Holstein, former duchy, N central Germany, the part of Schleswig-Holstein S of the Eider River. Kiel and Rendsburg were the chief cities. For a description of Holstein and for its history after 1814, see Schleswig-Holstein. For a time part of the duchy of Saxony, Holstein was created (1111) a county of the Holy Roman Empire and was bestowed on Adolf of Schauenburg. In 1459, Holstein's Christian I, a Danish heir to the throne, established a personal union with Denmark, to the great displeasure of the German majority. In 1474, Emperor Frederick III raised Holstein to a duchy under the immediate suzerainty of the Holy Roman Empire (as distinct from Schleswig, which was outside the imperial jurisdiction).