The coins known as Koson gold staters have been a mystery since the examples were found in the Transylvanian region, in the 16th century. There are two different but both widely accepted theories about the origin of the coins.
According to one theory, Koson staters were struck in 43 to 42 BC by Marcus Junius Brutus (assassin of Julius Caesar) from a treasure provided to him by the Roman Senate, for the purpose of raising an army to defend the Republic against forces loyal to the now-dead Julius Caesar. This theory generally assumes the KO??N inscription names a Dacian king, possibly Cotiso, whose troops Brutus may have hired.
The second theory which is relatively modern states that Koson staters were struck in either Dacia (modern Romania) or ancient Thrace (Northern Greece), possibly by the same King Cotiso or another King named Koson who was never mentioned by ancient historians. Though both the theories seem to be on-point, they have incomplete evidence and lack any historical records referring directly to these coins.
The Coson or Koson coins depict on the obverse three men bearing lictors walking right a consul framed by two fasces with green legend KOSON in the exergue inside a beaded border. The reverse depicts an eagle with its wings spread. He is perched on scepter, clenching a laurel wreath.
Image Courtesy: romaniancoins.org