close up view of the ramparts of belgrad fortres in serbia

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