The paper presents the first results of the vibration-based Structural Health Monitoring strategy implemented on the historic Brivio bridge, within a joint research between Lombardy Region and Politecnico di Milano aimed at defining guidelines for the monitoring of key infrastructures. The bridge at study, dating back to 1917, crosses the Adda river and consists of three reinforced concrete tied arches. Due to its position, the Brivio bridge represents a crucial node for the vehicular traffic of the local road network. Firstly, documentary research, visual inspections, geometric survey, mechanical characterization of materials, and multiple dynamic tests are performed. The information collected on-site is then used to develop and calibrate a FE model of each arch. Once those preliminary activities are completed, a monitoring system is installed including 8 seismometers per span and 1 temperature sensor. The collected data are transferred in real time to a dedicated workstation and stored in separate files of 1 h, that are automatically processed using a multi-level procedure developed in the Matlab environment.