Keren Su / CORBIS

Paper bills were first used by the Chinese, who started carrying folding money during the Tang Dynasty (A.D. 618-907)  mostly in the form of privately issued bills of credit or exchange notes  and used it for more than 500 years before the practice began to catch on in Europe in the 17th century. While it took another century or two for paper money to spread to the rest of the world, China was already going through a fairly advanced financial crisis: the production of paper notes had grown until their value plummeted, prompting inflation to soar. As a result, China eliminated paper money entirely in 1455 and wouldn't adopt it again for several hundred years. Another not-so-well-known fact: the word cash was originally used to describe the type of round bronze coins with square holes commonly used in the Tang Dynasty, called kai-yuans.