The city of Karlovac is another fort from the times of the Military Frontier. It was built as a six-side star fort in the 16th century at the point of confluence of four rivers. The town blossomed in the 18th and the 19th century after being made a free town, with the development of roads between Pannonian plains to the seaside, and waterways along the Kupa river. The city is making use of its crucial geostrategic point in Croatia.