The aim of this study is the characterization of a pre-Trajan wall structure decorated with mosaics and located below the Cryptoporticus of the ÒBaths of Trajanî complex in Rome. The surveyed wall is 15 m large and 0.9 m wide, with an height ranging from 3 to 5 m. Ground Penetrating Radar (GPR) and Seismic Refraction Tomography profiles were performed on the wall for reconstructing its inner geometry as well as characterizing its building materials, with the additional purposes of mapping fractures and evaluating seismic velocities of materials, to give safety indications before restarting the excavation. The wall was surveyed with horizontal and vertical massive GPR profiles and with two seismic lines. Both the seismic lines and the GPR profiles are able to detect the discontinuity between the two different materials forming the wall, confirming the consistency of the joint interpretation of the two different non-invasive techniques. Moreover they allowed us to locate weak materials and fractures. These results will be used for planning a safety project for the future archaeological excavations. We demonstrate that this approach constitutes an important tool for the characterization of the current status of an archaeological wall.