Originally, the city was entirely surrounded by a massive circular stone wall to provide its citizens security from wild animals, thieves and attacks. The city has grown beyond those walls and although the wall no longer stands (except along Bugaksan Mountain (), north of the downtown area), the gates remain near the downtown district of Seoul, including most notably Sungnyemun (commonly known as Namdaemun) and Heunginjimun (commonly known as Dongdaemun). During the Joseon dynasty, the gates were opened and closed each day, accompanied by the ringing of large bells at the Bosingak belfry. In the late 19th century, after hundreds of years of isolation, Seoul opened its gates to foreigners and began to modernize. Seoul became the first city in East Asia to introduce electricity in the royal palace, built by the Edison Illuminating Company and a decade later Seoul also implemented electrical street lights.