When silver money was struck, it was natural that the barter-unit which came nearest in value to the silver didrachm would be equated to it, and the piece of silver would accordingly be termed Shield or Tortoise, just as the silver equivalent for the old copper rod was called the Obol, and in due course the corresponding device would be impressed on the silver coinage. The same explanation may probably be applied in other cases, such as that of the boar on the coins of Lycia. On the coins of the Gaulish tribe Sequani who made the best bacon and hams which came into the Roman market, the swine is found44. Doubtless this animal was their chief source of wealth, and formed a unit of barter, but we have not space for any more examples.
It is worth noting that it is quite possible that the men who issued the earliest coins of Boeotia and Aegina were influenced in the shape they gave these coins by the actual objects which they were replacing. The coins of Aegina with their high round upper side and flat under side suggest the general outline of a