Monitoring the Cathedral of Milan: An Archive with More Than 50 Years of Measurements

The paper describes the origin and evolution of the monitoring system of the Duomo di Milano, which was installed during the 1960s. In that period, differential movements induced by the extraction of groundwater (among other factors) caused significant instability and risk of collapse of the monument. Today, the monitoring system is still operative. Instruments, techniques, and calculation procedures were continuously updated considering the continuity of the time series, resulting in a precious archive for structural health monitoring and conservation. The actual configuration of the monitoring system includes a large variety of both automatic and manual sensors, digital and mechanical, in real-time or with an established periodicity. Moreover, the monitoring system inside the cathedral still preserves continuity with the original measurements thanks to continuous maintenance carried out over time. The manuscript illustrates and discusses the original system as well as the updates related to activities that began more than half a century ago.