Starting from the left side fed into by the River Pioverna, we find the highest position occupied by Pennaso. Located along the road that leads to Valsassina, the town is known for its ancient gateway from which the Bellanesi people, with other neighboring populations, pushed back the soldiers of the Republic of San Marco. The fortification of the hamlet was once part of the wider fortified system of Lario and Valsassina. Within the early warning network from this point it was possible to communicate with the towers of Taceno and Sommo Incino, Assogno, Inesio and Bagnala. Scholars agree that the high strategic value of the site dates back to Roman times.