sentences:  During the reign of King Sukjong, a monetary system of casting a variety of coins was established in the years 1097–1107.These coins included the 東國 (Dongguk "Eastern Country"), 海東 (Haedong "Eastern Sea") and 三韓 (Samhan "Three States") series of coins.Coins made from metals other than iron like copper and bronze were issued in the 10th and 11th centuries, but their circulation was limited.