Goryeo was the first Korean state to mint its own coins. Among the coins issued by Goryeo, such as the Dongguk Tongbo, Samhan Tongbo, and Haedong Tongbo, about a hundred variants are known. Coins failed to gain widespread use, whereas silver currencies were used until the end of Goryeo. In 996, Seongjong of Goryeo minted iron coins to trade with the Khitans, who used iron coins. The coins may have been issued to promote centralization. As far as can be established, the iron coins were not inscribed. The government made many efforts to promote the use of coins instead of commodity money.