This was once the Hongyemun (gate), placed along Cheonggyecheon 6-ga, specifically located below the castle wall towards Euljiro 6-ga from Dongdaemun. That gate was composed of five sections (in Korean, 5(o)-gan) thereby having the name of 'Ogansudari,' or 'Ogansumun.' This bridge was constructed on the passing point of Cheonggyecheon from castle town. To provide a smooth flow along the Cheonggyecheon, a five arch-hole bridge was constructed when the castle was installed. The castle wall was then built on those holes, and a bridge was set up by connecting the holes with Jangdaeseok (long, large stones). This Ogansunum was built to create a smooth flow, but it was also used for escape or going to castle town. During the Myeongjong Era, the Imggeokjeong group used to enter and exit castle town through this Ogansumun to destroy jails and quickly escape. The bridge was replaced by a concrete version after Ogansunum was destroyed in 1907 by Japanese Imperialists intent on destroying the castle. It has since been restored through the Cheonggyecheon Restoration Project.