The Structure of the Great Wall

• Passes(the Fortresses of the Passes)
China had the Great Wall, but China was not completely cut off from the rest of the world. It traded with many other countries so there had to be gates in and out of China along the Wall. These gates were typically located at a pass, but a plain gate would be too weak, so complex constructions were necessary. Sometimes there was simply a double gate to form a pass. In other cases they built a virtual fortress with a labyrinth to confuse anyone who tried to invade. It was very important to make the design so that a

Passes / Fortresses of great wall

small number of defenders could repel a much larger attacking force. Now the pass not only means the fortress but also the whole area the fortress located.

•  Gates
The gate had enormous double timber doors with huge iron bolts and locking rings. Above each gate was a tower, 2-3 stories high so soldiers could watch for anyone who could cause trouble. The towers were wooden or brick, or sometimes both.

 
gates of great wall
• Wengcheng:
In fact, it's a kind of TRAP. There was a double gate which served as the main entrance to the fortress. If the enemy broke through the first one, they ended up being trapped between the outer gate and the inner gate. So the Chinese defenders could kill them before they had a chance to climb over the wall.
 

Wengcheng of great wall
 

•  Beacon Towers
Beacon Towers , usually built at regular intervals on both sides of the wall. Most of them are independent structures, occupying a commanding position, like hill peaks or bends of river/road. It is said wolves' dung was used to make a column of smoke during the day, while firewood for making a bonfire during the night. Plus, the shot of a cannon could transmit messages as well - one shot stands for a certain amount of the enemy. So whenever the enemy was spotted, the specific news of enemy movements was swiftly sent back to the nearby barracks or fortresses, until finally to the capital.
 

 

Beacon tower of great wall

•  Platforms and Watchtowers
Numerous platforms and watchtowers were built into the Great Wall. The platform was fairly simple with four walls topped with battlements for use by archers. The heavily-built watchtowers are usually two-story structures, made of stone slabs and bricks, plus a wooden shelter on the
top. The upper floor is supported by a number of arches, and the spaces inside were used to accommodate soldiers and store arms in times of war. Depending upon the size of the platform, the access to second floor was via inside stairs or merely a rope ladder. From a lookout at the top, guards could get an excellent view and archers could easily fire on any invaders. Signaling devices could be torches, bells, drums and gongs. There were some 1200 platforms and watchtowers along the stretch of wall between Beijing and the Shanhaiguan Fortress. The 158 fortified towers located near Gubeikou are particularly remarkable.
 
Watchtower of great wall

•  Battlements
These crenellated battlements on the outer side of the Wall provided cover for archers who could fire at the enemy through special slits. These slits were narrow on the inside but wide on the outside so the archers had a wide angle of vision while enjoying maximum protection. These slits were lower for the archers and higher for the lookouts.

•  Parapet/Nuqiang
This is the low parapet on inner side of the wall, usually one meter high. It was built to prevent both men and horses from falling off the wall.

•  Obstacle Wall / Walls-within-walls
This is a series of small walls built vertically to the main wall as part of the defense system. Soldiers could fight behind these small walls against the enemies who had already climbed up the main wall.

•  The Single Parapet Wall
This means a solid narrow wall without battlements and Nuqiang. Much of the Wall is wide enough for people and horses to walk on top of it, but you could not travel on top of this kind of wall. The terrain in these places was so rugged, that it was not necessary or impossible to build a wide wall, two-three-metre high and less than one metre wide.

Battlement and parapet of great wall
Obstacle wall of great wall
Single parapet wall of great wall

•  Drainage system
Drainage channels and waterspout were built at regular intervals, so that the rain would drain away, The waterspout usually extended 1 meter beyond the wall, and a stone receptacle below made sure that water was directed away from the foundations of the wall.

•  Horse-ramp/ Ma dao
Ramps and ladders within the pass provided access for both horses and men to the top of the wall. The ramp was five to six meters wide and approximately 30 degrees. Foothold raised courses of bricks were set across the ramp so that horses can easily travel on it.

•  Brick-with-words
A special brick engraved with the date of manufacture and its maker.

•  Cihou
Cihou is a solid command post with no roof, giving the defenders a 360-degree-view of the whole area. This 4-sided structure has 24 observation holes(6 on each side).

Drainage system of great wall
Madao of great wall
Cihou of great wall