The need to eliminate Les Innocents gained urgency from May 31, 1780, when a basement wall in a property adjoining the cemetery collapsed under the weight of the mass grave behind it. The cemetery was closed to the public and all intra muros (Latin: “within the [city] walls”) burials were forbidden after 1780. The problem of what to do with the remains crowding intra muros cemeteries was still unresolved.
Mine consolidations were still occurring and the underground around the site of the 1777 collapse that had initiated the project had already become a series of stone and masonry inspection passageways that reinforced the streets above. The mine renovation and cemetery closures were both issues within the jurisdiction of the Police Prefect Police Lieutenant-General Alexandre Lenoir, who had been directly involved in the creation of a mine inspection service. Lenoir endorsed the idea of moving Parisian dead to the subterranean passageways that were renovated during 1782. After deciding to further renovate the “Tombe-Issoire” passageways for their future role as an underground sepulchre, the idea became law in late 1785.
A well within a walled property above one of the principal subterranean passageways was dug to receive Les Innocents’ unearthed remains, and the property itself was transformed into a sort of museum for all the headstones, sculptures and other artifacts recuperated from the former cemetery. Beginning from an opening ceremony on 7 April the same year, the route between Les Innocents and the “clos de la Tombe-Issoire” became a nightly procession of black cloth-covered wagons carrying the millions of Parisian dead. It would take two years to empty the majority of Paris’s cemeteries.
Cemeteries whose remains were moved to the Catacombs include Saints-Innocents (the largest by far with about 2 million buried over 600 years of operation), Saint-Étienne-des-Grès[better source needed] (one of the oldest), Madeleine Cemetery, Errancis Cemetery (used for the victims of the French Revolution), and Notre-Dame-des-Blancs-Manteaux. By this way the skeletal remains of several leaders of the French Revolution including Maximilien Robespierre and Georges Danton were transferred to the Catacombs.