Clusium (the modern Chiusi), one of the twelve cities of the ancient Etruscan confederation, situated on the right bank of the Chmis, near a small lake to which it gave name, and 83 m. N. N. W. of Rome. Virgil mentions it among the cities which assisted AEneas against Turnus. Its original name is said to have been Camars. Under the rule of Porsena, about 500 B. C, it espoused the cause of the Tarquins, and in conjunction with other Etruscan states laid siege to Rome, which is supposed by modern critics to have surrendered, and submitted to humiliating conditions of peace. But the final issue of the war seems to have been unfavorable to the Etruscans, though how or when is not certainly known. During the later wars of the Romans with the Etruscans we hear of the Clusians only once, and then in conjunction with the Perusians, who were enemies of Rome. At what time Clusium passed under the dominion of the Romans is unknown. In 295 B. C. a Roman legion stationed at Clusium was cut to pieces by the Gauls. The latter in their third great invasion, 225 B. C, appeared under the walls of Clusium shortly before their decisive defeat at Telamon. In the second Punic war Clusium was under Roman rule, and furnished Scipio with corn and timber for his fleet.

In the civil wars of Sulla and Marius the Clusians sided with the partisans of Marius, who were twice defeated near the city. Under the empire Clusium seems to have received a fresh colony of citizens, who enjoyed separate rights, and are mentioned as Clusii novi, in distinction from the Clusii ve-teres. But few remains exist of the former greatness of the city. (See Cniusi.)