The Catacombs of Paris are underground ossuaries in Paris, France, which hold the remains of more than six million people. Built to consolidate Paris's ancient stone quarries, they extend south from the Barrière d'Enfer former city gate; the ossuary was created as part of the effort to eliminate the effects of the city's overflowing cemeteries. Preparation work began shortly after a 1774 series of basement wall collapses around the Holy Innocents' Cemetery added a sense of urgency to the cemetery-eliminating measure, and from 1786, nightly processions of covered wagons transferred remains from most of Paris's cemeteries to a mine shaft opened near the Rue de la Tombe-Issoire.

An ossuary is a chest, box, building, well, or site made to serve as the final resting place of human skeletal remains. They are frequently used where burial space is scarce. A body is first buried in a temporary grave, then after some years the skeletal remains are removed and placed in an ossuary. The greatly reduced space taken up by an ossuary means that it is possible to store the remains of many more people in a single tomb than possible in coffins. The practice is sometimes known as grave recycling.