The widespread use of spolia in post-ancient times in Rome reached its peak when St. Peter’s Basilica was newly constructed. The size and the significance of this large project provide an excellent basis for examining the use of spolia in Rome during the Renaissance period. Thanks to the archive that was established for the builders’ hut of St. Peter’s in the 16th century, written documents can prove the use of spolia and in addition allow us to name the places of their origin. In a bifocal approach, not only the spolia can be studied where they were reutilized but the deconstruction of ancient space can also be contemplated. In addition to the analysis of the spolia that were used when reconstructing St. Peter’s, 3D models help to distinguish ancient and spolia-column shafts in St. Peter’s and ancient buildings. Above all, the comparison of the entases between various columns leads to new and revealing insights.