The Great
Wall of China is a series of
stone and earthen fortifications in northern China,
built originally to protect the northern borders of the Chinese
Empire against intrusions by various nomadic
groups. Several walls have been built since the 5th century BC that are
referred to collectively as the Great Wall, which has been rebuilt and
maintained from the 5th century BC through the 16th century. One of the most
famous is the wall built between 220–206 BC by the first Emperor
of China, Qin
Shi Huang.
Little of that wall remains; the majority of the existing wall was built during
the Ming
Dynasty.
The Great Wall stretches from Shanhaiguan in the east, to Lop
Lake in the west, along an arc that roughly
delineates the southern edge of Inner
Mongolia.
The most comprehensive archaeological survey, using advanced technologies, has
concluded that all the walls measure 8,851.8 km (5,500.3 mi).This is made up of
6,259.6 km (3,889.5 mi) sections of actual wall, 359.7 km
(223.5 mi) of trenches and 2,232.5 km (1,387.2 mi) of natural
defensive barriers such as hills and rivers.
History
The
early walls
The
Chinese were already familiar with the techniques of wall-building by
the time of the Spring and Autumn
Period, which began around the 8th century
BC. During the Warring States
Period from the 5th century BCE to 221 BCE, the states of Qin, Wei, Zhao, Qi, Yan and Zhongshan all constructed extensive
fortifications to defend their own borders. 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.
Qin Shi Huang conquered all opposing states and
unified China in 221 BCE, establishing the Qin Dynasty.
Intending to impose centralized rule and prevent the resurgence of feudal
lords, he ordered the destruction of the wall sections that divided his empire
along the former state borders. To protect the empire against intrusions by the Xiongnu people from the north, he ordered
the building of a new wall to connect the remaining fortifications along the
empire's new northern frontier. Transporting the large quantity of materials
required for construction was difficult, so builders always tried to use local
resources. Stones from the mountains were used over mountain ranges, while rammed earth was used for construction in the
plains. There are no surviving historical records indicating the exact length
and course of the Qin Dynasty walls. Most of the ancient walls have eroded away
over the centuries, and very few sections remain today. The human cost of the
construction is unknown, but it has been estimated by some authors that
hundreds of thousands, if not up to a million, workers died
building the Qin wall. Later, the Han, Sui,
and Northern 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. The Liao carried out limited
repair of the Great Wall in a few areas, however the Jin did construct
defensive walls in the 12th century, but those were located much to the north
of the Great Wall as we know it, within today's Inner and Outer Mongolia.
Characteristics
Before
the use of bricks, the Great Wall was mainly built from rammed earth,
stones, and wood. During the Ming Dynasty, however, bricks were heavily used in
many areas of the wall, as were materials such as tiles, lime,
and stone. The size and weight of the bricks made them easier to work with than
earth and stone, so construction quickened. Additionally, bricks could bear
more weight and endure better than rammed earth. Stone can hold under its own
weight better than brick, but is more difficult to use. Consequently, stones
cut in rectangular shapes were used for the foundation, inner and outer brims, and gateways of
the wall. Battlements line the uppermost portion of the
vast majority of the wall, with defensive gaps a little over 30 cm
(12 in) tall, and about 23 cm (9.1 in) wide.
Condition
While
some portions north of Beijing and near tourist centers have been preserved and
even extensively renovated, in many locations the Wall is in disrepair. Those
parts might serve as a village playground or a source of stones to rebuild houses
and roads. Sections of the Wall are also prone
to graffiti and vandalism.
Parts have been destroyed because the Wall is in the way of construction.
More
than 60 km (37 mi) of the wall in Gansu province
may disappear in the next 20 years, due to erosion from sandstorms.
In places, the height of the wall has been reduced from more than five meters
(16.4 ft) to less than two meters. The square lookout towers that
characterize the most famous images of the wall have disappeared completely.
Many western sections of the wall are constructed from mud, rather than brick and stone, and thus are more susceptible
to erosion.
Visibility from the moon
One of the earliest known references to this myth
appears in a letter written in 1754 by the English antiquary William
Stukeley.
Stukeley wrote that, "This mighty wall of four score miles in length (Hadrian's
Wall)
is only exceeded by the Chinese Wall, which makes a considerable figure upon
the terrestrial
globe,
and may be discerned at the moon." The claim was also
mentioned by Henry
Norman in 1895 where he states "besides
its age it enjoys the reputation of being the only work of human hands on the
globe visible from the moon." The issue of
"canals" on Mars was prominent in the late 19th century and may have
led to the belief that long, thin objects were visible from space. The claim that the
Great Wall is visible also appears in 1932's Ripley's Believe it or Not strip and in Richard Halliburton's 1938 book Second Book of Marvels.
The claim the Great Wall is visible has been debunked
many times, but is still
ingrained in popular culture. The wall is a maximum
9.1 m (30 ft) wide, and is about the same color as the soil
surrounding it. Based on the optics of resolving power (distance versus the
width of the iris: a few millimeters for the human eye, meters for large
telescopes) only an object of reasonable contrast to its surroundings which is
70 mi (110 km) or more in diameter (1 arc-minute) would be visible to
the unaided eye from the moon, whose average distance from Earth is 384,393 km
(238,851 mi). The apparent width of the Great Wall from the moon is the same as
that of a human hair viewed from 2 miles (3.2 km) away. To see the wall
from the moon would require spatial resolution 17,000 times better than normal
(20/20) vision. Unsurprisingly, no
lunar astronaut has ever claimed to have seen the Great Wall from the moon.
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