Seoksumun is a floodgate on the Dongnakcheon Stream, which flows through the town of Ganghwa-eup. The floodgate was built in 1711 (37th year of King Sukjong’s reign during the Joseon Period) and it is connected to the inner walls of the Ganghwasanseong Fortress. It is an arched structure with a design of three rainbows coming together. Made of granite, the floodgate measures 18.2 meters in length and 2.7 meters in x_height, while the arches are 1.7 meters tall, and 3 meters wide.