 Among the Greeks, coins in actual burials are sometimes also a danakē (δανάκη) or other relatively small-denomination gold, silver, bronze or copper coin in local use.In Roman literary sources the coin is usually bronze or copper.From the 6th to the 4th centuries BC in the Black Sea region, low-value coins depicting arrowheads or dolphins were in use mainly for the purpose of "local exchange and to serve as ‘Charon’s obol.‘" The payment is sometimes specified with a term for "boat fare" (in Greek "naulon", ναῦλον, Latin "naulum"); "fee for ferrying" ("porthmeion", πορθμήϊον or πορθμεῖον); or "waterway toll" (Latin "portorium").