A hidden staircase found in an 800-year-old French church just led archaeologists to a 15th–16th century burial vault

Many times, there is much more to a historic building than meets the eye right under everyone’s feet. In the medieval stone walls of the Church of Saint Philibert in Dijon, France, what was meant to be a simple maintenance project ended up being a significant archaeological discovery. The floor of the church hid a secret that had been left out of any modern architectural plans.This discovery came about when workers were repairing the flooring. While doing so, they removed sections of the floor and concrete layer and found that there existed a vertical stone staircase that went straight into the ground below. The staircase opened directly to an underground burial chamber that was a late-medieval/early-modern burial vault.As the investigation continued, however, the scope of the discovery extended much farther than just that single room. This staircase turned out to be an access point into a stratified landscape, which consists of remnants and historical sites that shed light on more than one thousand years of the area.Exploring the unexpected structural stratification beneath the floorWhat prompted this unexpected discovery was not an attempt to explore any remains but structural issues concerning moisture retention and mineral accumulation. During the 1970s, a heated concrete floor was built inside the medieval church. However, this innovation led to a considerable amount of salt being trapped within the foundations, which had previously been utilised as a storage place for salt in the 18th and 19th centuries. The heating process caused these minerals to expand, thereby creating cracks in the structure.This field investigation was undertaken by the National Institute for Preventive Archaeological Research in France. Specialists compiled the exact technical information related to the site in the form of a report titled Sous les piliers de l’église Saint-Philibert de Dijon. While removing the concrete layer in a systematic manner, experts found an extensive series of graves.Within the core area of the church structure, researchers discovered a series of wooden coffins in the conventional east-west alignment pattern. In the course of their explorations of the main intersection, they came across a burial vault of the 15th-16th centuries, in which the bones had been carefully gathered and sorted in order to make room for future burials. Excavating the foundations of a medieval societyWhile field technicians cleared layers of dirt and debris, they discovered that the timeline of events at the site reached much further into the past than merely the construction of the 12th-century church. Under the layers of burials from the medieval period, the team found evidence of older graves, dating all the way back to the 11th century. Still more deeply buried, the excavation yielded six massive stone sarcophagi, constructed in the characteristic style of the Merovingian period.The overall architectural history of the site is explained in the previously referenced report. According to these findings, the team discovered the remains of yet another church structure that existed at this site in the 10th century. These remains were discovered by analysing the herringbone pattern used in the construction of this building, which is typical for early medieval structures.This finding marks another example of the tendency seen throughout European history, which is for the construction of new churches over old structures to ensure that the sacredness of the place is preserved and that stable foundations are used. Through uncovering these layers, the archaeological dig has allowed historians to see a vertical timeline of the development of the area from late antiquity through the medieval ages to the present day.