The Northern Line

The Northern Line extends for 737 kilometers across parts of present-day northeastern China, southern Siberia, and Mongolia. In Mongolia, it traverses sparsely populated and largely undisturbed steppe. Unlike other defensive systems, this line is not connected to adjacent wall networks. Instead, it runs between two mountain ranges—the Da Xingan Range in the east and the Khentii Mountains in the west—effectively sealing off the wide lowland corridor between them. Our remote-sensing and ground surveys identified 72 individual structures along the course of the line, grouped into 42 clusters, each containing between one and three structures. In 2018, we conducted vehicle-based and pedestrian surveys along the Mongolian segments of the line. Subsequent campaigns in 2019, 2021, 2022, and 2024 included targeted surveys, geophysical investigations, and excavations at three of these clusters. Radiocarbon (C¹⁴) samples from the sites date the construction and use of the Northern Line to the period between the 11th and early 12th centuries CE, suggesting that it was built under the Khitan (Liao) dynasty (916–1125). One particularly striking discovery is that, while the structures (enclosures or camps) are surrounded by massive rammed-earth walls and deep ditches, the “wall” line itself consists only of a ditch—approximately 2 meters deep and 4 meters wide—with no corresponding wall built on its inner (southern) side.