"They've prepared a small hole for you," the inspector says, holding the van door. He grins. "You're going to suffer!" He slides the door shut.
We rattle down a quiet avenue on a warm spring morning. Men and women walk to work beneath the deep green canopies of the chestnuts. In the suburb of Arcueil the driver pulls over on a busy street. At the roadside his colleagues are slipping into blue coveralls and tall rubber boots, putting on helmets. We join them at a manhole beneath an ivy-covered embankment. A dark shaft falls away at our feet.
One by one the members of the team switch on their headlamps and step down the ladder. They are from the Inspection Générale des Carrières, the IGC. It is their job to make sure Paris doesn't collapse into the quarries that riddle its foundations. At the bottom of the ladder we squat in a narrow passage, while Anne-Marie Leparmentier, a geologist, measures the oxygen level. Today there is plenty.
We head off into the passage, bent over like trolls under the low ceiling. The limestone walls sweat, and water sloshes around our boots. Fossils of sea creatures peel out of the stone, and in a slick of mud we find a rusty horseshoe—a relic from an animal that worked down here more than a century ago, hauling stones.
Modern Paris sits atop massive formations of limestone and gypsum. The Romans were the first to harvest the stone; their bathhouses, sculptures, and arena can still be found on the Île de la Cité and in the Latin Quarter. Over the centuries, as Roman Lutetia became Paris, quarrymen burrowed deeper and wider, carving out the stuff of the city's great buildings—the Louvre, for example, and Notre Dame. Open pits evolved into networks of underground galleries.
In the beginning the quarries lay far beyond the city limits. But as the city grew, parts of it sprawled directly above old tunnels. This progression happened over generations and without oversight. Quarrymen labored in an unregulated world of torchlight, choking dust, and crushing accidents. When they exhausted a quarry, they stuffed it with rubble or simply abandoned it. At the surface, no one paid much attention. No one realized how porous the foundations of Paris had become.
The first major collapse occurred in December 1774, when an unstable tunnel crumbled, swallowing houses and people along what is now the Avenue Denfert-Rochereau. More holes opened over the next few years, sending more houses tumbling into darkness. King Louis XVI commissioned an architect named Charles Axel Guillaumot to explore, map, and stabilize the quarries. Slowly teams of inspectors worked through them, shoring them up. To make their job easier they dug more tunnels to connect the isolated networks. Around the same time, when the king decided to close and empty one of the city's packed, putrefying cemeteries, Guillaumot was asked to put the bones somewhere—and so some Parisian quarries became the catacombs.
Today Leparmentier and her team continue the work of Guillaumot's first inspectors. Nearly a hundred feet below the street, we pause before a pillar, a stack of five or six boulders from the early 1800s. "Don't touch," Leparmentier says. "It's a bit fragile." A large black crack bisects the ceiling the pillar is still holding up.
Small collapses still happen every year, she tells me; as recently as 1961, the earth swallowed an entire neighborhood in the southern suburbs, killing 21 people. Leparmentier makes some notes. Another tunnel runs beneath us. She makes a plunging motion with her hand. Someday this pillar might fail, and the tunnel we stand in may collapse into the one below it.
We go deeper. At the end of a corridor we sit and contemplate the small dark hole I was warned of hours before. It's barely as wide as my shoulders. No one is sure where it goes. A young member of the team stuffs himself into the hole, his legs kicking the air. I glance at Leparmentier, and she shakes her head, as if to say, No way am I going in there. But she also waves her hand: Be my guest.