Hanseong on the south bank, and a line of watch-posts

A Korean historical essay follows the Hangang basin from the late fourth century to the mid-sixth, as three states took it in turn and put it to different uses. In the late fourth century Hanseong Baekje made the basin the political, military, and economic centre of the kingdom, and the base from which the state was run. Hanseong itself is identified with Pungnaptoseong or Mongchontoseong: on the south bank of the Hangang, on the riverside. The reason given for placing the capital there is that the spot was already a centre of water and land routes — an inland corridor toward the West Sea, and a place from which overseas trade and the movement of goods could be managed. In the time of King Gaero the kingdom is described as controlling traffic along the main waterways and as adjusting its ties with neighbouring powers. That is treated as more than a defence of the capital’s outskirts: a strategic base for the running of the state as a whole.

The purpose of the defence, in this reading, was to protect the capital, and the greatest danger in view was Goguryeo’s southward advance. Hanseong, on the south bank, could use the river as a last line; a first line was still needed further out, to see an approach in time. Watch-posts in the Achasan and Yongmasan area are described as having been laid out so that they could see one another, and so that a force could move quickly in an emergency. King Gaero is described as using the ground around Hanseong, and the mountain fortresses and posts, to that end. The same line of posts is also treated as a way of holding roads and waterways, and of adjusting relations with local powers — a military work that also served economic and political control. Yeo Ho-gyu’s 2013 essay, in Baekje Culture, on the changing Goguryeo–Baekje border from the late fifth century to the mid-sixth, is among the modern studies relied on here. Those readings are left with that scholarship.

475, and a basin remade as a southern base

In the mid-fifth century, after the capital had been moved to Pyongyang, King Jangsu pressed a southward policy in earnest. Northern powers had already begun to appear, and the move of the capital is treated as the moment when that southward policy took a concrete form, and when pressure on Baekje and Silla tightened. In the Goguryeo annals of the Samguk sagi, in the chapter on King Jangsu, 475 is the year he killed King Gaero of Baekje and took Hanseong. The capture is read as a result of that policy, as a turning point in the southern strategy, and as a shift in the balance among the three states.

After the occupation, Goguryeo is described as reorganising the basin as a military and administrative base, and as a hinge of the southward policy. The reason given is that the Hangang had already been a hub of water and land traffic under Baekje; to hold it was to hold that network. Park Jong-seo, in 2016, in Goguryeo Balhae Research, is cited for a traffic network made along the Hangang in the course of King Jangsu’s advance, turning the area into a strategic point. Yeo Ho-gyu is also cited, in a 2017 piece, on the changing border in the same centuries.

Watch-posts in the Achasan area are given an auxiliary part in the occupation. According to the literature cited, including Lee Jeong-beom in 2015, also in Goguryeo Balhae Research, they served watch and liaison, and helped keep order and control goods in the occupied zone. The posts are treated as a device in support of the larger policy, not as the heart of the event itself. Those claims are left with the chronicle date and the modern studies.

An alliance, a break in 553, and Sinju on the river

Early in the sixth century Silla and Baekje, through a Silla–Baekje alliance, checked Goguryeo’s southward policy. The alliance is treated as a way of keeping a balance among the three states, and Silla, in the occupied zones, as limiting Goguryeo’s reach by holding traffic and the movement of goods. In the Silla and Baekje annals of the Samguk sagi, as cited here, Silla secured the upper Hangang in 551, and in 553 broke with Baekje and took the lower river as well.

That is read not as a simple military occupation but as a move to secure the basin’s traffic and economic resources and to set a base for state control. Silla established Sinju in the occupied area, to strengthen administration and to hold the roads and the river transport, and to bring the basin into Silla’s own system rather than leave it a mere military post. Kim Deok-won’s two 2021 essays — one in Military History, on the process of Silla’s advance in King Jinheung’s reign, and one in Seoul and History, on its background — are cited here. Silla is also described as using some of the older Goguryeo defences, and as joining regional government to military strategy, until it held the basin as a whole and a stronger place in the triangular balance.

From the late fourth century to the mid-sixth, then, the basin is read as a space in which three states competed in order to keep and to extend a state system, not only as a battlefield. Hanseong Baekje had run the capital from it; Goguryeo, after 475, remade it as a southern hinge; Silla, after the mid-sixth-century alliance and the break that followed, administered it through Sinju. How each state took the basin, and what it then did with it, is treated as a way of seeing the balance among the three. Those dates and readings are left with the chronicles as cited and with the studies from 2013 to 2021. The same Korean report, at fuller length, is on CampusDown.

Sources

1. Samguk sagi, Goguryeo annals, chapter on King Jangsu (475); Silla and Baekje annals, as cited for 551 and 553.
2. Yeo Ho-gyu, “Changes in the Goguryeo–Baekje border from the late fifth century to the mid-sixth,” Baekje Culture, 2013; and a 2017 essay in Ancient History Research.
3. Park Jong-seo, “Goguryeo’s advance into the Hangang basin under King Jangsu and the running of the southern route,” Goguryeo Balhae Research, 2016.
4. Lee Jeong-beom, “Goguryeo’s form of rule in the Hangang basin in the fifth and sixth centuries,” Goguryeo Balhae Research, 2015.
5. Kim Deok-won, “The process of Silla’s advance into the Hangang basin in King Jinheung’s reign,” Military History, Institute for Military History, 2021; and “The background of Silla’s advance into the Hangang basin in King Jinheung’s reign,” Seoul and History, Seoul Historiography Institute, 2021.

Last updated: 14 November 2026