Karlovac marks its birthday by commemorating 13 July 1579 when the building of the town started according to plans to construct a fortress in the form of a six-point star near the old town of Dubovac at the confluence of four rivers. It was originally known as Karlovec, Karlstadt, Carlstadt, or Carlstatt, named after Archduke Charles II of Austria, upon whose orders the construction began on 13 July 1579.