During the Etruscan era, Chiusi became one of the main cities in the whole Etruscan city network; in the 6th century BC, the town began to form its first contacts with Rome. It was at this time, towards the end of the 6th century BC, that the Etruscan King Porsenna laid siege to Rome and probably conquered it. Chiusi’s wealth was particularly tied to its immensely fertile alluvial soil and the city’s strategic position along an important commercial route. Heading up the Tiber river through the Chiana valley, which was navigable at the time, the route led right to the Valdarno.
After having been seized by the Goths in 540 AD, Chiusi became home to a Lombard Duchy, known to have existed until 776. From the 11th century onwards, the city’s power remained firmly in the hands of its bishop; by the following century, however, it had to submit first to the rule of Orvieto, then that of Siena. In this period, the commune of Chiusi was established, though it was later annexed by the Republic of Siena.