Analysing the invisible: GPR survey at the Church of the Holy Sepulchre in Jerusalem

The Church of the Holy Sepulchre in Jerusalem, undoubtedly the symbol par excellence of Christianity, is the primary Christian pilgrimage destination since its creation in the fourth century. It has preserved its historical, religious, cultural, tangible and intangible values until today. Being a ‘Living Religious Heritage’ under the custody of the Christian communities, the Church underwent several transformations over the centuries following historical, natural and accidental events, leading to the current structure of the Basilica. At the beginning of the third millennium, planning for restoration interventions was set out by the Christian communities; initially, renovation of the aedicule (the Tomb of Christ). Subsequently, a feasibility study aimed at restoration of the entire floor of the Church was carried out by an interdisciplinary team that planned technical and scientific surveys to document the present state of the floor and the underground situation. Some geophysical surveys were undertaken on the shared spaces per the status quo rules to investigate the presence of buried archaeological structures and more recent technical facilities. The ground penetrating radar (GPR) method was used with good results for the depth of bedrock under the floor, thickness of the ashlars, the presence of ancient buried structures and cavities (channels, walls, and paving roads), and the water contents of the soil layers. These are visualised in 3D virtual excavations.