Beneath the feet of shoppers perusing the shelves of beauty products in a central Paris supermarket, archaeologists have been carefully dusting down hundreds of skeletons uncovered in a medieval mass grave.

The discovery, made during renovation work in the cellar of the Monoprix branch, has revealed what experts believe are victims of a sudden illness resembling an outbreak of Bubonic plague and could prove useful to historians studying burials in the Middle Ages.

Eight graves have so far been discovered, seven small plots and one much larger one in which 150 bodies have already been unearthed, but no one is yet sure how the bodies ended up beneath the store.

The supermarket stands on the site of the cemetery of the Trinity hospital, founded in the 12th century and destroyed at the end of the 18th, and experts say the organisation of the graves points to a mass mortality crisis.

Physical Anthropologist Marc Guillon said that the well-preserved skeletons hidden in the sand did not show any signs of a violent death, ruling out the possibility that it could be related to war.

It has to be a particular reason to have so many dead in a few days or a few hours and what is very, very important on these anatomical series is that there are no injuries on the bones. So its not a war event. We are sure about that, there is no injury, said Guillon, who works at the French National Institute for Preventative Archaeological Research (INRAP).

We have males, females, babies, kids, and that means that what happened to them happened all at the same time and touched all of the ages of this population from Paris in the Middle Ages. So it has to be an illness, he added.

Experts will carry out DNA testing and carbon dating to find out how the skeletons got there and archaeologists have until 20 March to dig and investigate, after which Monoprix can continue with its refurbishment work.