Archaeological work shows Zhengzhou Shang City, an early Shang capital site in Zhengzhou, Henan, had city walls and moats.

Huanbei Shang City and some other middle Shang cities only had moats without city walls, and when it comes to the Yinxu Ruins, the late Shang capital, decadeslong archaeological excavations haven't found any city wall or moat. Maybe the need for moats and city walls lessened and their priority was reduced, says He.

He adds that city walls and moats were for defense, and came at a huge cost in terms of manpower and material resources.

When the Shang Dynasty was getting increasingly stronger, maybe it no longer needed such facilities.

However, Sun Hua points out the possibility that Yinxu had city walls or moats but the fact that we haven't found them yet does not mean they can be excluded.

"The research on Huanbei Shang City has made important progress, as part of our archaeological work on the Yinxu Ruins. It makes us see a society earlier than in Yinxu's time, a period which used to be very vague in our understanding. It fills many blanks in our study on the middle and late period of the Shang," says Wang Wei, director of the Chinese Academy of Social Sciences' Academic Division of History.