(CNN) Archaeologists in France have unearthed the extraordinarily well-preserved corpse of a 17th-century noblewoman -- still dressed in her dress, bonnet and shoes.
A team from the French National Institute for Preventive Archaeological Research discovered the body when they pried open her lead coffin during a rescue excavation on the construction site of a new conference center in Rennes in northwestern France.
"When we opened the coffin (we) saw a body, a lot of volume of fabric, the shoes," said anthropologist Rozenn Colleter, who is part of the team. "We didn't know how well-preserved she was until we scanned her."
Colleter describes her as a "natural mummy -- particularly well preserved."
Inscriptions allowed the archaeologists to identify the nearly intact body as belonging to Louise de Quengo, Lady of Brefeillac, who died in 1656.
Louise was buried in a cape, serge wool dress and plain shirt and leather mules with cork soles. Her face was covered with a shroud, two bonnets and a hood.
Her lead coffin was first opened in March 2014. It was one of five -- among approximately 800 graves -- found at the site, which has housed the Convent of the Jacobins since the 12th century.
A lead reliquary containing the heart of her husband, Toussaint de Perrien, Knight of Brefeillac who died in 1649 was also discovered nearby.
Once the coffin was open, the team had to rush to preserve her body.
A unique set of circumstances had preserved the corpse for hundreds of years, but it was not embalmed so they knew decomposition would start rapidly.
"We had only a few days to work," said Colleter.
They collaborated with scientists from the Molecular Anthropology and Synthetic Imaging Laboratory at the University of Toulouse to scan the entire body.
They also collected samples of uncontaminated human tissue and DNA and pathogens including tuberculosis.
Samples could help researchers looking for a cure of tuberculosis, said Colleter.
From analysis, the scientists concluded that Louise de Quengo died from an infection.
"It's extraordinary," said Colleter of finding such a well-preserved corpse. "You have to have a lead coffin, but it has to be (hermetically sealed), without insects and the humidity has to be low.
"The doctors said the body was like (one) that has been buried for two weeks, but she is 350."
Louise de Quengo will be reburied once all the scientific tests are completed.