The Great Wall of China was built to protect the Chinese Empire from marauders from the north. The first sections were built in the seventh century BC. At that time, China was segmented into many small states and political municipalities of varying sizes.
Scores of troops, conscripts, and others were used to construct the Great Wall of China. The materials employed were those available proximate to the wall itself. Near Beijing, the wall is constructed from quarried limestone blocks. In other locations, it is made of quarried granite or fired brick. Where such materials are used, two finished walls are erected with packed earth and rubble fill placed in between with a final paving to form a single unit.
In some areas the blocks were cemented with a mixture of gooey rice and egg whites. In the extreme western desert locations, where good materials are in scarce supply, the wall was constructed from dirt packed between rough wood secured with woven mats.
The wall consists mainly of three types of structures; namely, beacon towers for defense and soldier accommodation, walls for fortification purposes, and passes for allowing troop and delivery-route movements in various political subdivisions.
The Great Wall is high – high enough that you would need scaling ladders. There were garrisons of soldiers posted along the wall route. They lived in little turrets built to be observation posts. Anyone mounting a ladder to scale the wall would have to face armed soldiers at the top. This defensive arrangement slowed invaders considerably but not totally.
After subjugating and uniting China from seven Warring States, the emperor began what would become the Great Wall by connecting and extending four old fortification walls along northern China circa 700 B.C. Armies were stationed along the wall as a first line of defense against the invading nomadic Hsiung Nu tribes north of China (the Huns). Signal fires from the Wall provided early warnings of an attack.