In 1568, Tan Lun was appointed senior vice minister of war and supreme commander of the defence areas of Chi and Liao - both of which had weak fortifications. The following year, he submitted a plan which would divide the 800-mile border between Shanhaiguan and Zhenbiancheng into 12 sections. Three thousand signal towers would be built - 1,000 a year - each of which would hold 50 soldiers. They would be 30 feet high and 120 feet in circumference. The cost would be 65,000 ounces of silver.
Other ambitious plans were put forward and repairs proposed, many of which were still being carried out when the [G 11 / Manchus], a non-Chinese tribe, rode into Beijing in 1644 and overthrew the Ming.
