It was the Battle of Samnyeon fortress, which located in Boeun county of Chungbuk province, in 928 that had been only to fail among the combats that Goryeo Taejo Wang Geon took lead directly. Constructed in the reign of King Jabi, the fortress ‘Samnyeon Sanseong’ would be used as a military base in the event of hostilities between Silla and Baekje dynasty. This fortress had a noble key role in the event of two hostile forces’s conflict. Its presence most notably revealed itself when there were confrontations between Silla and Baekje dynasty, and between the central government of Silla and the rebellious forces led by Kim Heonchang.
Over time, early in the tenth century, the fortress was situated on the south-north borders, where Wang Geon’s Goryeo in the north and Gyeon Hweon’s Hubaekje(the late Baekje dynasty) in the south confronted each other. This fortress was in control of Gyeon Hweon at that time, and there had been so many spate of violent clashes in 927 clashes between the two sides. The largest one of them all was the Battle of Gongsan Dongsu (located in current Daegu), where Wang Geon suffered a crushing defeat. Wang Geon's eagerness to redeem his defeat led him to launch a military operation against this fortress, known as the Battle of Samnyeon Sanseong.
The attack on the fortress in july of 928 by the Goryeo’s army, led by Wang Geon, was a failure. After that, he changed his strategy to focus on isolating the fortress, instead of forcibly attacking it. Due to his isolation strategy for the fortress, there had been long deadlock status until the end of war. In 936, Wang Geon finally completed the re-unification after the victory of campaign agaist the late Baekje dynasty. he named the town of Samnyeon Sanseong as Boryeong County in the year of 940. This resulted in Samnyeon Sanseong remaining not notable among the counties and prefectures of the Unified Goryeo.