Subsurface geophysics applied to archaeological investigation of Thabudeos Roman fortress (Biskra,Algeria)

Tahouda, former Roman Thabudeos, is situated 400 km south of Algiers (Algeria). It is one of the fortresses belonging to Roman south defense line in North Africa. This region is archaeologically very poorly known except for surface remains. The geophysical survey formed part of a wider research project designed to record and assess the landscape context of the longest Roman defense line in North Africa. We present the geophysical mapping and imaging using electric resistivity tomography and electromagnetics to help in investigating the subsurface properties of the region. Data were obtained using: (1) Saris resistance meter with up to 25 electrodes spaced at 2 m intervals and lines up to 50 m long. A total of 11 lines was obtained. (2) Geonics EM31, in two dipole configuration modes with 16 lines up to 100 m sampled every meter. These methods prove to be very powerful tools to give insight and locate the anthropologic remains from the surface to a depth of 6 m and outline their geometry. The results obtained by the two methods are consistent above the main remains like walls and rooms.