 Human activity in the lands of modern Bulgaria can be traced back to the Paleolithic . Animal bones incised with man @-@ made markings from <unk> cave are assumed to be the earliest examples of symbolic behaviour in humans . Organised prehistoric societies in Bulgarian lands include the Neolithic <unk> culture , Vinča culture and the <unk> Varna culture ( fifth millennium BC ) . The latter is credited with inventing gold working and exploitation . Some of these first gold smelters produced the coins , weapons and jewellery of the Varna Necropolis treasure , the oldest in the world with an approximate age of over 6 @,@ 000 years . This site also offers insights for understanding the social hierarchy of the earliest European societies . 
