Cosa was a Latin colonia founded under Roman influence in southwestern Tuscany in 273 BC, perhaps on land confiscated from the Etruscans (Velleius Paterculus 1.14.7; Livy Periochae 14; Strabo 5.2.8). The Etruscan site may have been where modern Orbetello stands; a fortification wall in polygonal masonry at Orbetello's lagoon may be in phase with the walls of Cosa. The position of Cosa is distinct, rising some 113 meters above sea level and is sited 139 km. northwest of Rome on the Tyrrhenian Sea coast, on a hill now known as Ansedonia.