L'Ossuaire Municipal in Paris holds the bones of about 6 million people. A small part of the 321 km long tunnel network has been a popular tourist attraction since 1874, but this subterranean museum was not exactly planned as being one. Rather, two threats for the city of Paris made it inevitable to create that what we know as the Catacombs of Paris today.
To explore the history of the catacombs, we have to travel way back to the first century, when Paris was occupied by the Romans and still called Lutetia. The Romans found there was limestone in the soil of the left bank of the river Seine, which is of perfect use for building walls. Up until the High Middle Ages, the limestone was acquired in open quarries outside the city walls. Then, in the 12th century, mining was replaced to underground workings. This had several advantages: deeper deposits could so be reached, and on surface level the soil could still be used for agriculture. When the city continued to grow in the 16th and 17th century, new underground quarries were developed and the old quarries were abandoned. Buildings, streets and neighborhoods of the expanding city were built over the quarries, that subsequently fell into oblivion.
But not for long. The Parisians again became aware of the existence of these underground galleries when houses and streets started to collapse in the late 18th century. These collapses were the result of the cave-in of the roofs of the 30 meter deep subterranean galleries, resulting in a chain reaction within the different layers of soil. The crumbling worked its way upwards and resulted in a collapse of the buildings on street level.
The most catastrophic collapse of this kind occurred in 1774 in the Rue D'Enfer, which ironically means 'Hell's street'. Indeed, the cavity which measured 30 meter in length as well as in depth reminded of a gaping entrance to hell. Pavements, buildings, even carriages and horses were swallowed by the gap. The limestone from the houses' walls returned to where it had come from.
Since the mining galleries where everywhere beneath the city, Paris was threatened to be go under completely...
Cimetière des Innocents
At the same time, something else was threatening the citizens of Paris: their ancestors. Whereas the Romans buried their people outside the city walls, the Franks built cemeteries in the very center of the city. In the 12th century, the most central and at the same time the city's principal cemetery was the Cimetière des Innocents, which was located adjacent to the Les Halles marketplace.
The site had begun as a regular burial site with individual or family tombs, but it grew to be a site for mass graves already a century after its establishment. This didn't, however, avoid that the cemetery was soon overflowing. To make place for new graves, older bones were exhumed and stored in the inside of the cemetery walls.
In spite of diseases and famines, the Parisian population kept growing, and so did the number of dead. The cemetery did by far not have the capacity for that number, and thus bodies had to be exhumed very early, resulting in the excavating of bodies that were not even completely decayed. The smell of the decomposing bodies poisoned the air in such a way that it made milk turn sour. Since the cemetery was located in the middle of the city, people living adjacent to the burial site suffered extremely. In 1779, direct neighbors suffocated by the stink. At that time, the burial ground was so overflowed that it was more than two meters over the normal street level. In 1780, the wall of an adjoining basement collapsed by the weight of the mass grave and the cemetery was finally closed for public. It is estimated that Les Innocents was the final resting place of about two million Parisians during the six centuries between its establishment in the 1130s and its closure.
Two problems turn to be each other's solution
Now we come back to the quarry problem. After the collapse in the Rue d'Enfer, King Louis XVI had ordered the mapping of all tunnels and caves underneath Paris. The architect Charles-Axel Guillaumot was hired to inspect and map all the quarries. Soon it was discovered that there was a second, underground city underneath Paris. For orientation, he named the tunnels to the streets above them. Next, Guillaumot erected pillars in the galleries to consolidate the tunnels in order to avoid further collapses. Also, he dug perpendicular passage ways between galleries that were wide enough, resulting in a giant network of interconnected tunnels. The renovated tunnels happened to be the perfect place to keep the massive amount of bones from the Saint-Innocents cemetery. And thus an evacuation was arranged in 1785.
The limestone quarries in the Montrouge area, now in the 14th arrondissement, were chosen to become the location for what was then baptized Les Catacombes de Paris, named after the Catacombe di Roma. Interestingly, the entrance to the Catacombs is located in the Place D'Enfer. In other words, the entrance to the Catacombs was built in the street that had collapsed in 1774! Despite the memory of this infernal collapse, the underground area was sanctified and so prepared to become a gigantic underground mass grave, and the evacuation was started in 1785. Since the dead were to be treated with highest respect, the transportation from Les Innocents was carried out as a holy ceremony. Starting at nightfall, the carts carrying the bones were accompanied by torchbearers and priests chanting the Requiem continuously. It would take fifteen months before all bones were moved. In due course, the bones from all other Parisian cemeteries were removed and stored in the Catacombs as well, which made the nightly transportation ritual continue until 1814. Place D'Enfer changed its name in the late 19th century and is now called Place Denfert-Rochereau. Please note the phonetic similarity of D'Enfer and Denfert. The street shall always be reminded as being the gate to hell...
In 1810, the skulls and bones (mostly femurs) were stacked in nice patterns and figures. Tablets displaying from which cemetery the bones had come from were accompanied by poetic verses. The new quarry inspector advertised the existence of the Catacombs, and soon curious Parisians were drawn down into the colossal ossuary. Initially, only guided excursions were offered, but they soon became a major tourist attraction - and still every year, hundreds of thousands visitors descend into the Catacombs to look at the centuries old bones.