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