6th century BC. Group comprising: cast 'coins' or currency pieces in the form of a bifacial dolphin. Sear 1684. 13.55 grams total. ("). This unique type of coinage was cast in Olbia, in the Black Sea area of Thrace from the 5th to 3rd century BC; there are many varieties; the casting method employed was adopted by the Gallic Celts who originally came from this area; the dolphins were generally cast in a tree form connected by the tail, although some examples seem to have been cast individually.