Chiusi (kyōō´sē), Lat. Clusium, Etruscan Chamars, town (1991 pop. 9,103), in Tuscany, central Italy, in the Apennines. Chiusi was one of the 12 sovereign towns of ancient Etruria; its semilegendary king Lars Porsena is said to have marched from there against Rome (c.500 BC). The town was taken by Rome (c.225 BC). Many Etruscan ruins have been found, including tombs dating from the 5th cent. BC, and there is an excellent Etruscan museum. There are also Christian catacombs.