The Arch of Constantine in Rome has recently undergone complete restoration. During restoration work surveys were also made in order to establish the static situation of the monument. This report gives the results of this research and attempts to show the validity and utility of the results obtained both through co-ordinated experiments - by relieving tension at certain points with the technique of flat jacks - and theoretically by accurate numerical models whose results, when compared with the experiments, enabled us to establish tensions over the entire monument and understand the causes of the present damage.