Busosanseong Fortress, also known as Sabiseong or Soburiseong, was built to protect Sabi (present-day Buyeo), the last capital of Baekje (17 BC – 660). It is known to have been built in 538 when King Seong of Baekje was planning to move the capital of his kingdom from Ungjin (present-day Gongju) to Sabi. Some historians believe that the fortress already had a defensive wall enclosing a mountain peak before 500, and that it was reconstructed in 605 during the reign of King Mu of Baekje into the form we see today. The remaining features of the fortress show that it was originally intended to enclose the summit of Busosan Mountain and some of the valleys around it. The fortress also contains traces of its three main gates and a military depot as well as some historic buildings and sites including Nakhwaam Cliff, Sabiru and Yeongillu Pavilions, and Goransa Temple. Historians believe that the kings and aristocracy of Baekje used the fortress not only for military purposes but also, in times of peace, as a leisure park. The fortress is regarded as an important part of the Korean heritage both for its historic significance as the last stronghold of Baekje and witness to the kingdom’s fall, and for the presence of certain architectural elements that provide valuable information about the development of Korean fortresses.