Fiat money is money that derives its value from government regulation or law. The term fiat currency is used when the fiat money is used as the main currency of the country. The term derives from the Latin fiat ("let it be done", "it shall be"). Fiat money originated in 11th century China, and its use became widespread during the Yuan and Ming dynasties. During the 13th century, Marco Polo described the fiat money of the Yuan Dynasty in his book The Travels of Marco Polo.