[Photo: Stephen Alvarez for National Geographic, February 2011]

Over 1900 acres of the city’s building fabric sits atop unstable ground. The harvesting of the Left Bank’s limestone and gypsum base has created a dense network of underground tunnels, canals, reservoirs and vaults – effectively resulting in a sponge-like foundation for the city.

The extraction began as early as 2000 years ago when Roman settlers began harvesting the stone.  During the latter parts of the Middle Ages the quarrying supplied material for Paris’ construction boom.  While these sites where originally located beyond the city’s edges, Paris continued to grow outward and the subterranean quarry sites that supplied the materials for projects such as the Louvre and Notre Dame were now directly (up to six storeys) below the sprawling city. 

[The Paris Metro's tunnels are only one part of the underground network]

The first major collapse happened in 1774. As time went on more and more holes opened up; swallowing neighborhoods and their inhabitants and exposing the voids in the city’s foundation. Stabilization efforts began during the reign of Louis XIV and continue to today as the Inspection Générale de Carrières (ICG) patrol the tunnels in search of weak spots in the network now spanning hundreds of miles. Ironically the ICG’s activities have expanded on the original network through the addition of a new labyrinth of maintenance access tunnels.  Inevitably, small collapses continue to occur with the largest of the recent past occurring in 1961 – killing 21 people.

[ICG Inspector at work. Photo: Stephen Alvarez for National Geographic, February 2011]

The voided space of this network was partially filled when Paris’ over-crowded cemeteries began to leak in the late 18th century, resulting in a public-sanitation emergency.  As a solution, the government brazenly began digging up the gravesites and transporting the remains to the former quarry locations.  After almost a century of this practice, over 6 million skeletons were displaced to these new catacombs.

[One of the many catacombs found underground]

Other somewhat unexpected official/permitted occupants of the network exist today:  There are the plump fish swimming in the 50 meter wide reservoir below Opéra de Paris Garnier and the opera staff who feed them.  The Paris police force trains their underwater skills in the very same water body.  The Banque de France built a vault 25 meters below ground in the 1920s.  The vault is estimated to hold 2,600 tons of the country’s gold reserves.

[Canal Saint-Martin]

The tunnels are accessed through entrances scattered across the city in places such as hospital basements, subway tunnels, church crypts and wine cellars of private residences; not to mention the thousands of manholes servicing the sewer system.  While many of these access points have been blocked off by the ICG and entering the underground was made illegal in 1955, an unauthorized population continues to occupy the tunnels.

[A UX workstation. Photo: UX via Wired Magazine]

On one hand there are the ‘cataphiles’ – urban explorers who value the spatial qualities of the space as well as the feelings of liberation from society’s rules.  On the other hand is the loosely formed collective known as les UX (for Urban eXperiment). While others appreciate the tunnels on their own terms, UX’s time in the underground is not spent wandering around but instead spent on improving some of Paris’ forgotten corners.  For UX, the catacombs are a means, not an end.  The group takes advantage of the highly connected network to infiltrate buildings from below and restore/repair valuable artifacts found above ground.  Most notably, a UX team, working covertly at night, repaired the Paris Pantheon’s clock – which, with UX’s efforts, chimed for the first time in 50 years on December 24, 2006.  Other improvements attributed to UX include restoring medieval crypts, building an underground cinema, and producing theatrical productions in monuments afterhours.  

One of the first articles written about the secretive collective was written by Jon Lackman for Wired Magazine in February 2012.  Neil Shea's article "Under Paris" and Stephen Alvarez's photographs in National Geographic (Feb 2011) are also great resources.