Beneath an unmarked cellar door in a 15th century church lies a dark, secret, osteological oddity.

Leuk is a small town in Switzerland’s Rhone Valley mostly known for the thermal spa to the north, but the town itself has been around a very, very long time. The first church was built around the 6th century out of a preexisting Roman building. This was torn down and reconstructed several times before the gothic St. Stephan’s Church was erected in 1494.

In 1981 the church undertook a restoration project. The restorers pulled up the floorboards with the intention of building a basement community center, but soon found that would be impossible. A hidden cellar had been housing a 9-foot-tall, 65-foot-long wall of skulls for centuries.

During archaeological excavation the very next year, 26 statues were discovered hidden beneath three feet of bones. They were dated between the 13th and the 16th centuries, around the time the current church building was constructed. The artworks found in the charnel house included a remarkable Pièta and a well-preserved Danse Macabre fresco, still on view in the charnel house. Its memento mori inscription reads: “What you are, we once were. What we are, you will become.”

No one is quite sure why the charnel house is there, or why it was kept secret. Some historians speculate that these many bones didn’t end up beneath the church via war, disease, famine or disaster, but rather there simply wasn’t enough room in the cemetery for them. Some of the skulls have what appear to be bullet wounds, which may mean that they were victims of a 1798 battle, exhumed from the cemetery after it became overfull.

Whatever the case, the discovery enlivened the city. Several medieval buildings in Leuk were in ruins and slated for demolition. When the secret ossuary beneath St. Stephan’s was discovered, renewed interest in the old buildings increased. They have now been restored, and serve as another draw to the historic little town.