This week Neil MacGregor's history of the world is exploring the great empires of around 1500 - the threshold of the modern era. Today he is in Ming Dynasty China and with a surviving example of some of the world's first paper bank notes - what the Chinese called "flying cash". Neil explains how paper money comes about and considers the forces that underpinned its successes and failures. While the rest of the world was happily trading in coins that had an actual value in silver or gold, why did the Chinese risk the use of paper? This particular surviving note is made on mulberry bark, is much bigger than the notes of today and is dated 1375. The Governor of the Bank of England, Mervyn King, and the historian Timothy Brook look back over the history of paper money and what it takes to make it work. Producer: Anthony Denselow.