 The largest remaining fragments of forest are located around the Ticino river and are protected by a Biosphere Reserve.The Po Valley has had traces of inhabitation since at least 780,000 years ago, when the first big glaciation of pleistocene took place.Sites like Monte Poggiolo may have served as refuges of human populations fleeing the terribly cold conditions of northern Europe during the subsequent glaciations along pleistocene 
The valley was covered by sea level in warm times, but glaciations could cause a lower sea level that allowed big mammals and humans to migrate from Africa and the Middle East to central and western Europe through an empty and open Po valley, avoiding the barrier of the Alps, reaching the Loire Valley, and Iberian Peninsula, and then, when glaciation retreated, the rest of continental Europe.