https://www.worldatlas.com/articles/walled-cities-of-the-world.html
Walled Cities of the World
These historic cities are unique for their existing city walls, many of which were constructed many centuries ago.
walled citiesof theworld
https://www.econstor.eu/handle/10419/193245
EconStor: Walled Cities and Urban Density in China
EconStor is a publication server for scholarly economic literature, provided as a non-commercial public service by the ZBW.
cities and urbaneconstorwalleddensitychina