The sarcophagus is hidden beneath the floor of the Notre Dame Cathedral in Paris.
Archeologists were called in to help restore and conserve the cathedral after the devastating fire in 2019.
They discovered a human-shaped lead sarcophagus in preparation for the construction of the cathedral's spire.
CBS News reported that it was buried between the pipes of the heating system in the central nave.
According to the National Institute of Preventive Archaeological Research, the sarcophagus is in good condition despite some holes. The Daily Beast reported that it had buckled but remained sealed.
Archeologists believe it may be from the 14th century, but further research will help determine the identity of the person who died.
The archaeologists used a camera to look inside the casket. Cloth remains and organic matter were detected by the camera.
The contents of the sarcophagus are thought to be lined with wood from a boxwood tree.
NPR said boxwood trees were used to preserve the bodies of France's social elite.
It is an important character and could be found in the register of burials.
The coffin is thought to have been made for a church official in the 1300s.
According to The Guardian, the president of Inrap said that DNA tests will attempt to identify the dead person.
The sarcophagus containing a human body is not an archaeological object.
He said it was too early to say if the body would be reburied in the cathedral.
There is a secure location where the sarcophagus is currently stored. The Institute of Forensic Medicine will receive it for further research.
Archeologists discovered ancient tombs, a sculpture of a man's head, and a block from a rood screen during the excavation.