Greek Tetradrachms became the common monetary unit as a function of inflation and economic expansion in the Greek world. The early monetary system began with hemi-obol, obol, drachm, and a didrachm (2 drachms) in 545BC in Athens for example, there was a transition from didrachms to tetradrachms which occurred during c. 515–510 BC, which reflected the age of inflation. These coins are circulated and generally Very Fine. We have only a limited supply of these coins, which were the first One-World Currency in history. The same design was struck among all the cities conquered by Alexander. Each displays the mint mark of the city where they were struck.