It's 1780 in Paris, and the heavy spring rains are saturating the earth.
In a home near the center of town.
A basement wall collapses under the pressure, releasing a flood of decomposing corpses remains from the neighboring Cemetery of the Innocents.
Rumors spread that everyone in the house got sick due to bad air emanating from the decaying flesh.
With the overcrowded cemetery housing generations of dead Parisians, there was a growing worry that the entire city was in grave danger of falling ill.
For centuries Parisians had buried their dead in the Innocence, the city's largest cemetery.
While cemeteries across Europe were originally placed outside of urban areas, in the 9th century the church began allowing burials directly on its grounds.
As these urban parish cemeteries filled, some churches started creating bone chapels, like the Sedlec ossuary in the Czech Republic, to make room for new burials.
By the 18th century, public opinion on urban cemeteries shifted as enlightenment thinkers and physicians promoted new scientific ideas that linked hygiene to health.
They didn't yet understand the concept of germs, believing instead that disease spread through miasma or bad air.
Consequently, overcrowded cemeteries spewing cadaverous odors were cast as public health threats.
Even after the Innocents and other cemeteries closed in the early 1780s, Residents continued to worry about the foul smells and petitioned the government for a long-term solution.
But where could they move the remains of the millions of Parisians?
The vast, abandoned network of quarries beneath the city offered a logical solution.
Dating back to Roman times, the mines had provided the limestone and plaster to build Paris.
But by the 18th century they had begun collapsing under the city's weight, creating deadly sinkholes.
So, in 1777, King Louis XVI established a team of engineers to survey and reinforce the area.
And in 1785, Charles Axel Guy L'Hommeau, the Inspector General of Quarries, was tasked with turning sections of the unused tunnels into a massive crypt.
The Catholic Church initially resisted as it stood to lose income from burials and cemetery maintenance fees, but public health concerns prevailed.
The transfer of human remains was done mostly at night to avoid upsetting passers-by and to limit public exposure to the miasma.
Millions of anonymous bones were dug up by hand, carted across Paris and dumped unceremoniously in the catacombs.
It was a distinctly modern project, focused on efficiency rather than memorialization.
The Cemetery of the Innocents was the largest source, though bones were soon brought from cemeteries throughout the city.
The French Revolution temporarily stalled relocation efforts.
Though the catacombs did offer a space where inconvenient bodies could disappear, some of the over thousand prisoners executed in the revolution's September massacres of 1792 were hastily cast there.
However, the catacombs weren't generally used for new burials.
Instead, the newly dead were interred in garden cemeteries established once again on the city's outskirts.
By the end of the revolution, the relocation project had sprung back to life and, in 1809, Napoleon Bonaparte, aware of the unifying power of monuments, ordered that a small section of the chaotic space be curated and open to the public.
Piles of bones were pushed to the sides, facades of skulls and femurs were artfully arranged and quotes about the fleeting nature of life were hung on the walls.
The rest of the catacombs housing the remains of an estimated six million Parisians was, and largely remains, untouched.
After its beautification, the catacombs became a hugely popular tourist destination.
While signs indicated the cemetery where the bones were moved from, the remains themselves were anonymous.
Aristocrats lay next to neighbourers, raiders next to defenders, the young next to their elders.
And so the site became a symbol of what one 19th century photographer called the confused equality of death.
Sources vary, but some say the last remains were moved as recently as the 1930s.
Today, people from around the world continue to visit the catacombs, finding amidst its caverns a haunting reminder of our shared, inevitable future.
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