At the southern part of the medieval village, at the confluence of the Verde stream and the Magra river, we find the entrance of the low village at the bridge of “San Francesco di Sotto”. The tower of the Seratti, by an old noble family of Pontremoli, or called of the Casotto as well, by the name of an elegant house, was erected to its defense in the XIV century. The door and the tower make part of the structure inner strucutre of Pontremoli, defended from the natural environment between the two water courses and from the Piagnaro castle to the north.