Andernach (änˈdərnäkh) [key], city (1994 pop. 29,650), Rhineland-Palatinate, W Germany, a port on the Rhine River. Its manufactures include chemicals, metals, synthetic fibers and related products, and construction materials. Drusus founded a Roman frontier garrison there about A.D. 12. In 939 at Andernach, Emperor Otto I defeated the rebellious dukes Geselbert of Lotharingia and Eberhard of Franconia. From 1167 to 1801 the city belonged to the archbishopric of Cologne. In 1815 it passed to Prussia. Andernach has a Romanesque church (13th cent.), a 16th-century town hall, and parts of its medieval city wall.