COSA, an ancient city of Etruria, on the S.W. coast of Italy, close to the Via Aurelia, 4½ m. E.S.E. of the modern town of Orbetello. Apparently it was not an independent Etruscan town, but was founded as a colony by the Romans in the territory of the Volceientes, whom they had recently conquered, in 273 B.C. The town was strongly fortified, and the walls, about a mile in circuit, with three gates, and seventeen projecting rectangular towers at intervals, are in places preserved to a height of over 30 ft. on the outside, and 15 on the inside. The lower part is built of polygonal, the upper of rectangular, blocks, and the masonry is of equal fineness all through, so that a difference of date cannot be assumed; such a change of technique is not without parallel in Greece (F. Noack in Römische Mitteilungen, 1897, 194). Within the city no remains are visible. The place was of importance as a fortress; it was approached by a branch road which diverged from the Via Aurelia at the post station of Succosa, at the foot of the hill on which the town stood. The harbour, too, was of some importance. In the 5th century we hear of it as deserted, and in the 9th a town called Ansedonia took its place for a short time, but itself soon perished, though it has left its name to the ruins.
See G. Dennis, Cities and Cemeteries of Etruria (London, 1883), ii. 245. (T. As.)