 After the collapse of the Roman Empire (5th century AD), lack of maintenance of the irrigation systems associated with a cooling climate phase (i.e.the so-called Migration Period or The Dark Age Cold Period) led to the progressive waterlogging of the Po Valley and the natural depressions on the right side of the Po River turned in vast swamp basins.The waterlogging process of the area continued until the 10th century influencing the human sustenance and settling practices.