City of Mulheim an der Ruhr, North Rhine Westphalia Land ‏(state)‏, western Germany. It lies just southwest of Essen, in the Ruhr industrial region. First mentioned in 1093, it was early associated with the counts von Broich, whose medieval castle still overlooks the city. It later belonged to the duchy of Berg, with which it passed to Prussia in 1814. It was chartered in 1808. Between 1878 and 1929 Mülheim absorbed a number of neighbouring towns, including Broich and Heissen. Mülheim is a hub of rail and road traffic and a Rhine-Ruhr river port. Heavy industry includes iron foundries, blast furnaces, tube and rolling mills, and machine works. There are also chemical and electrical industries. Mülheim was formerly an important coal-mining centre. Historic buildings include St. Peter's Church ‏(11th century; now completely rebuilt)‏, Styrum Castle and the former Cistercian convent of Saarn ‏(both 13th century)‏, and the house of Gerhard Tersteegen ‏(died 1769)‏, a pious braid maker and hymn writer. Well-planned modern sections of the city were constructed after World War II, and there are many open-air recreational facilities, including the Raffelberg racecourse and spa. The Max Planck Institute for Coal Research is where the Fischer-Tropsch process for liquefying coal and the Ziegler process for the production of polyethylene plastics were discovered. The Max Planck Institute for Bioinorganic Chemistry is also in Mülheim. An art museum in the city features 20th-century German art. Pop. ‏(2003 est.)‏ 170,745.