grren wall and icon of church of the holy mother of god crkva ruzica in belgrade fortress or beogradska tvrdjava

archeological architecture balkan battlefield belgrade beograd beogradska building capital caste castle city danube europe fort fortification fortified fortress garden gate green hill historic historical history kalemegdan landmark leaf medieval monument nature nobody observation outdoor park river ruzica serbia serbian sightseeing stone stream stronghold tourism tower travel tvrdjava wall walls