or ARNSBERG, a city of Westphalia, in Prussia, the chief town of a government and circle of the same name. It is situated on an eminence almost surrounded by the River Ruhr, 44 miles south-east of Munster, and 58 miles E.N.E. of Dusseldorf. It is the residence of the provincial authorities, and has a court of appeal, a catholic gymnasium, and a society of agriculture. Pop. 4438. Arnsberg was the capital of the ancient Duchy of Westphalia, and was formerly a member of the Hanseatic league. Near the town are the ruins of an ancient castle, once the residence of the earls of Arnsberg; the last of whom, Gottfried, sold his cardiom, in 1368, to the archbishop of Cologne.