From the ancient times, Shanxi was called the strategic gateway of the national capital. An impregnable defensive system is required to guard Shanxi, therefore, the defense settlement rose in response to the request, shaped as a city surrounded by many successive forts. Beyond the government building forts, there were a lot of civilian communities. According to the form and the size, the defense system could be distinguished as the following: Town City—Road City—Wei City－Suo City－Fort City —Community Fort. It was constructed as this: guarding system (outside) --- transportation system--- building units. The three layers affected and restricted each other.