Eumseong Mangyisanseong(望夷山城, Mangyi mountain fortress) is located on the Mountain Mayi(馬耳山, an elevation of 472 meters). This article examines the historical background of Mangyisanseong and its operation in ancient and medieval times through literature materials. Mangyisanseong was under the jurisdiction of Gukwonseong(國原城) or Gaechasangun(皆次山郡) in Goguryeo, Gukwonsogyeong(國原小京)ㆍJungwongyeong(中原京) or Gaesangun(介山郡) in Silla, and Juksan(竹山) or Chungju(忠州) in the early Goryeo. After that, it was under the jurisdiction of Chungju until late Joseon. Mangyisanseong was first built by Baekje. It is generally understood that the fortress was operated as Baekje advanced south into the Chungcheongbuk-do region after the fourth century, and Goguryeo's southward advance to the Han River increased its military importance after the late fourth century. In the middle of the fifth century, Goguryeo occupied the Namhan River basin centered on Chungju, and it belonged to Goguryeo’s territory until the middle of the sixth century. Then, after Silla advanced towards Han River basin in the middle of the sixth century, it was operated on the traffic routes leading to Chupungnyeong Route(秋酒嶺路), Gyerimnyeong Route(鷄立嶺路), and Jungnyeong Route(竹嶺路). During the Goryeo period, Mangyisanseong was related to Gwangjudo(廣州道) and Pyeonggudo(平丘道) among the 22 Yeokdo(22驛道, 22 stations of the Goryeo). The main stations in the Chungcheongbuk-do region led to Gyerimnyeong Route and Chupungnyeong Route and were connected to Jungnyeong Route. Mangyisanseong was in the southern part of Gyeonggi-do, connecting major stations in the Chungcheongbuk-do region. Therefore, it was operated on a traffic route leading to those three routes. A beacon system was operated in Mangyisanseong during Joseon Dynasty, and it was also located at a key point. Located on the beacon route connecting Eumseong-Chungju and Cheongju of Chungcheongbuk-do, it received beacon from various places of Chungcheongbuk-do and delivered it to Anseong, Gyeonggi-do. Mangyisanseong was not only a strategic point during the time when the three kingdoms were competing, but also a key point for traffic routes and beacon routes from Unified Silla to the medieval times.