Tunneling Into a Sealed Polish Crypt Reveals Six Coffins and a Mysterious Tar-and-Fabric Seal

Tunneling beneath a Polish monastery uncovers stacked coffins and an unusual tar-and-fabric seal

Archaeologists gained access to a sealed burial vault beneath the Church of St. John the Baptist and the Five Martyrs in Kazimierz Biskupi, Poland, after tunneling roughly 23 feet under the monastery complex. Using modern mining techniques, the team spent about a month reaching the subterranean chamber beneath the church’s altar.

Once inside, investigators found three stacked tiers of coffins—six individual burials in total. In one area the upper tier was separated from the coffin below by metal rods, a precaution the team believes indicates the person below was of particular importance.

“Such a layered sandwich of fabric and tar has never been encountered in any research, at least not in my own studies,” said Malgorzata Grupa of Nicolaus Copernicus University in Torun, according to the Polish Press Agency.

Of particular interest was an unexpected layer composed of fabric saturated with tar that appeared to seal at least one coffin. Tar has historically been used to seal coffins; the fabric layer may have enabled the application of additional tar or protected a coffin that was transported a long distance, suggesting a delayed interment or special handling.

The use of metal rods between tiers also drew attention. Researchers interpret this as a deliberate measure to avoid placing subsequent burials directly on top of a particular coffin—an indication that the lower burial may have been for a notable figure associated with the monastery or the local community.

Excavation is ongoing and careful conservation is required. Several coffins remain in situ while teams plan their removal: after the largest upper coffin is lifted, conservators will assess the preservation of the lower ones. Only after transfer to laboratory facilities will specialists be able to radiocarbon-date the remains, analyze any textiles or artifacts, and potentially identify who was buried there.

Work in the church’s vaults began in 2022, when researchers started to examine the remains of at least 100 people from dozens of coffins. The complex—built as a church and monastery between 1513 and 1520—is believed to contain the remains of Bernardine friars who owned the monastery, as well as local notables, with burials likely beginning in the 17th century.

Parts of the crypt that have been cleared will be opened to the public. Conservators plan to display artifacts recovered from the vaults—among them two women’s dresses, liturgical garments likely used in the church, and other clothing—while human remains will be respectfully reinterred in a side crypt.

What comes next

• Careful removal and conservation of the coffins and skeletons.
• Laboratory analysis to determine dates, preservation, and any personal or historical information.
• Public display of select textiles and liturgical items; reinterment of human remains in a side crypt.

Location: Kazimierz Biskupi, Poland. Significance: possible first documented instance of a fabric-and-tar sealing layer on a coffin and a clear example in Poland of metal rods used to protect a primary burial.