Archaeologists set to work excavating the site at the Convent of the Jacobins in Rennes, France in 2014. The site contained roughly 800 graves and five coffins—one of which contained a surprising discovery.

When they pried open the fifth coffin, the team found the well-preserved, 350-year-old body of noblewoman Louise de Quengo. The remains were so securely intact that the body was still fully clothed in a wool dress, cape, bonnet, and shoes.

Perhaps even more remarkably, the team was able to identify the body because of inscriptions on a nearby lead reliquary containing the heart of her husband, Toussaint de Perrien, Knight of Brefeillac, who died in 1649. De Quengo died a few years later in 1656. She was in her 60s.

While the hermetically sealed coffin kept the body well-maintained for hundreds of years, the team knew that state would begin to deteriorate immediately in the open air.

Archaeologist Rozenn Colleter, of the National Institute for Preventative Archaeological Research, told The Guardian, “But we had to move quickly because once the coffin was opened it sets off the decomposition process again after 350 years. We had 72 hours to bring the body down to four degrees to preserve everything.”

An autopsy showed De Quengo had kidney stones and “lung adhesions,” and scientists believed she died from an infection. Her heart, like her husband's, had been removed.

De Quengo was later reburied in Rennes.