A lone plum tree blooms near the Zhumabao section of the Great Wall. [Photo by Zhao Yu for China Daily]

When talking about the history of the Great Wall, people will often think of wars and conflicts because the greatest defensive project in ancient China was used to fend off invasions by nomads from the north.

But the ancient Great Wall fortress of Zhumabao, located in today's Zhumabao village in Xinrong district the northern Shanxi city of Datong, tells another story: that of commercial and cultural exchanges between the farming Han people in the south and the nomads in the north.

With a total length of more than 20,000 kilometers, the Great Wall began construction in the Spring and Autumn Period (770-476 BC). The latest renovation and reconstruction of the project was made in the Ming Dynasty (1368-1644).

Indeed, like other sections of the Great Wall, the fortress of Zhumabao was a witness to numerous wars and conflicts before the Ming Dynasty.

Not long after the latest reconstruction, Zhumabao developed into a cross-border trade hub for the Han people in the south and the Mongolians in the north. Traded commodities included grains, tea and silk from the Han; and horses, cattle, sheep, camels and leather products from the Mongolians.

Despite short intervals of conflicts, the fortress maintained its role as a trade hub for more than 300 years. Its name, Zhumabao, translates as horse-trading fortress.

Relics related to the business is an old street called Mashi, or horse market; and the Mashilou, or horse-trading watchtower, standing on the Great Wall gate.

According to local residents, the trade was looked after by the military officers stationed in the watchtower. Every morning, the officers would come to open the gate, letting in the Mongolian traders and announcing the beginning of transactions.

Many local merchants accumulated great wealth during that period. Their fortune is demonstrated in many ancient residential buildings in the village of Zhumabao. Some well-preserved residences have now been turned into rustic lodges to accommodate tourists.

In today's Mashilou site, the gate is still there, but the watchtower is gone. And there is no more horse trading and no more building structures along the ruined street. Sometimes local herders lead their cattle through the gate, reminding people that this used to be the passageway of traded animals.

Even the Great Wall is no more intact. Its discontinuous sections are now surrounded by farmlands, grasslands and shrubs. Some scarcely scattered plum trees stand alone out of the shrubs, drawing visitors' speculation whether they were ones that offered shade to traders hundreds of years ago.

This picture of ruined beauty still appeals to tourists. The discontinuous walls and lonely trees on the grasslands offer a perfect setting for visitors to take photos.

Peng Ke'er contributed to this story.