just this once, for a greater cause: Notre Dame.

I left home before dawn weirdly excited by this invitation to a most peculiar dress rehearsal. I was to witness the assemblage of the base of Notre Dame’s spire, the first stage of the reconstruction. Made of the largest oaks to be found in France, namely the former royal forest of Bercé in Sarthe, the base of the spire is called tabouret in French, or stool, and on it sits the 66-metre-high spire, rising in the Paris sky to 96 metres.

After an hour’s drive from Metz, our bus filled with foreign languages like a tower of Babel on wheels, we arrived in Val de Briey, a small town near the border with Luxembourg. Another coach carrying the architect-in-chief Phillipe Villeneuve and the five-star general overseeing the operations, Jean-Louis Georgelin, was already there. This green valley is where four family-owned artisan companies have set up their joint ‘atelier,’ a hangar big enough to saw, cross-cut, rip-cut, carve, and bisect massive oaks that will make the future flèche of the Paris cathedral that burnt down almost four years ago. Together, Le Bras Frères, Asselin, Cruard Charpente and MdB Métiers du Bois have joined forces to rebuild the roof and spire of Notre Dame de Paris.

The ‘companions of duty,’ as those artisans are called, are the crème de la crème of their trade and all specialised from an early age in the repair and restoration of historical monuments. They have learnt centuries-old methods, and use the same tools as Medieval and Renaissance craftsmen. For them, to be part of this adventure is the opportunity of a lifetime. ‘There will never be anything like this for us all,’ the 27-year-old carpenter Paul Poulet told me that afternoon.

What this assemblage rehearsal allowed them to do was to check that every piece of this giant wood jigsaw perfectly fitted together before they transport the ensemble to Paris’s Île de la Cité and start erecting it to stand for all eternity. For them, perfection is not a luxury: the base of the spire will be resting on the four pillars at the crossing of the transept, and will carry the entire weight of the whole spire (including 450 tons of wood). It needs to be flawlessly assembled to fully play its supporting role.

Fifteen metres long, 13 metres wide, and six metres high, the spire’s base is made of 110 different pieces. Among the most impressive are the two 20-metre-long diagonal beams made from eight exceptionally large oaks. Transported to Paris before the end of the month, the base will be placed above the vaults at a height of 30 metres. The scaffolding will then start rising in sync with the spire and eventually reach 100 metres. ‘Are you afraid of heights?’ I asked Poulet. He smiled. Of course, he is not. ‘But it will be windy out there,’ he added. The higher they go, the narrower, the windier, and the more dangerous.

There will be five stages in the spire’s reconstruction. As designed by Viollet-le-Duc, its 1840s architect, the spire is made of five pieces. They have poetic names: tabouret (stool), souche (stump), fût (cask), étage ajouré (hemstitched floor) and aiguille (needle). While a team of carpenters adjusts one piece above the transept, another prepares the next one in their Lorraine hangar, so that no time is wasted. After all, both the architect-in-chief and the general have pledged to deliver President Macron’s promise and reopen the cathedral to the public and to worship in 2024. At Val de Briey, Villeneuve declared: ‘Notre Dame will reopen on December 8 at 11.15 am.’ The general joked: ‘We may be fifteen minutes late.’