This is when most of the [M 002 / Ming walls] were built, although the policy was first initiated in the 15th century. Extensive wall building was undertaken in Xuanfu and Datong, west of the capital. By the end of the century, the walls that we see today had been completed.
The key defence points were at Liaodong in Manchuria; Jizhou northeast of Beijing; Xuanfu northwest of Beijing; Datong in northern Shaanxi; Shaanxi or Taiyuan to the west; Yansui or Yulin south of the [G 15 / Ordos]; Guyuan near central [M 004 / Shanxi; Ningxia and Gansu]. Various accounts of their locations exist and there is also some doubt as to their number.
