sentences:  From the 17th century until the end of the 19th century, coins denominated in mun bearing the inscription Sang Pyeong Tong Bo (常平通寶) - the literal translation is "always exact coin" a reference to stable value - were the most widely circulated currency.The history of Korean currency dates back to around the 3rd century BC, when first coins in the form of knife coins, also known as "Myeongdojun" belonging to the state of Yan and Gojoseon; which were said to have been circulated.Grain coins were put to use within the kingdoms for a long period of time.