GPR, ERT and magnetic investigations inside the Martyrium of St Philip, Hierapolis, Turkey

Hierapolis, Denizli, Turkey, was one of the most important Hellenistic-Roman cities in Asia Minor. Located about 250 km east of Izmir, the area is a UNESCO World Heritage Site because of its magnificent archaeological remains and the white travertine pool formations created by its peculiar geothermal setting. The Italian Archaeological Mission in more than 50 years of activity in Hierapolis has brought to light and restored important vestiges of the ancient city, helping to understand the urban layout in the various epochs of its development. In 2001–2003 geophysical surveys were performed by the University of Lecce in several areas inside the archaeological site of Hierapolis to support the archaeological excavations. This paper reports the results of the integrated geophysical surveys performed in 2003 inside the Martyrium of Saint Philip, a mausoleum built on the place where it is believed that the Apostle was martyred. Ground-penetrating radar (GPR), electrical resistivity tomography (ERT) and magnetic gradient investigations were carried out in the central octagonal room, whereas the accessible lateral rooms were surveyed with GPR and occasionally ERT. The acquisition was performed along a series of closely spaced lines and the processed data were visualized as two-dimensional vertical sections (GPR), map view (magnetic gradiometry), depth slices or three-dimensional volumes (GPR and ERT) to allow an integrated interpretation of the geophysical results. The analysis of the geophysical datasets revealed a series of anomalies in both the central and lateral rooms that could be ascribed to the building foundations and to other possible archaeological structures, probably related to earlier stages of the sacred building and to tombs, as well as other anomalies (voids, fractures) of presumable natural origin. Copyright © 2009 John Wiley & Sons, Ltd.