The effects of the ambient vibrations on the Colosseum, obtained during the experimental campaign carried out in June 2014 are reported in this paper. Data, which regard the basement and the external northern wall, were analyzed in both time and frequency domain. The vibration amplitudes at different locations were pointed out as well as the dynamic characteristics of the wall. The results obtained are the starting point for future extensive experimental measurements and monitoring. These are needed to plan a suitable preservation and retrofitting interventions. © 2017 International Society for Structural Health Monitoring of Intelligent Infrastrucure. All rights reserved.