The Chiana [kjaːna] (Latin: Clanis) is a river in the Italian region of Tuscany. It is about 42 km long. It begins in the Apennines of Arezzo, runs through the valley of Chiusi, and flows to the inflow of Paglia just past where the Orvieto flows into the Tiber. Historically, they often caused substantial flooding in the valley of Clusium (Chiusi), which was felt even up to Rome. In the year 15 AD, it was suggested that it be part of the water in the Chiana Arnus (Arno). This project was abandoned because of opposition by the Florentines.
In the Middle Ages, the entire valley between Arezzo and Chiusi was an uninhabitable swamp, but towards the end of the 18th Century, the engineer Conte Fossombroni addressed the issue, and moved the watershed by about 25 km further south, so that water now flows partly into the Arno and partly into the Tiber.