A fear of disease-causing "miasmas" from rotting corpses lead to designating new cemeteries on the outskirts of Paris, in the fashion of the Greeks and Romans. These include Pere Lachaise. The fear of the stench from the mass grave of Saints Innocents lead to the removal of human remains and was performed on winter nights over a two year period, from 1785-1787.
These bones were placed in the Catacombes --named after the Roman catacombs, though these were simply abandoned quarries once populated by thieves--and were sorted and stacked neatly by type, just like in the Imperial City. The transfer of other urban cemeteries to the Catacombes occured until the 1870s; it currently hold the remains of six million Parisians. The Catacombs became a popular novelty for the old nobility who held dinner parties and picnics there.
In 1864, Haussmann and his team of engineers decided the best solution for the overcrowded cemeteries was mechanical: to develop one large cemetery for all of Paris at Mery-sur-Oise connected by a special railway. This funerary line would connect to the three other principal, overcrowded cemeteries: Napoleon I's Montmartre, Pere Lachaise and Montparnasse. As Saalman puts it, "Insensitive to the negative psychological overtones of his 'iron horse express to the grave' conception, Haussmann found himself unprepared for the popular outcry his proposal raised, and nothing became of it."
Nadar's photo-recreation of the emptying of urban cemetaries, 1861. The exposure required 20 minutes due to the lighting conditions so a mannequinwas used.