COSA, an ancient city of Etruria, on the south-west coast of Italy, close to the Via Aurelia, 44m. E.S.E. of the modern town of Orbetello on a promontory above the sea. Evidence of the occu pation of the site in prehistoric times has recently come to light. When it became a Roman colony in 273 B.e., the town was strongly fortified and the walls, about a mile in circuit, with three gates, and seventeen projecting rectangular towers at intervals, are preserved in places to a height of over 3oft. on the outside, and 15 on the inside. Within the city no remains are visible. The place 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 was of some importance. In the 5th century we hear of it as deserted. There is a remarkable Etruscan cutting through the east end of the promontory, for the purpose of draining an adjacent lagoon_ See D. Levi in Studi Etruschi i. 477, and references.