 Following the corridor is Ugo's one, having, on the ceiling, prisoners' writing done with candle smoke.Before 1385, since at least one hundred years, on the site where the Castle of Saint Michael was built, an old watchtower stood to defend the northern line of the city walls and, more exactly, the near strategic gate called of the Lion, beyond which a small homonymous district extended.A large canal, that flew into the river Po with its tributaries, defended the northern stretch of walls.