Chiusi was once one of the most powerful of the ancient cities of the Etruscan League, and it's now a valuable source of information about that archaic civilization. Fifth-century BC tombs found in the nearby hills have provided archaeologists with a wealth of artifacts. On the route of the ancient Via Cassia, Chiusi became a major Roman center and an important communication hub that linked Rome with the agriculturally
rich Chiana Valley to the east, with Siena to the northwest, and to other major cities in central and northern Italy. When the Chiana Valley became a malaria-ridden swamp during the Middle Ages, Chiusi's importance declined, and it was not until the Medici devised a scheme to drain the valley (with plans supplied by Leonardo da Vinci) in the early 15th century that the town began to reestablish itself.