As with the Thasos Dionysos coins, the Romans imitated them, paid them to Thracian mercenaries for services rendered or as a bribe not to cause trouble, the locals loved them so much that they copied them themselves. Some coins they didn't seem to copy much was Aesillas and Athens NewStyle. The experts are Evgeni Paunov and Illya Propakov and ,of course, the usual duo, Andrew Meadows and Francoise DeCallatay-all on academia.edu.