The ox became a universal unit of exchange in antiquity; it was employed as the basis of evaluation for all currencies. A 25.5 gram copper ingot , or 8.5 grams of gold, equalled one whole ox. The Greek historian Herodotus tells us the Lydians invented coins, which eventually replaced ingots and bars because coins were easier to transport. Initially the Greeks imprinted familial coats of arms on their coins; later, as rulers of city-states took control of minting, their arms became the symbol of the city-state itself. Very often the design on the coat of arms was determined by a particular deity with which the city-state had an affinity. For example, periodically throughout its history the city-state of Athens minted owl coins which was decorated on the obverse of the coin with the head of Athena, the patron goddess of Athens, and on the reverse with the owl, associated with her worship. Other Greek symbols on coins included animals or plants which typified a certain region. Until the Hellenistic period images of monarchs and great men were never depicted on Greek coins. We regularly add to our Greek coins stock; please re-visit soon.