The Dinaric mountain ranges of Lika and Gorski Kotar in the region's western reaches represent a natural barrier between the Adriatic Sea to its west and the Pannonian Basin and to its east, traversed by few high-performance transport routes until recently. The region was first spanned by a trading route between Senj and Pannonia in classical antiquity and later in Middle Ages, but the first modern road in the area was the Caroline road, completed in 1732 connecting Rijeka and Karlovac via Fužine, Mrkopalj, Ravna Gora and Vrbovsko, and named after Charles VI who ordered its construction. The same emperor commissioned construction of a narrow road between Karlobag and Gospić—the first to span Velebit. Those first roads were replaced by the more modern Josephina connecting Karlovac to Senj, largely tracing the Roman trading route across the Vratnik pass, and the Theresiana following a different route between Karlobag and Gospić, completed in 1779 and 1784 respectively. In 1789, a road to Dalmatia, branching from the Josephine road at Žuta Lokva towards Gračac via Gospić. Louisiana road was completed in 1809, also running between Rijeka and Karlovac, although via Delnice. The first railway built in the region was the Zagreb – Rijeka railway, completed in 1875. Since the 2000s, the region is spanned by modern motorways.