The architect of this defence system was Weng Wan Da. At the time there were two defence lines: the outer frontier and the secondary frontier. Datong and Xuanfu lay between them. Theoretically, enemies would have to fight through both in attacking the Ming. Realistically, the secondary frontier was the Ming's main defence.
Weng proposed building walls in the north to protect against the most common avenues of attack. He intended making the outer frontier a real barrier to attackers. By 1547, Weng's proposals - and the 333 miles of wall that went with it - were almost complete.
Weng divided each frontier into three sections. The outer frontier's first section, which ran for 85 miles, went northwest from the Yellow River at Baodezhou to Laoying. The second began at Yajiaoshan and ran 216 miles to Yanghe. The final stretch ran 341 miles from Yanghe to Yongning and Sihaiye, north of Beijing.
The secondary frontier was not as continuous. It began at Laoying and turned south and east for 267 miles. The second section ran for about 357 miles from Baoding, southwest of Beijing and running northwest to Yanhegou. The last section began at Beijing and ran for 60 miles. Hundreds of forts and signal towers were part of the construction.
Weng thus laid the foundation for a defence system which remained and was used as a basis for further construction. At its peak, there were 528 miles of wall arranged in three sections: the river wall, the outer border and the inner border.
