I. Or Saxe-Altenburg, a sovereign duchy of the German empire, bounded by Prussia, Saxony, Weimar, Meiningen, Rudolstadt, and Reuss-Gera, the last of which divides it into two parts, the E. division constituting Alten-burg proper and the W. Saal-Eisenberg; area, 510 sq. m.; pop. in 1871, 142,122. It is traversed by spurs of the Erzgebirge, and in the west by ridges of the Thuringian Forest. The principal rivers are the Pleisse and the Saale. The duchy contains several large lakes and mineral springs, extensive forests in the west, and coal mines in the east. It is among the richest in Germany in agricultural products, especially in rye and wheat; a great many cattle are raised, and the horse and sheep are of superior breed. Wild boars and deer abound. The manufactures are leather, woollen cloths, hosiery, linen goods, wooden wares, and brandy. The duchy joined the North German confederation in 1866, where it had one vote, which it also has in the empire. The local legislature or diet consists of one chamber with 30 members. The present duke, Ernest, who succeeded his father in 1853, is a general in the Prussian and a major general in the Saxon army. In former times the duchy belonged to the Osterland, and was ruled by the margraves of Pleissen. In 1803 it was divided into two principalities.

In 1826 it assumed its present territorial form. The inhabitants are chiefly Wends by descent, and many in the rural districts retain the antique costumes. II A city, capital of the preceding duchy, situated on the Pleisse, 24 m. by railway S. of Leipsic; pop. in 1871, 19,966. It is well built, and contains many churches, a museum of painting and statuary, a gymnasium, and a great number of educational and literary institutions. The most celebrated public building is the palace, situated on an escarped rock. Altenburg has manufactories of cigars, gloves, brushes, and haberdashery, and an important book trade. It was for some time an imperial city. In 1430 it was almost destroyed by the Hussites.