Using a reliable light-weight material as proof to pay on demand began during the Han Dynasty in 118 BC in China. No paper was available yet so they used leather. It is said the oldest known user of lightweight promissory notes was Carthage. They were known to have issued bank notes on parchment before the city was destroyed in 146 BC. In Europe, the idea of banknotes was introduced during the 13th century by explorers such as Marco Polo. This is a great page to find interesting banknotes from around the world. Take some time and do some exploring yourself!