The ancient city of Cosa, situated on a small rocky promontory 114 meters
above sea level, was in historic times connected to the primitive island of Argentario by a thin strip of land referred to as the Tombolo di Feniglia.
Its foundation dates back to 273 B.C. in which it became a Roman colony after
the territory was conquered by the Consul Tiberius Coruncanio. The name Cosa itself derived from the ancient name "Cusi" or "Cusia", corresponding to a small Etruscan center established where Orbetello lies today.
It seems that Cosa was developed as a strategic point in the water in the middle
of the Tyrrheanian Sea since battles with Carthage were anticipated, thus its
location was not by chance.
The Romans, thanks to new military techniques acquired during the Samnite war and the campaigns of Pyrrhus, erected, also in Cosa, a mighty enclosed wall with three access ports to the city, which were constructed with enormous polygonal masses of limestone embedded between them; they also erected 17 square towers situated on the side facing the sea.
Also of interest is the water supply system, consisting of public and private tanks of which numerous traces remain in the whole urban area.