Imjonseong Fortress

Imjonseong, ringing the summit of Bongsusan in Daeheung-myeon, Yesan, became the last stronghold of the Baekje restoration movement after the kingdom fell. With a circumference of about 2.45 km it is counted as the largest of all Baekje mountain fortresses, and from its walls you look straight down over Yedang Reservoir and the Yedang plain.

The fortress that would not fall

When the Silla–Tang alliance took the Baekje capital Sabiseong in 660, the Baekje general Heukchi Sangji came to Imjonseong and raised a restoration army; the records say 30,000 men gathered within ten days. Led by Gwisil Boksin and the monk Dochim, the restoration forces fought from Imjonseong and Juryuseong, and a Silla attack on Imjonseong that August achieved little.

Even after the main restoration army was crushed at the Battle of Baekgang in 663, Imjonseong, held by Ji Su-sin, withstood Silla attacks for 30 days, thanks to the steep terrain, solid walls and plentiful food. In the end the fortress was taken by none other than Heukchi Sangji, the former restoration commander who had by then surrendered to Tang. Ji Su-sin fled to Goguryeo, and the Baekje restoration movement came to an end. That a general who once defended the fortress was the one to bring it down gives the story a bitter twist.

Later history

Imjonseong also appears in the Japanese chronicle Nihon Shoki as "Imsagisan", and it seems to have been the western regional capital when Baekje ran its territory as five regions. Under King Gyeongdeok of Unified Silla the area became Imseong county; at the end of Silla it passed to Later Baekje, until the Goryeo general Yu Geum-pil took it in 925, killing or capturing some 3,000 men including the Later Baekje commander Hyeong Jeok. In early Goryeo the area was renamed Daeheung, the name it still carries. A story says the defenders kept a huge well inside and released its water down the slope at attackers, but a Joseon-era record states there was no well or spring within the walls, so the sources disagree.

What to see

• Stone walls: a hilltop ring fortress whose outer face is built of stone and whose inner face mixes stone and earth. The southern wall is especially well preserved and gives a real sense of the fortress's scale.
• Inner ditch: a ditch 7–8 m wide runs along the inside of the walls.
• South gate site: set slightly to the east, it keeps traces of a 2.3 m wide gateway and of a square defensive enclosure in front.
• Drain: a culvert 70 cm wide and 90 cm high runs through the base of the wall, covered with stone slabs. Look for the low opening as you walk the wall.
• Thicker corners: the four corners were built about 2 m thicker than the rest of the wall for extra strength.

Tripto tips

• Getting there: from the Gwangsi-myeon side you can drive up to a car park just below the fortress, leaving only a short walk to the walls. If you hike up from the Daeheung side, you pass Daeryeonsa Temple on the way.
• Time: allow 1 hour for a section of the southern wall, or about 2 hours to follow the walls on a larger loop.
• Best time: autumn, when the air is clearest. In summer the grass around the walls grows tall, so long trousers help.
• Visiting: the fortress is a designated Historic Site, open year-round and free. There are hardly any facilities, so bring water.
• Combine with: the suspension bridge and lakeside paths of Yedang Reservoir below the mountain make it a half-day trip.