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. A few hundred years later leather was used as money in China, and in 806 AD the first paper banknotes were produced by the Chinese. It was still many years before paper currency appeared in Europe. Three centuries passed before it was used in all European countries