The Fortress Wall of Seoul (Hanja: 서울 漢陽都城; Hangul: 서울 한양도성;), or literally the Seoul City Wall is a series of walls made of stone, wood and other materials, built to protect the city of Seoul against invaders. The wall was first built in 1396 to defend and show the boundaries of the city, surrounding Hanyang (Hanja: 漢陽; Hangul: 한양 the old name for Seoul) in the Joseon Dynasty. At that time, it was called Hansung (Hanja: 漢城; Hangul: 한성). The wall stretches 18.6 km along the ridge of Seoul's four inner mountains, Bugaksan, Inwangsan, Naksan and Namsan. At present, a 12-km section of the wall is designated as Historic Site No. 10 (1963) and is protected accordingly, along with the gates, water gates, and signal fire mounds. The northern, eastern, and southern sections of Mt.Nam (Namsan section) walls have undergone extensive restoration work, having sustained damage or been entirely destroyed during Japanese imperial rule (1910–1945). Castellation In 1395, just five years after King Taejo founded the Joseon Dynasty, King Taejo established a government office [Doseongchukjoedogam (Hanja: 都城築造都監; Hangul: 도성축조도감)] to build a castle to defend Seoul. He ordered Jeong Do-jeon to search for and measure a site. On 1 January 1396 (by the lunar calendar), Taejo of Joseon held the groundbreaking ceremony. 197,400 young men were placed under civil conscription over two years and completed building the castle 98 days after the war along the mountains Bugaksan, Naksan, Namsan, and Inwangsan. The wall contained eight gates, all of which were originally constructed between 1396 and 1398. Characteristics The original walls, built in the late 14th century were constructed of medium-sized round stones held together by mud. During King Sejong the Great's reign in the mid-15th century, a large-scale refurbishment work was carried out on the wall, including the replacement of earthen wall sections with rectangular stone sections. A major restoration in 1704 by King Sukjong rebuilt sections of the wall using large, uniform stone slabs which mark the final and last unique characteristic of Hanyangdoseong. The eastern section of Seoul was on lower ground than the other sections and was more susceptible to external attack. Thus, a lookout was added to the outside of the gate to reinforce its defense. A part of the walls in the section between Heunginjimun and Gwanghuimun was extended outside in a rectangular shape for such a purpose. Signal fire mounds, another component of