## 3 Methodological Approach, Data Acquisition and Processing  
As a premise to the methodological approach used, it should be noted that the project of Eleftheria Square is a long-term plan that began in 2005 with its design and, today, its implementation is still ongoing. Furthermore, during the years the geophysical support was needed for the various purposes previously introduced, which cannot be separated from a case-by-case evaluation of the methodology to be adopted. Thus, the following workflow was considered:  
* Analysis of the needs of the investigation in collaboration with the technicians involved in the project, taking into consideration the typology of searched targets (archaeological remains, underground utilities, geological layers, cavities, water), their supposed depth (from centimeters to tens of meters), their constitutive material (stones, landfills, metal, plastic, fluids), their physical properties (density, conductivity, susceptibility) and their geometry (punctual targets, stretched objects, layers). * Evaluation of the geological stratigraphy of the area. It is composed by anthropogenic soils and fluvial deposits of different thickness overlying deep marl and sandy marl of the Nicosia Formation [56]. * Evaluation of the environmental noise of the study area considering the presence of metals, buried iron grids, anthropic buried artifacts and the occurrence of recent mechanical interventions. * Analysis of the typology of surfaces on which to operate (asphalt, concrete, paved areas, land) and the spaces available to work in. * Consideration of the differences in the operating principles and the applicability of the various geophysical survey techniques, taking into account the previous points. * Choice of the proper method that is suitable for solving the goal of the research. ERT, EMI and GPR were preferred over other methods. ERT, although having slower acquisition times and a small invasiveness due to the insertion of electrodes in the surfaces, was applied during surveys 1, 2 and 3 in order to obtain a good compromise between depth of investigation and resolution of results, features not achievable with EMI, GPR, seismic, magnetic and gravity methods. In addition, the presence of metals, energy lines and buried grids under paved surfaces during surveys 1 and 2 excluded the use of the expeditious technique such as the magnetic method and the GPR that have an extreme sensitivity to these environmental noises. GPR was used during survey 4 and 5 with the aim to produce high-resolution maps of shallow targets such as buried pipelines. Other methods, in this urban context, would not have led to a proper representation of them. EMI prospections were applied during survey 5 as they are very suitable for the identification of high conductivity bodies in a fast way as required by the research question. * Choice of the geophysical instruments to use during data acquisition. ERT was carried out using a multi-electrode resistivity meter, the A3000E (M.A.E. s.r.l., Frosolone, Italy). GPR was implemented through an IDS Georadar (IDS GeoRadar s.r.l., Pisa, Italy), equipped with a multi-frequency TRMF antenna (200-600 MHz), and a MALA X3M Ramac Georadar (Guideline Geo AB, Skolgatan, Sweden), equipped with a shielded 500 MHz antenna frequency. EMI prospections were conducted utilizing the GSSI Profiler EMP-400 [57]. * Definition of the parameters of acquisition taking into consideration the required depth of investigation and the resolution required by the research question. For ERT, profiles had different lengths, taking into account the available spaces in the different survey areas and the electrode spacing was in any case set to 1.2 m. Regarding archaeological prospections, the selected electrode spacing has been considered proper to reach supposed large deep walls. A dipole-dipole (DD) configuration was used.