CHIANA (anc. CLANIS), a river which rises in the Apennines south of Arezzo, runs through the valley of Chiusi, and after re ceiving the Paglia just below Orvieto, falls into the Tiber after a course of 6o miles. In Roman times it often caused floods in the valley of Clusium. In the middle ages the whole of its valley from Arezzo to Chiusi was an uninhabitable swamp ; but at the end of the 18th century the engineer, Count Fossombroni, moved the watershed some 25m. farther south, so its waters now flow partly into the Arno and partly into the Tiber.