In 540 AD it was occupied by the Ostrogoths and was later seat of Lombard duchy. From the 11th century it was under the rule of the local bishop, and was later contended by Orvieto and, from 1231, Siena, belonging to the latter until 1556, when it was annexed to the Grand duchy of Tuscany.
The lowlands around Chiusi are a treasure trove of tombs for this civilization. The Etruscan Museum of Chiusi is one of the most important repositories of Etruscan remains in Italy.
Other sights include:
The Romanesque Cathedral (Duomo) of San Secondiano, built around 560 AD over a pre-existing basilica, and renovated in the 13th century. It has a nave and two aisles supported by antique columns. The Sacrament Chapel houses a Nativity and Saints by Bernardino Fugai. It has a separated bell tower which was turned into a defence tower in 1585. Under the tower is a Roman swim pool dating from the 1st century BC.
The so-called "Labyrinth of Porsenna", a series of tunnels under the town, built in the 6th-5th century BC and probably utilized in Etruscan-Roman times for drainage of rain waters. According to Pliny the Elder (Naturalis historia, XXXVI, XIX, 91-93), the Labyrinth was part of a monument including the sepulchre of the King Porsenna.