A railway tunnel at the new Saint-Denis Pleyel Grand Paris Express railway station in Saint-Denis. GETTY IMAGES

The Parisian subsoil, from the famous catacombs to the sewers and metro tunnels, is coming out of the shadows as the Olympic Games (26 July - 11 August) approach, along with the safety requirements that go with them. 

At the beginning of April 2024, French Interior Minister Gérald Darmanin warned that in order to secure the opening ceremony on the Seine, the authorities would have to deal with "extremely complex issues such as catacombs and tunnel networks" or "electrical and telephone networks".

"The subsoil is an opportunity for those who want to commit mischief," the Paris police prefecture (PP) told AFP. "The people of Paris are no more at risk than those of other major cities that have hosted the Olympic Games," the PP adds, "they will be subject to a security plan." 

Due to the discretionary nature of the access to these underground areas, which is theoretically forbidden, neither the Intervention and Protection Group of the police prefecture nor the Inspection Générale des Carrières (IGC), the city administration in charge of these underground areas, responded to the AFP's requests.

The 2022 IGC report mentions around thirty visible surface incidents (cracks, subsidence, collapses) in Paris and the same in the inner suburbs. The Paris City Council carries out "four to eight consolidation operations" a year, according to which "the general state of the quarry network in the City of Paris is relatively satisfactory". 

Should the quarries be closed to ensure the safety of the Olympic Games? According to Gilles Thomas, author of "The Underground Atlas of Paris" (published by Parigramme), of the almost 300 original entrances, the authorities have only left about a dozen accessible. And the fifty or so agents "have to move around all the galleries to monitor the stability of the network", according to the quarry expert. 

However, the catacombs and the Olympics "have nothing to do with each other", says Gilles Thomas. In fact, "if you superimpose the two maps" of the old underground quarries and the sports venues, "you will see that there is no Olympic site immediately above or close to these galleries of the capital's quarries". Moreover, they are too deep (an average of 20 metres) for a terrorist project, he points out. 

More than the 285 kilometres of quarries, known as catacombs and frequented by hundreds of cataphiles, according to Mr. Thomas, it is the almost 2,600 kilometres of sewers, just three metres below the pavement, that raise questions. Its tunnels, "entirely accessible on foot", follow "each of the 6,500 streets" of the capital, and this network "is accessible through more than 35,000" manhole covers, Gilles Thomas points out. "There is an entrance or exit" less than 50 metres from each Olympic site, he insists. 

When contacted by AFP, Antoine Guillou, the deputy mayor of Paris in charge of the sanitation network, remained tight-lipped."We have to close a certain number of entrances in order to comply with the security instructions" issued by the police prefecture, he said, assuring that these temporary closures "do not prevent the network from functioning".