Carlsburg, Or Karlsbnrg(Hun. Karoly-Fejer-vd)'), a fortified town of Transylvania, on the Maros, 44 m. S. of Klausenburg; pop. in 1870, exclusive of the garrison, 7,955. It consists of . the upper town or citadel, built on a hill, and surrounded by walls with seven bastions, and the lower town beneath. The principal gate of the citadel is adorned with fine sculptures. It is the residence of the Roman Catholic bishop of Transylvania and of a bishop of the United Greek church, and has a cathedral containing the tombs of many historical persons, two convents, a theological seminary, a gymnasium, an observatory, a mint, several libraries, an arsenal, a hospital, and several schools. From the lower town there is a bridge over the Maros. There are mines of gold in the vicinity. The town was originally called Weissenburg (Lat. Alba Julia; Hun. Gyula-Fejervar), and received its present name from Charles VI. It was devastated by the Tartars in 1241, and rebuilt about a century later. In 1849 it was successfully defended by the Austrians against Gen. Bern.