aerial view of belgrad fortress kalemegdan, historic walls and bastions at the confluence of danube and sava

ancient architecture attraction balkan battlefield belgrad castle belgrade beograd beogradska building capital city danube europe fort fortification fortified fortress historic history kalemegdan kula nebojsa landmark medieval monument nandorfehervar octagon old protection red roof ruins sava serbia serbian sightseeing stone stronghold sun tourism tower town travel tvrdjava wall walls yugoslav yugoslavia