Prior to (and even during!) the use of coinage, the primary form of 'currency' was quite simply other goods. This system is called 'bartering' and it essentially worked like this: Say you are a grain farmer living in Crete, you would use a certain amount of your produce to feed your family and any surplus you had you would take to the market place and trade or 'barter' for other goods. Commonly in the ancient mediterranean societies the marketplace would contain scales & 'measures' which would allow you to weigh out your grain (or indeed any other commodity, metals etc) into standard amounts so they could be traded fairly (e.g. I'll give you 3 bucketfuls of grain for your bucket of pomegranates ).