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a river in northwestern Italy, a right tributary of the Po River. The Tanaro is 276 km long and drains an area of about 8,000 sq km. It rises in the Maritime Alps and flows through the highlands of Monferrato. The lower course crosses the western part of the Po-Venetian Plain. The mean flow rate of the lower course is 116 cu m per sec. The river is used for irrigation. The cities of Asti and Alessandria are on the Tanaro.