Orbetello was a thriving Etruscan centre as of the 7th century B.C., though the city seems to have been abandoned in the 5th century B.C. At the time it was refounded, in the 4th century B.C., the massive walls were built, several ample segments of which are still visible today. The walls are one of the best preserved examples of a polygonal construction, an ancient architectural technique that contemplated the use of large blocks of rough-hewn stone (sandstone in the case of Orbetello).

In the points where the nearness of the sea would have rendered the ground unstable, special stockades of oak and pine trunks were erected to block the level on which the walls would rise. A second stockade was built in front to assure against the risk of possible landslides.