In this article we present a new study of the Arch of Janus, analysing previously unpublished aspects of its architecture and chronology based on new data obtained from a recent research project. This study provides the first complete planimetric view of the monument, together with a stratigraphic reading of the structure, evaluating the different elements of spolia that were re-used in its construction. Also, the discovery of a new inscription that was re-used in building the arch finally confirms that it dates from the period of Constantius II (a.d. 357). Finally, we present a proposal for the reconstruction of the dedicatory inscription of the arch, preserved in the nearby church of San Giorgio al Velabro.
