ARNSBERG, a city of Westphalia, in Prussia, the chief town of a government and circle of the same name, 51° 24' N. lat., 8° 7' E. long. It is situated on an eminence almost surrounded by the River Ruhr, 44 miles S.E. of Munster, and 58 miles E.N.E. of Dusseldorf. It is the seat of the provincial authorities, and has a court of appeal, a Catholic gymnasium, which was formerly the Benedictine abbey of Weddinghausen, a library, a normal seminary, and a society of agriculture. Weaving, brewing, and distilling are carried on, and there are manufactories of white lead, shot, and paper, as well as works for the production of railway plant. Arnsberg was the capital of the ancient duchy of Westphalia (incorporated with Hesse Darmstadt in 1803, and with Prussia in 1816), and was a member of the Hanseatic league. The new part of the town has been built since 1815. Population in 1873, 5123. 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 earldom in 1368 to the archbishop of Cologne.