North Korea is building a wall over the unexcavated ruins of a lost medieval city inside the demilitarized zone (DMZ), according to NK Pro analysis of satellite imagery, as part of leader Kim Jong Un’s goal to more “permanently” cut all links to South Korea.

The project to build the 3.5-mile (5.5 km) wall started in March and is nearing completion, with hundreds of soldiers living in a temporary camp on site while carrying out the work. 

It comes amid the DPRK’s large-scale efforts to carve out new defense lines in the forests of the DMZ across the inter-Korean border, after Kim ended his country’s long-standing pro-unification policy at the start of this year. 

The new wall cuts through the site of the walled capital of the Taebong kingdom (태봉국 철원성), thought to have been built in the 10th century in what is now called Cholwon County on both sides of the border (spelled Cheorwon in South Korea).

The square outline of the formerly walled 2,400-acre (970 ha) city remains visible in satellite imagery, but almost nothing else remains and little is known about it. The division of the Koreas and its location straddling the border in the DMZ has prevented proper studies.

This large flat region is unique in the DMZ as the rest of the inter-Korean border is mostly mountainous. Given its favorable geography, it’s possible a large city would exist in this location today if not for its division between the two Koreas.

The soldier camp appeared at the west end of the new wall in the first days of March, and Planet Labs satellite imagery shows work started the following month on clearing a 260-foot (80-meter) wide line across the flat but tree-covered expanse of Cholwon. 

Construction on the wall itself started in two locations along the cleared area in May. As of Nov. 11, completed wall sections measured around 1.5 miles (2.4 km) at the west end and 0.8 miles (1.3 km) on the east end, with about a mile (1.7 km) in the middle that is still being built.

The wall is sandwiched between two other wide and heavily guarded defense lines to the north and south, raising questions about its purpose and security utility or why the wall wasn’t built along one of these existing lines.

There are also multiple additional layers of trench lines running east to west to the north of the new wall, likely due to the flat and open nature of the location and related vulnerabilities in wartime. 

While North Korea has built new defense lines throughout the DMZ since this spring — in at least one case slightly crossing over the Military Demarcation Line (MDL) into the South — wall construction has not been a feature in most places.

Shorter sections of new border walls are also under construction near the new inter-Korean road and rail blockades in Kaesong on the west coast and Kosong on the east coast. Plans for a wall along the entire border appear unlikely but can’t yet be ruled out.

North Korea’s military built the road and rail blockades after setting off explosives in the two locations right up against the MDL on Oct. 15.

Experts previously told NK News that new border walls will serve as little more than “speedbumps” to South Korean forces in wartime, while assessing that they could help prevent North Koreans from escaping and serve as symbols of Kim Jong Un’s hostility toward the South.

The two Koreas agreed during the most recent period of detente in 2018 to work toward making a “joint survey and excavation of historical remains within the DMZ.” 

Efforts started on removing mines from the Taebong capital site in late 2018, but relations broke down the following year and DPRK state media brushed off the joint excavation idea as unimportant.

With the new wall construction, it is unlikely that the two Koreas will cooperate on researching the Taebong capital in the near future.

Edited by Bryan Betts