The Great Wall of China is a catch-all term for a series of stone and earthen fortifications running across northern China, built mostly between the 5th century BC and the 16th century. The primary aim was to defend the northern borders of the Chinese empire. By the Warring States period (453-221 BC) various kingdoms around China had built walls to protect themselves. When Emperor Qin Shihuangdi unified the warring states of the central plains in 221 B.C. he began working on a centralized rule to prevent the resurgence of feudal power. In doing so he removed sections of wall which divided his empire and turned his attention primarily on fortifications to protect land he had taken from the northern neighbours. Most of these took the form of compacted earth or gravel.
The walls were typically built in vulnerable territory to deter raiding parties and many highland sections were simply watch towers on crags. Since it was never one entity, no one really knows its true length. Small quantities of locally fired brick didn’t appear in wall building until the first half of the sixteenth century. The size and weight of the bricks made them much easier to work with and construction quickened. Stones continued to be laid as foundations, outer brims and gateways.
An estimated 2 to 3 million men died working on the project throughout history, though none were buried in its foundations as is sometimes reported. The Ming wall was built by soldiers and civilian laborers. Texts have suggested that at its peak the Ming wall was guarded by close to a million men helping defend the empire against the Mongols and later Manchus. Smoke signals and gunpowder blasts enabled soldiers to pinpoint the locations under attack and notify reinforcements. Stones were also packed with gunpowder to make grenades whist the Mongols used bows and arrows. Sometimes the wall was very effective and sometimes not. In 1554 thousands of Mongols were successfully held off outside today’s Jinshanling, and Badaling sections. However the Yuan and Qing dynasties are examples of where the Chinese defenses failed and the country was taken over by foreigners.
Much of the Great Wall now lies in a state of disrepair, and at least 60 kilometers of the older, compacted earth wall may disappear in Gansu province over the next 20 years due to sandstorms alone. If you could see the Great Wall with the naked eye from the moon you would also be able to view a human hair from two miles away!