The next development was in 1000 BC , when china started making bronze and copper cowrie shells. It wasn't long before the chinese made round coins out of metal . The very first coins often had holes in them so that people could pass a piece of string through them to keep them together. By 500 BC metal coins had begun to appear in countries like persia and greece , and later in the roman empire. These were usually lumps of silver with the heads of various gods and emperors stamped on them to show they were real.