Alba Iulia (Romanian pronunciation: [ˌalba ˈjuli.a]; German: Karlsburg, Carlsburg, formerly Weißenburg, Hungarian: Gyulafehérvár, Latin: Apulum in the Roman period, later Alba Iulia or Alba Yulia; Ottoman Turkish: Erdel Belgradı or Belgrad-ı Erdel) is a city located on the Mureş River in Alba County, Transylvania, Romania, with a population of 63,536 as of 2011. Since the High Middle Ages, the city has been the seat of Transylvania's Roman Catholic diocese.