A 13000 mile dragon of earth and stone

winds its way through the countryside of China

with a history almost as long and serpentine蜿蜒的，弯弯曲曲的 as the structure

The great wall began as multiple walls of rammed earth素土夯实

built by individual feudal states during the Chunqiu period

to protect against nomadic游牧的; 流浪的 raiders north of China and each other

when emperor Qin Shi Huang unified the states in 221 BCE

The Tibetan Plateau and Pacific Ocean became natural barriers

but the mountains in the north remained vulnerable to Mongol, Turkish and Xiongnu invasions

To defend against them

the emperor expanded the small walls built by his predecessors祖先

connecting some and fortifying增强；筑防御工事于 others

As the structure grew from Lintao临洮in the west

to Liaodong辽东 in the east

they collectively became known as the Long Wall

To accomplish this task

The emperor enlisted征募soldiers and commoners平民

not always voluntarily

Of the hundreds of thousands of builders recorded during the Qin Dynasty

many were forcibly conscripted应征入伍的 peasants

and others were criminal serving out sentences

Under the Han Dynasty

the wall grew longer still

reaching 3700 miles

and spanning from Dunhuang to the Bohai sea

Forced labor continued under the Han Emperor Han-Wudi

and the walls reputation grew into a notorious臭名昭著的place of suffering

poems and legends of the time told of labors buried in the nearby mass graves乱葬岗

or even within the wall itself

And while no human remains have been found inside

grave pits do indicate that many workers died from accidents, hunger and exhaustion

The wall was formidable难以对付的 but not invincible不可战胜的

Both Genghis成吉思汗 and his son Khublai Khan忽必烈 managed to surmount the wall

during the Mongol invasion of the 13^th Century

After the Ming Dynasty gained control in 1368

they began to refortify and further consolidate the wall

using bricks and stones from local kilns窑炉

Averaging 23 feet high and 21 feet wide

the walls 5500 miles were punctuated by watchtowers瞭望塔

When raiders入侵者 were sighted

fire and smoke signals traveled between towers

until reinforcements arrived

small openings along the wall let archers弓箭手 fire on invaders

while larger ones were used to drop stones and more

but even this new and improved wall was not enough

In 1644, northern Manchu clans氏族，宗族 overthrew the Ming

to establish the Qing Dynasty

incorporating Mongolia as well

Thus, for the second time

China was ruled by the very people

the wall had tried to keep out

With the empire’s borders now extending beyond the Great Wall

the fortifications lost their purpose

and without regular reinforcement

the wall fell into disrepair

rammed earth eroded

while brick and stone were plundered抢劫，掠夺 for building materials

but its job wasn’t finished

During World WarⅡ

China used sections for defense against Japanese invasion

and some parts are still rumored to be used for military training

but the wall’s main purpose today is cultural

As one of the largest man-made structures on earth

It was granted UNESCO World Heritage Status in 1987

Originally built to keep people out of China

The Great Wall now welcomes millions of visitors each year

In fact, the influx流入of tourists has caused the wall to deteriorate变坏

leading the Chinese government to launch preservation initiatives

It’s also often acclaimed as the only man-made structure visible from space

Unfortunately, that’s not at all true

In low earth orbit轨道, all sorts of structures

like bridges, highways and airports are visible

and the Great Wall is only barely discernible可辨识的

From the moon, it doesn’t stand a chance有希望，有可能

But regardless, it’s the earth we should be studying it from

because new sections are still discovered every few years

branching off from the main body

and expanding this remarkable monument to human achievement