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 the issue of silver coinage was controlled by Rome. This was because by controlling the issue of silver coins, the Roman government could control and influence events in the provinces. The coins issued by a city were mostly used 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.