Cosa, a city founded by the Romans after the defeat of the Etruscan cities of Vulci, rose above a rocky promontory which the Tombolo di Feniglia had linked, in a distant time, to the “island” of the Argentario.
At the foot of the promontory was built the port: Portus Cosanus, behind which could be found a large coastal lagoon, today called the Lake of Burano.
It later became a Byzantine fortress and mediaeval castle which was called Ansedonia, from which the resort takes its name.
Today it is possible to visit the ruins and the archaeological areas.
