Remnants of an early tower are incorporated into this post-war building. The tower stands approximately 9 meters, of which 2.5 meters are below ground level. This was one of the two site towers on the left while entering the city. Part of the oldest city walls that were 3500 meters in length and built between the 1st century B.C. and the 1st century A.D. The tower brickwork has mortar composed of pebbles. Several courses of large stone blocks are at the base. The finished exterior was octagonal on the outside and round on the inside.
The ancient gate that opened nearby, possibly with two arches, opened on to a bridge spanning the ditch surrounding the walls on the outside and connected with two main roads as it still does today. The name “Carrobbio” derives directly from the Latin quadrivium, meaning the junction of four roads.