Chiani
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 from this valley now flows partly into the Arno and partly into the Tiber . 
<triplet> Arezzo <subj> Arno <obj> located in or next to body of water