Reconstructing the occurrence of diluvial storms over centennial to millennial time-scales allows forplacing the emergence of modern damaging hydrological events in a longer perspective to facilitate abetter understanding of their rate of return in the absence of significant anthropogenic climaticforcing. These extremes have implications for the risk offlooding in sub-regional river basins duringboth colder and warmer climate states. Here, we present thefirst homogeneous millennium-long(800–2018 CE)time-series of diluvial storms for the Po River Basin, northern Italy, which is also thelongest such time-series of monthly data for the entire Europe. The monthly reconstruction ofdamaging hydrological events derives from several types of historical documentary sources and reveals387 such events, allowing the construction of storm severity indices by transforming the informationinto a monthly, quantitative, record. A period of reduced diluvial storms occurred in the ninth andtenth centuries, followed by a stormier period culminating in the eleventh and thirteenth centuries.More complex patterns emerge in the fourteenth to sixteenth centuries, with generally wetter andstormier conditions than during other centuries. From the seventeenth century onwards the numberof damaging hydrological events decreases, with a return in recent decades to conditions similar tothose prior to the thirteenth century Theflood frequency tended to increase for all seasons duringperiods of low solar irradiance, suggesting the presence of solar-induced circulation changesresembling the negative phases of the Atlantic Multidecadal Variability as a controlling atmosphericmechanism.