In the wide-open steppe of eastern Mongolia, archaeologists have uncovered evidence of a very long wall. This isn’t China’s Great Wall, nor does it follow a single, unbroken path. But for centuries, it silently marked the edge of a mighty empire.

This is the Medieval Wall System, or MWS — an enormous network of trenches, ramparts, and walled enclosures. The MWS once stretched across some 4,000 kilometers of what is today’s Mongolia, China, and Russia. This wall was long overlooked by archaeologists, but a new study suggests something very unusual about it: it wasn’t built for defense.

A not-so-big wall

The Great Wall of China is far from the only large-scale system of walls constructed across Eastern Asia. Several cultures built walls to protect themselves from invasions or to mark the borders of their empires. The Medieval Wall System is one of the least known ones, despite spanning such a long distance.

The MWS was built in the 10th to 12th century AD by several dynasties. The Jin dynasty (founded by people from Siberia and north-east China) contributed the most to it. In the new excavation, researchers focused on a particular enclosure that stretches across Mongolia. The “Mongolian Arc,” as this part of the wall is called, was 405 kilometers long. Researchers wanted to know what the purpose of this section was.

“We sought to determine the use of the enclosure and the Mongolian Arc”, states lead author of the research, Professor Gideon Shelach-Lavi from the Hebrew University of Jerusalem. “What was its function? Was it primarily a military system designed to defend against invading armies, or was it intended to control the empire’s outermost regions by managing border crossings, addressing civilian unrest, and preventing small-scale raids?”

Contrary to expectations, the analyzed structure running along the Mongolian Arc wasn’t a stone wall at all.

Instead, researchers found a trench, barely 70 centimeters deep, with a mound of earth beside it. In places, there was no physical barrier at all. There’s no way this would have been effective at halting armies. Instead, archaeologists suspect it may have served as a kind of visual warning, a tangible border to the empire.

Yet this didn’t seem to be just a mound to mark a border.

Plenty of artifacts, though

Inside MA03, archaeologists uncovered a small but well-fortified outpost: walls of stone and rammed earth rising a meter high, a trench for drainage, and, most notably, a semi-subterranean building with a heated stone platform — used both as stove and bed.

This feature is known as a kang in Chinese or khanzan khaalalt in Mongolian, and it’s evidence that the enclosure was likely occupied year-round. The heating system, along with ash pits, ceramics, and iron tools — including the fragment of a plow — paints a picture of a small but permanent garrison that combined pastoralism with farming and hunting. Someone lived at the outpost year-round and was relatively well-supported.

Three bronze coins from the Northern Song dynasty (960–1127) also carried a surprise. The coins were found near the furnace and ash pits, hinting at trade or tribute networks stretching across Eurasia. But coinage alone can mislead. Radiocarbon dating revealed the site was built and used during the height of the Jin dynasty, between 1150 and 1242 AD.

“Considerable investment in the garrison’s walls, as well as in the structures within them, suggests a year-round occupation”, concludes Professor Shelach-Lavi. “Future analysis of samples taken from this site will help us better understand the resources used by the people stationed at the garrison, their diet, and their way of life.”

And then, without any clear sign why, it was abandoned. Whoever lived there just left and no one came to replace them.

Then, nearly two centuries later, someone returned. Beneath a circle of stones inside the enclosure, archaeologists found a man buried in a supine position, wrapped in birchbark, with green fabric and metal objects beside him. He died around 1440 AD. His presence suggests the wall outpost, though no longer manned, remained a landmark in the cultural memory of the region.

A civilian wall?

Whenever we think of walls, we tend to think of military or at least forceful purposes. We want to keep someone out. The Great Wall of China, after all, was built to repel nomadic invasions. But the MWS, researchers now argue, wasn’t built just — or even mainly — for military purposes.

It was, first of all, a bureaucratic wall. It was a statement, built to assert sovereignty over contested terrain. The Jin dynasty likely used it to manage livestock flows, gather taxes, and regulate trade.

But this doesn’t tell the whole story. Researchers suspect that the wall was still military in some areas, and had yet another purpose: directing people to areas where it was easier to cross. The dense distribution of garrisons along the trench line suggests those stationed there would have monitored who crossed the border, and potentially stopped them if they were crossing in a dangerous or not permitted place.

This shows that medieval powers in Asia placed great value not just on military infrastructure, but also on civilian concerns. They were willing to invest a lot of resources to publicly display their power and facilitate trade across the steppe.

Future excavations will hopefully shed even more light on these walls and the civilizations that built them. For now, the MWS seems to tell a complex story: one not just of war and exclusion, but also of trade and administration.