If you are fascinated with ancient fortress and cities, must see for you is Krševica kale is located in south Serbia, near Vranje. It dates from 4th btc. Probably it is ancient city of Damastion, center of culture in time of Alexander The Great (Macedonian). It represent oldest settlement on Serbian territory. great Fortress and the city in time of ruling of Filip and Alexandar Macedonian was destroyed in 279btc, with invasion of Celts on this part of the Balkans.
Today many findings can be found in this locality, as this coin used for transaction in that time.
Photo of ancient coin of Damastion in Krševica kale