During the 20th century, following the introduction of reinforced concrete, many structural restorations were carried out on the built historical heritage using this material, which was often concealed into the ancient structures. Today it is necessary to know the real consistency of these structures, the seismic behavior and the state of conservation of the concrete and metal reinforcements. Instrumental investigations must be based on preliminary knowledge of the restorations carried out in the last century. Archive research is therefore essential to know the history of the restorations and identify the areas affected by the reinforcements, so as to carry out targeted diagnostic investigations and be able to effectively model the behavior of these mixed structures.