Boeun Samnyeonsanseong Fortress (보은 삼년산성)

Samnyeongsanseong Fortress was built during the Silla dynasty. The sprawling stone walls stretch 1.7 kilometers in length with x_heights and x_widths of 13-20 and 8-10 meters respectively. The name of the fortress comes from the time it took to complete the construction, three years ("sam nyeon" in Korean). The fortress was the site of many battles between Silla and Baekje during the Three Kingdoms Period.