Below Paris’ 12million residents lay the remains of 6 million others – known as France’s Empire of the Dead, a world which is brought to life in a new documentary on CNN.
The Paris catacombs are a 200-mile network of old caves, tunnels and quarries and much of it is filled with the skulls and bones of the dead.
Much of the catacombs are out of bounds to the public, making it illegal to explore unsupervised.
But nevertheless, it is a powerful draw for a hardcore group of explorers with a thirst for adventure.
A tourist-friendly, legal entrance can be found off Place Denfert-Rochereau in the 14th arrondissement of Paris, near the Montparnasse district.
Here, visitors from all over the world can descend into the city’s dark and dank bowels for a whistle-stop tour of a small section of the catacombs.
One visitor told CNN: “I think people are fascinated with death. They don’t know what it’s about and you see all these bones stacked up, and the people that have come before us, and it’s fascinating. We’re trying to find our past and it’s crazy and gruesome and fun all at the same time.”
The well-worn trail might be enough to satisfy the tourists, but other Parisians like to go further – and deeper – to explore the network.
The name given to the group of explorers who go into the cave network illegally and unsupervised is Cataphiles.
The top secret groups go deep underground, using hidden entrances all over the city. And they sometimes stay for days at a time, equipped with head lamps and home-made maps.
Street names are etched into the walls to help explorers navigate their way around the underground version of the city and some groups have even been known to throw parties in the tunnels or drink wine.
For catacomb devotees, the silence experienced deep in tunnels cannot be replicated anywhere else.
Urban explorer Loic Antoine-Gambeaud told CNN: “I think it’s in the collective imagination. Everybody knows that there is something below Paris; that something goes on that’s mysterious. But I don’t think many people have even an idea of what the underground is like.”
Those caught exploring unauthorized sections of the network could end up out of pocket. Police tasked with patrolling the tunnels have the power to hand out fines of 60 Euros to anyone caught illegally roaming the network.
A by-product of the early development of Paris, the catacombs were subterranean quarries which were established as limestone was extracted deep underground to build the city above.
However, a number of streets collapsed as the quarries weakened parts of the city’s foundations. Repairs and reinforcements were made and the network went through several transformations throughout history.
However it wasn’t until the 18th century that the catacombs became known as the Empire of the Dead when they became the solution to overcrowding in the city’s cemeteries.