Diocese of Chiusi-Pienza
The former Italian Catholic Diocese of Chiusi-Pienza, in Tuscany, existed until 1986. In that year it was united into the Diocese of Montepulciano-Chiusi-Pienza. It was a suffragan of the archdiocese of Siena.
Catacombs are found at Chiusi. The martyrdom of the deacon Irenaeus and the virgin Mustiola probably took place under Valerian. The first known bishop was Florentius, present in 465 at the Roman synod under Pope Hilary. Ammiato Abbey was built by Ratchis, King of the Lombards, and afterwards rose to great power and influence.
Bishop Francesco degli Atti (1348) was a famous canonist. Chiusi formerly boasted of a famous relic, the betrothal ring of the Blessed Virgin, which was taken to Perugia about 1449 by an Augustinian friar; in consequence of this a war broke out between them, in which Perugia was victorious and remained in possession of the ring.