The paper presents an overview of diagnostic campaigns carried out to assess the state of conservation of two Frescos named “Agaso’s Fresco” (case study A) and “The flower garden Fresco dedicated to the deceased Savinianus” (case study B) at the St. Alexander Catacombs in Rome’s. The activity was developed within the COBRA project, which focuses on disseminating and transferring ENEA advanced instruments, IT services, innovative technologies to SMEs working in the field of cultural heritage protection and conservation. Due to narrow space of access to the case study A, situated in a critical area of the Catacombs, the photogrammetric survey was the only technique capable to perform a complete rendering of the entire element after its restoration. However, three different technologies were applied on the case study B: photogrammetric 3D reconstruction, acoustic imaging test and the thermographic survey. The results of the above-mentioned technologies on case study B have been aligned, compared and fully integrated in order to detect critical areas of the fresco in terms of detachments, cracks and structural weakness. In particular, photogrammetric reconstruction allowed overlying the experimental results obtained by acoustic imaging measurements and thermographic survey to fix their exact position with a great accuracy. The comparison and the integration between these technologies is a useful way for monitoring the state of preservation of archaeological finds, in order to integrate experimental data coming from different diagnostic instruments.