Welcome to one of the strangest places in Paris. It lies on the Left Bank, under the 14th arrondissement. Above you are ordinary streets, cafes and apartment buildings. Below them, in a network of tunnels and chambers, rest the remains of more than 6 million people. Here is the first thing to understand. This is not an ancient Roman burial place, whatever the name suggests. It dates from the late eighteenth century, and it began as a practical solution to a very urban problem: what do you do when a great city runs out of room for its dead? Paris answered by moving them below ground, into old stone quarries beneath the city. The route you will follow is only a small part of what lies beneath. The wider underground world is vast, and on the visit itself you walk a circuit of about one and a half kilometers. Over the next few minutes we will look at why the bones were brought here, how the move was carried out, and why a place built for sanitation became a site of remembrance that draws hundreds of thousands of visitors every year.