The development of coinage, beginning in Lydia around 600 BC, represents one of the most consequential economic innovations of antiquity. The introduction of state-guaranteed metal tokens of fixed weight and purity reduced transaction costs, enabled more complex commercial relationships, and created a new tool of political communication.

The Lydian electrum coins — a naturally occurring gold-silver alloy — were soon followed by the gold and silver coins of the Achaemenid Empire (the Daric and Siglos) and the silver coinage of Greek city-states. Athens' owls — silver tetradrachms from the Laurion mines featuring Athena's owl — became an international currency trusted across the Mediterranean world because of Athens' silver supply and commercial reach.

Coins functioned simultaneously as economic instruments and propaganda vehicles. The images stamped on them — deities, rulers, symbols of civic identity — were the most widely distributed visual media of the ancient world. Alexander's coinage showing him as a divine king spread his image from Egypt to India; Roman imperial coinage carried the emperor's portrait to the furthest reaches of the empire, making it the closest ancient equivalent to modern media.

The relationship between coinage and political legitimacy was direct: the right to coin money was a mark of sovereignty, and the debasement of coins — reducing their metal content — was both an economic act and a political statement about the issuing authority's reliability. Roman imperial coinage debasement in the 3rd century AD, when the silver content of the denarius fell from near-pure to effectively zero, contributed to the economic disruption of the Crisis of the Third Century.