Using shallow geophysical methods to characterise the monumental building at the Segeda I site (Spain)

Abstract The Segeda I site is located in northeastern Spain and holds the remains of an important city mentioned in Roman sources on the conquest of the Iberian Peninsula, particularly the Celtiberian war, from 153 to 133 BC. Recent excavations at this site have revealed a peculiar structure outside the perimeter wall that can be related more to defensive or ritual functions than to production or domestic use. Several questions have arisen regarding the functionality of this unusual building. If it had been built for ritual purposes, a comparison with other sacred buildings would suggest the presence of foundation deposits or an inhumation urn. If it were a singular building, it would probably have a different constructive pattern and special foundations compared with the other constructions on the site. In order to investigate these two aspects, non-destructive geophysical methods have been applied to survey the buried inner parts of the building (architectonic target), and investigate the terrain under and around it (geologic target). A 2D-magnetic gradient survey was planned over the structure to locate possible foundation elements. 3D-laser scanner topography and 3D-ground penetrating radar (GPR) have been combined to ascertain the internal arrangement of ashlars and blocks. Finally, 2D-electrical resistivity tomography (ERT) profiles were performed to investigate the geological materials underneath the structure. The geophysical models obtained reveal the inner construction pattern and the siting of the structure.