Do observe the Wall's many signal towers...which reflect how communication between the army units along the length of the Great Wall (including the ability to call reinforcements and warn garrisons of enemy movements) was of high importance. Signal towers were built upon hill tops or other high points along the wall for their visibility...and were placed no further that "two arrow shots" apart to sustain full control. This is no mere barricade...there is much to ponder when in situ...and the whole story is very complex indeed.
Do you want to know a bit more?...in a nutshell...
The Great Wall of China is a series of fortifications running in general east to west through the entire northern part of China. Experts have concluded that all the walls measure just short of 9,000 kilometres. Most of the ancient walls have eroded away over the centuries, and very few original sections remain today.
The Wall was built originally to protect the northern borders of the Chinese Empire against intrusions by various nomadic groups or military incursions. The defensive characteristics of the Great Wall were enhanced by the construction of watch towers, troop barracks, garrison stations, signaling capabilities through the means smoke or fire.
Several walls had already been begun to be built beginning around the 7th century BC...and these, later joined together and made bigger, stronger, and unified are now collectively referred to as the Great Wall. Especially famous is the wall built between 220-206 BC by the first Emperor China, Qin Shi Huang. Little of that wall remains. Since then, the Great Wall has on and off been rebuilt, maintained, enhanced; the majority of the existing wall was reconstructed during the Ming Dynasty. Built to withstand the attack of small arms such as swords and spears, these walls were made mostly by stamping earth and gravel between board frames.
THE FIRST EMPEROR'S NEW WALL
China's First Emperor, Qin Shi Huang, conquered all opposing states and unified China in 221 BC, establishing the Qin Dynasty. Imposing centralized rule and preventing the resurgence of feudal lords, he ordered the destruction of the wall sections that divided his empire along the former state borders. To protect against intrusions from the north, he ordered the building of a new wall to connect the remaining fortifications along the empire's new northern frontier.
The First Emperor is also the same man who ordered the construction of an underground 'spirit army' to protect him for eternity at Xi'an. The Army of Terracotta Warriors is now as popular with visitors as the Great Wall itself.
Later dynasties all repaired, rebuilt, or expanded sections of the Great Wall at great cost to defend themselves against northern invaders. The Tang and Song dynasties did not build any walls in the region. The Liao, Jin and Yuan dynasties, who ruled Northern China throughout most of the 10-13th centuries, had their original power bases north of the Great Wall proper; accordingly, they would have no need throughout most of their history to build a wall along this line.
REVIVED DURING THE MING DYNASTY
Towards the end of the Ming Dynasty, the Great Wall helped defend the empire against the Manchu invasions that began around 1600. The Manchus were finally able to cross the Great Wall in 1644, and quickly seized Beijing, and defeated both the rebel-founded Shun Dynasty, and the remaining Ming resistance, establishing the Qing Dynasty rule over all of China.