It is extremely difficult to check the effectiveness of upgrading on masonry structures, or more particularly, on monumental buildings, using traditional load tests which are generally neither feasible nor significant enough. This study proposes the use of a control system through dynamic tests that are capable of furnishing useful indications regarding the global stiffness of the structure being examined. The method has been tested on a part of the work upgrading done on the Colosseum in Rome. -- AATA