Alba Iulia (; or Carlsburg, formerly Weißenburg, , , Ottoman Turkish: Erdel Belgradi or Belgrad-i Erdel) is a city located on the Mures River in Alba County, Transylvania, Romania, with a population of 63,536 . Since the High Middle Ages, the city has been the seat of Transylvania's Roman Catholic diocese. Between 1541 and 1690 it was the capital of the Eastern Hungarian Kingdom and the latter Principality of Transylvania. Alba Iulia is historically important for Hungarians, Romanians and Transylvanian Saxons.