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 kmeast of Izmir, the area is a UNESCOWorld Heritage Site because of itsmagnificentarchaeologicalremainsandthewhitetravertinepoolformationscreatedbyitspeculiargeothermal 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 surveyswere 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 wasmartyred.Ground-penetrating radar (GPR), electrical resistivity tomography (ERT) andmagnetic gradient investigationswere carried out in the central octagonal room, whereasthe accessiblelateral roomswere surveyedwith GPRand 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 threedimensional volumes (GPRand ERT) to allowan integrated interpretation of the geophysical results. Theanalysisof thegeophysicaldatasetsrevealeda seriesofanomaliesinboth the centralandlateral rooms that could be ascribed to the building foundations and to other possible archaeological structures, probablyrelatedtoearlierstagesofthesacredbuildingandto tombs, aswellasotheranomalies (voids, fractures) of presumable natural origin.