-- secrets continued--

• The Ming Dynasty built much of what remains today. They were driven by desperation to build the ultimate defense and lock the northern frontier once and for all. The Ming renovated the old Qin and Han walls and extended them. The Ming wall stretched some 4,500 miles from the Korean border at Dandong to the city of Jayuguan in the western desert.

• The Ming bricks were a marvel of engineering holding up to a pressure of over 1000 pounds per square inch. The mortar was of super strength. The mortar was stronger than the bricks themselves. The puzzle of this super strength has now been solved. The mystery ingredient was rice flour. With innovations like these, the Ming was able to build spectacular monuments. A feature of the wall was water drainage systems that channeled the water to the Chinese side and withheld the water to the enemy side and thus inhibits plant growth and so deny cover to the attackers.

• Warning towers were built in enemy territory. The armies were controlled from watchtowers that were built every 200 yards along the Ming walls. Later cannon were used. Having discovered gunpowder, the Ming was also the first to use hand grenades and mines. Stones were also pushed through special openings to create manmade avalanches to crush the enemy. If the attackers succeeded in scaling the wall, the defenders could retreat to the guard towers. These guard towers were only accessible by retractable ladders.