WATCH: Grisly Mass Graves Found Beneath a Supermarket

In the Monoprix supermarket in Paris, there is a door marked “staff only.” Through this door you can slip though a passageway, turn left and go down a spiral staircase into the basement. Here you’ll see the usual stock of juice and soda bottles, but if you go down yet another flight of stairs, there’s a mass grave with rows of medieval skeletons. There are 316 bodies in total.

Archeologists believe the mass grave is part of a cemetery of a hospital that used to stand nearby. The hospital was built outside Paris’s city limits in the early 13th Century and had served as a shelter for the poor and for pilgrims, a place of religious teaching that put on biblical plays, an infectious disease center and even a vocational school for children.

“There are babies, there are young children, there are teenagers, there are adults, men, women, elderly people,” Ms. Isabelle Abadie, an anthropologist and archeologist, said. “This was a mortality crisis, that much is clear.”

In the main pit, Abadie found 175 bodies neatly aligned next to one another. Those found in the other, smaller graves were jumbled together. She believes this is a sign, perhaps, of a rushed burial during an epidemic of some sort.

“It could be the plague, it could be a famine, it can be many things at this stage — but there are no traces of trauma, so these aren’t deaths linked to an act of violence or war,” she said.

The management of the Monoprix supermarket came upon this mass grave after deciding to renovate the store’s basement. That’s when workers came across long-forgotten cellars, and, underneath them, the skeletons.