The recent discovery and excavation of the remains of a well preserved mold for bell casting below the floor of the medieval church of the SS. Trinità of Venosa (southern Italy) provides a singular opportunity to reconstruct aspects of ancient bell manufacturing technology and to compare the new archaeological data with the textual evidence on the same subject written by the famous monk Theophilus in the eleventh chapter of his treatise <i>De Diversis Artibus</i>. Stratigraphical excavation and video endoscopic inspection of the mold's interior allowed a preliminary reconstruction of the structure and use of this unique craft installation.