CHIANA (anc. Clanis)  , a river of Tuscany, which rises in the Apennines S. of Arezzo, runs through the valley of Chiusi, and after receiving the Paglia just below Orvieto, falls into the Tiber after a course of 6o m . In Roman times its waters ran entirely into the Tiber . It often caused considerable floods in the valley of Clusium (Chiusi) which were noticeable even in Rome itself, and in A.D . 15 it was proposed to divert part of its waters into the Arnus, a project which was abandoned owing to the opposition of the Florentines (Tac . Ann. i . 76, 79) . In the middle ages the whole of its valley from Arezzo to Chiusi was an uninhabitable swamp; but at the end of the '8th century the engineer Count Fossombroni took the matter in hand, and moved the watershed some 25 M. farther south, so that its waters now flow partly into the Arno and partly into the Tiber .