GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 3.2 667 The EtruscanWell in Perugia. Perugia is the capital city of the Umbria region (central Italy) and it is located on a top of a hill made of fluvial and lacustrine deposits dated to middle and upper Pleistocene. The top of the hill, where the downtown is settled (Fig. 1a), has been inhabited since the X – XI cent. B.C., but the Etruscan people were the first real civilization present in Perugia. In the historic center several notable evidences of this illustrious past are present. Between these, the Etruscan Well is one of the most remarkable feats of hydraulic engineering referred to the Etruscan civilization in the 3rd century B.C. (Fig. 1b). The cylindrical well has a diameter of about 5.6 m for the first 12 m of depth, then narrowing to a diameter of about 3 m and reaching a depth of approximately 37 m (Fig. 1c). The unusual size of the well, bigger compared to other similar etruscan ones, has been interpreted as a cistern only later transformed into a well to reach a deep-water table. Actually, the well was fed by three springs of water, but the water level is ensured under the ground surface due to a continuous pumping system; this makes us hypothesize a system of artesian level in the subsoil. Archeological studies (Stopponi, 1973; 1991) and evidences along the perimeter wall of the well suggest the presence of a tunnel deriving from the well and elongated below the Piccinino square, where the well is located. For the validation of these theories, a geophysical investigation was carried out on May 13, 2019. We have performed a Ground Penetrating Radar (GPR) survey (Jol, 2009), successfully used in previous archeological studies in this region (Ercoli et al. , 2012; Ercoli et al. , 2016). Through such geophysical data, it was possible to study the structure of the well inside the Piccinino square complex, and infer possible hypotheses regarding structures connected to it. Fig. 1 - Study site; a) location of the city of Perugia (red dot) in the Tiber Basin (yellow area) of the Umbria region; b) position of the Etruscan Well (Pozzo Etrusco) in the city center (Piazza Piccinino); a section of the well displaying its geometry (from www.pozzoetrusco.it ). Ground Penetrating Radar survey. The GPR survey was planned and based on a three dimensions structural model of the well, formerly obtained by a team of geologists and engineers using geomatic techniques. The GPR data have been collected using a Zond-12e GPR Advanced (http://www.radsys.lv/en/index/ Latvia) equipped with a 500 MHz antenna. The survey grid at the Piccinino square was designed using metric strings; an odometer connected to the antenna was used to record a GPR trace every 0,02 meters. The GPR grid encompassed eighty N-S profiles spaced 0.5 meters (Fig. 2a), having variable length due to surface obstacles and buildings located in the square. Once completed the acquisition of the main grid, additional