Successively governed by the Roman, Byzantine, Ottoman Empires, and later a part of communist Yugoslavia, modern Serbia is a veritable amalgam of European cultural history.  In Belgrade’s old city, Stari Grad, visit the ancient Belgrade Fortress, built in 535 BCE on the confluence of the Danube and Sava Rivers, Republic Square, and the Church of Saint Sava, one of the largest Orthodox churches in the world. Continue your Serbia tour and head to picturesque Fruška National Park, the jewel of Serbia, or visit surrounding vineyards.  Nicknamed Gibraltar of the Danube, Petrovaradin Fortress looms on the east bank of the river in the city of Novi Sad. In the south, Niš Fortress is one of the best-preserved fortress in the Balkans, and dates to the Ottoman Empire.