In 1333 Azzone Visconti, at the end of the period of wars that had led the lords of Milan to conquer definitely Monza, erected boundary walls of about 3 kilometres designed to protect the town centre. The walls were welded to the south around the great Visconti castle; today the only part left is the tower visible from Via Visconti. On the east side, to increase the protection, an artificial branch of the river Lambro was dug, the Lambretto. The moat starts just where the Ponte Nuovo, the most ancient practicable bridge still existing in town, was built. From the bridge it is possible to see the foundation of the medieval walls, demolished in the 19th century.