Hidden beneath "The City of Light" is a dark underworld, the final resting place of more than six million Parisians. The Catacombs of Paris are underground ossuaries formed of a network of tunnels, caves, and quarries filled with mortal remains, where the former citizens of Paris now form a part of its foundation. As Paris went on its way to becoming an important hub, thousands flocked to the city. This spurred justified concerns about the limited cemetery space, leading to the creation of the catacombs in 1810 at the site of the old Montrouge stone quarries. Although in use as an ossuary as early as the 1780s, it was not until this time that the catacombs were organized. The bones were arranged as per the cemeteries they were taken from, creating a subterranean skeletal world, where the last of the lot were brought down in 1860. During World War II, this network of galleries was used as a hideaway for the Résistance movement; its vastness and the discretion of its entrances were great assets indeed. These ossuaries, illustrated by texts, create a chilling atmosphere and describe some of the defining events in the history of Paris, giving visitors substance for meditation. It is also occasionally used as a macabre venue for concerts, parties and other events.