Greek Imperial coins are Roman provincial coins issued in bronze and silver denominations, but never gold. The majority of the coins issued by the provincial mints were of bronze. Silver coins were common in regions of the Eastern Empire. In general Rome controlling the issue of silver coins, allowing the Roman government to influence events in the provinces. The coins issued by a city were used mostly by the inhabitants of that city in local transactions. When a new region was assimilated by Rome, the Romans would frequently allow the continuation of the original currency as a matter of expediency. Frequently, when a new colony was formed it would be given authority to mint bronze coins. These local coinages of the Roman Empire spanned more than three centuries from Augustus to Diocletian. There were over six hundred mints from Spain in the west to Mesopotamia in the east.

Greek Coin Book and Other References:

Mionnet = Mionnet, Theodore Edme Description De Medailles Antiques, Grecques Et Romaines
Imhoof = Imhoof-Blumer, von F    Kleinasiatische Münzen
RecGen = Waddington, William Henry    Recueil General des Monnaies Greques d'Asie Mineure
BMC = British Museum Catalogues
SNG = Volumes of the worldwide SNG project    Sylloge Nummorum Graecorum,
Moushmov = Moushmov, Nikola    Ancient Coins of the Balkan Peninsula
GIC = Sear, David R    Greek Imperial Coins & Their Values
RPC = Reinach & Hill    Roman Provincial Coinage
Varbanov = Varbanov, Ian    Greek Imperial Coins, Vols. 1-3
MacDonald = University of Glasgow    Catalogue of Greek Coins in the Hunterian Collection
WW = Wildwinds.com (reference & attribution site)