The ring of walls, today a bit less than 3 kilometers, was constructed by the Etruscans around the end of the 5th century B.C. and can be seen at the base of the current day walls. It has a rectangular form with the two longer sides facing North and South and the shorter sides facing East and West. The short west side is very well preserved and the site of a recent reopening and restoration of the Etruscan gateway with unique double barrel-vaulted portals, which belongs to the Etruscan perimeter. The first part of the larger north side from Porta Santa Maria follows the course of the Etruscan perimeter until the area above Porta Colonia where it reveals a sewer spout which dates back to the time of construction of the original wall.