Inside the Sarcophagus: Non-Destructive Testing of a Medieval Tomb in the Cathedral of Bamberg (Germany)

In recent years, digital technologies have become increasingly prevalent in the field of heritage protection. In addition to geomatic techniques like laser scanning (LiDAR) and Structure-from-Motion (SfM), geophysical methods, especially Ground-Penetrating Radar (GPR), offer added value for investigating protected buildings and objects. Additionally, chemical analysis (e.g., X-ray fluorescence, XRF) and mineral magnetic methods can be utilized to investigate specific research topics. All these methods are completely non-invasive and leave the heritage site untouched. Furthermore, they are cost-efficient and fast to use. Within this paper, we want to present an integrated study of a medieval sarcophagus in Bamberg Cathedral. The geophysical surveys via GPR and magnetic susceptibility (MS) measurements should answer open questions regarding the construction and internal layout of the sandstone sarcophagus, dated to the Early or High Middle Ages. The susceptibility data indicated an inner lead coffin in the lower part behind the stone slabs due to an unusual diamagnetic response in these parts. In contrast, the GPR data gave no such indication and revealed that the interior is too small for a direct burial of the bishop. Hence, an additional XRF survey was conducted to help solve this contradiction. The latter data indicate that the lead could be due to remains of a former painting on the sarcophagus with colours containing lead white pigments. Due to the porous sandstone, the moist environmental conditions, and the high weight of the lead elements, these could have accumulated at the bottom of the sarcophagus, creating the diamagnetism detected by the magnetic susceptibility measurements.