The fire was still raging at the Notre Dame Cathedral on April 15, 2019, when French President Emmanuel Macron vowed to renovate and reconstruct the medieval monument within five years.

Since then, work on the Gothic Episcopal church has been in full swing and is apparently on schedule.

The head of the construction site appointed by Macron, ex-general Jean-Louis Georgelin, sees great progress in construction.

"Thanks to strict planning, we are confident and determined to make the Paris cathedral open to worship and the public again in December 2024," Georgelin said in an interview with the newspaper Ouest-France.

He said that examinations of the building's fabric have shown that the cathedral's walls have remained stable despite the major fire, as have most of the vaults. Scaffolding is being removed from the northern and southern transepts and the first bays of the nave, he said. The stained glass windows and the large organ, which were spared by the fire, have been thoroughly cleaned, according to Georgelin, who added now that this phase has been concluded, the restoration of the interior willis set to begin. However, it is necessary to remain "vigilant and focused," the ex-general said.

Short circuit or cigarette caused the fire?

Exactly four years have passed since the fire. The historic building was partially destroyed in the process. The Paris fire department fought for four hours before it was able to confine the fire to the wooden roof truss. The west facade with the main towers, the walls of the nave, the buttresses and large parts of the ceiling vault, also the side aisles and choir ambulatories remained stable. Heat, smoke, soot and extinguishing water affected the church furnishings, but here, too, there was no major damage.

Whether the fire was caused by a short circuit or a construction worker's cigarette is still unclear.

The extent of the destruction was not as great as initially feared. "Thank God not all the vaults collapsed," German cathedral expert Barbara Schock-Werner said in a DW interview at the time. Only three vaults fell in the end.

There was a hole in the choir. The Gothic Madonna, meanwhile, remained intact, although the crossing tower came crashing down right beside her. "That is the miracle of Notre Dame," Schock-Werner said.

Window restoration in Cologne

Images of the burning cathedral went around the world. They triggered worldwide consternation and a wave of willingness to help.

French donors alone pledged €850 million ($940 million). But money and expertise also came from Germany. Schock-Werner took over the coordination of German aid.

Until a few days ago, Cologne Cathedral's construction lodge was restoring four stained glass windows that had been severely damaged by flames and heat. The four clerestory windows with abstract forms are the work of the French glass painter Jacques Le Chevallier (1896-1987), produced in the 1960s. In the glass workshop of the Kölner Dombauhütte, they were first freed from toxic lead dust in a decontamination chamber. The restorers then cleaned the window panes, glued cracks in the glass, soldered fractures in the lead mesh, renewed the edge lead and recemented the outer sides of the window panels. The restored "Cologne" windows have already begun their return journey to Paris, where they are being reinstalled and will be officially handed over at the end of July.

Sensational find after the fire

As dramatic as the fire was, a discovery by French researchers at the fire site was as sensational: iron clamps hold the stones of the structure together. Dating and metallurgical analyses revealed that these iron reinforcements date back to the first construction phase of the church in the 12th century. This may make Notre-Dame the world's oldest church building with such iron reinforcement. But more importantly, the mystery of why the nave was able to reach this height in the first place has also been solved.

When construction began in 1163, Notre-Dame with a nave more than 32 meters high was soon the tallest building of the time — thanks to a combination of architectural refinements: The five-nave floor plan, the cross-ribbed vaulting with thin struts, and the open buttress arches, also relatively thin, on the outside of the nave, which transferred the load of the structure from the walls, made the enormous height possible. Later cathedrals received iron reinforcements in addition to stone and wooden structures. It gave them stability.

People who visited Notre-Dame before the 2019 fire may hardly recognize it after the restoration. "Much more light will come in through the cleaned windows," said Lisa Bergugnat, curator of an exhibition on the cathedral at the Paris Architecture Museum. The walls, meanwhile, have also been cleared of soot and the grime of centuries. "The fire was ultimately also an opportunity to completely restore the cathedral," Bergugnat told the afp news agency.

That was impossible before, she said, because the church, with some 12 million visitors a year, could never be closed long enough. Also, the French state, which owns all church buildings built before 1905, would never have been able to finance such a costly restoration on its own, she argued.

The show at the Paris Museum of Architecture features charred pieces of wood, stone and metal objects from the cathedral, along with several works of art. Figuring out where the surviving pieces were installed was an "endless puzzle," the curator said. Much of the fallen stone had to be replaced. The same type of sandstone was found in quarries around Paris.

Reconstruction in the old style

For the reconstruction of the medieval roof truss, 2,000 oak trees were cut down. To work the trunks into beams, the craftsmen used special axes with the cathedral's facade engraved on the blade. They, too, are showcased in the Paris Museum of Architecture.

The showstoppers, however, are the statues of the twelve apostles and four evangelists that architect Eugene Viollet-le-Duc grouped around the ridge turret he designed in the 19th century. They survived the fire unscathed because they had been removed from the roof shortly beforehand for restoration.

The reconstruction of Notre Dame even sparked an architectural debate, mainly concerning the burned spire that marks the intersection of the transept and nave. The advocates of a modern version lost out, their argument that the defining tower was after all not designed until the 19th century went unheard.

The Institut Francais in Berlin currently offers an interactive journey through the 850-year history of "Our Lady of Paris," from the construction in the 12th century to its restoration after the devastating 2019 fire.