Ni hao! In this blog I start out with a photo of me at Badaling. Badaling 八达岭 is the site of the most visited section of the Great Wall of China, approximately 50 miles northwest of Beijing city within the Beijing Municipality. The portion of the wall running through the site was built during the Ming Dynasty, along with a military outpost reflecting the location's strategic importance. The portion of the wall at
Badaling has undergone heavy restoration, and in 1957 it was the first section of the wall to open to tourists. Now visited annually by millions, the immediate area has seen significant development, including hotels, restaurants, and a cable car. The recently completed Badaling Expressway connects Badaling with Beijing city. It was here that President Richard Nixon and his wife, accompanied by Vice Premier Li Xiannian, visited on February 24, 1972, during his historic journey to China. The Great Wall of China 长城) is a series of stone and earthen fortifications in China, built, rebuilt, and maintained between the 5th century BC and the 16th century to protect the northern borders of the Chinese Empire during the rule of Successive dynasties. Several walls, referred to as the Great 
Wall of China, were built since the 5th century BC, the most famous being the one built between 220 BC and 200 BC by the first Emperor of China, Qin Shi Huang. That wall was much farther north than the current wall, built during the Ming Dynasty, and little of it remains. The Great Wall is the world's longest human-made structure, stretching over approximately 6.400 km (4,000 miles) from Shanhai Pass in the east to Lop Nur in the west, along an arc that roughly delineates the southern edge of Inner Mongolia. It is also the largest human-made structure ever built in terms of surface area and mass. History: 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 cetury BC to 221 BC, the states of Qi, Yan and Zhao 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 BC, 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 (Turks) 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. Later, the Han, Sui, Northern and Jin dynasties all repaired, rebuilt, or expanded sections of the Great Wall at great cost to defend themselves against northern invaders. The Great Wall concept was revived again during the Ming Dynasty following the Ming army's defeat by the Mongols in the Battle of Tumu in 1449. The Ming had failed to gain a clear upper-hand over the Mongols after successive battles, and the long-drawn conflict was taking a toll on the empire. 
The Ming adopted a new strategy to keep the Mongols out by constructing walls along the northern border of China. Acknowledging the Mongol control established in the Ordos Desert, the wall followed the desert's southern edge instead of incorporating the bend of the Huang He. Unlike the earlier Qin fortifications, the Ming construction was stronger and more elaborate due to the use of bricks and stone instead of rammed earth. As Mongol raids continued periodically over the years, the Ming devoted considerable resources to repair and reinforce the walls. Sections near the Ming capital of Beijing were especially strengthened. Towards the end of the Ming Dynasty, the Great Wall helped defend the empire against the Manchu invasions that began around 1600. 
Under the military command of Yuan Chonghuan, the Ming army held off the Manchus at the heavily fortified Shanhai Pass, preventing the Manchus from entering the Liaodong Peninsula and the Chinese heartland. The Manchus were finally able to cross the Great Wall in 1644, when the gates of Shanhai Pass were opened by Wu Sangui, a corrupt Ming border general, after being bribed. The Manchus quickly seized Beijing, and defeated the newly founded Shun Dynasty and remaining Ming resistance, to establish the Qing Dynasty. Under Qing rule, China's borders extended beyond the walls and Mongolia was annexed into the empire, so construction and repairs on the Great Wall were discontinued. Notable areas: The following three sections are in Beijing municipality, which were renovated and which are regularly 
visited by modern tourists: The "North Pass" of Juyongguan pass, known as the Badaling. When used by the Chinese to protect their land, this section of the wall has had many guards to defend China’s capital, Beijing. Made of stone and bricks from the hills, this portion of the Great Wall is 7.8 meters (25.6 ft) high and 5 meters (16.4 ft) wide. One of the most striking sections of the Ming Great Wall is where it climbs extremely steep slopes. It runs 11 kilometers (7 mi) long, ranges from 5 to 8 meters (16–26 ft) in height, and 6 meters (19.7 ft) across the bottom, narrowing up to 5 meters (16.4 ft) across the top. Wangjinglou is one of Jinshanling's 67 watchtowers, 980 meters (3,215 ft)above sea level. South East of Jinshanling, is the Mutianyu Great Wall which winds along lofty, 
cragged mountains from the southeast to the northwest for approximately 2.25 kilometers (about 1.3 miles). It is connected with Juyongguan Pass to the west and Gubeikou to the east. Another notable section lies near the eastern extremity of the wall, where the first pass of the Great Wall was built on the Shanhaiguan (known as the “Number One Pass Under Heaven”), the first mountain the Great Wall climbs. Jia Shan is also here, as is the Jiumenkou, which is the only portion of the wall that was built as a bridge. Shanhaiguan Great Wall is called the “Museum of the Construction of the Great Wall”, because of the Meng Jiang-Nu Temple, built during the Song Dynasty. Characteristics: Before the use of bricks, the Great Wall was mainly built from 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 (a foot) tall, and about 23 cm (9 inches) wide. The steps that form the Great Wall of China are very steep and tall in some areas. Tourists often become exhausted climbing the wall and walk no more than a kilometre or two (around a mile). Condition: While some portions north of 
Beijing and near tourist centers have been preserved and even reconstructed, 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. No comprehensive survey of the wall has been carried out, so it is not possible to say how much of it survives, especially in remote areas. Intact or repaired portions of the Wall near developed tourist areas are often frequented by sellers of tourist kitsch. A remote western section of the Great Wall, Jiayuguan Pass, Gansu. This section of the wall is seriously threatened by environmental damage and erosion. More than 60 kilometers 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 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. Watchtowers and barracks: The wall also has watch towers at regular intervals, which were used to house women and troops, and send smoke signals. Barracks and administrative centers are located at larger intervals. 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 invisibility. 
Recognition: The Wall was made a UNESCO World Heritage Site in 1987. Mao Zedong had a saying, "You're not a real man if you haven't climbed the Great Wall" 不到长城非好汉. Originally this saying was used to bolster his revolution in trekking north. But over time the saying has been reduced to a promotional swag for the Great Wall of China. In Badaling (north of Beijing) the 'real carrot stone' can be found with the saying engraved on it. Lists of recommended travel destinations often feature the Great Wall of China, which also appears in several listings of even wonders of the modern world -- including the recently announced New Seven Wonders of the World which claimed to record a 100 million votes. Visibility: The Great Wall of China is seen in a false-color radar image from the Space Shuttle, taken in April 1994. Ripley´s Believe It or Not! cartoon from May 1932 explains the fact that the wall is "the mightiest work of man, 
the only one that would be visible to the human eye from the moon" and Richard Halliburton's 1938 book Second Book of Marvels makes a similar claim. This belief has persisted, assuming urban legend status, sometimes even entering school textbooks. Arthur Waldron, author of history of the Great Wall, has speculated that the belief might go back to the fascination with the "canals" once believed to exist on Mars. (The logic was simple: If people on Earth can see the Martians' canals, the Martians might be able to see the Great Wall.) The Great Wall is a maximum 30 ft (9.1m) 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 millimetres for the human eye, metres for large telescopes) an object of reasonable contrast to its surroundings some four thousand miles in diameter (such as the Australian land mass) would be visible to the unaided eye 
from the moon (average distance from earth 238,857 miles (384,393 km)). But the Great Wall is of course not a disc but more like a thread, and a thread a foot (30cm) long would not be visible from a hundred yards (90 m) away, even though a human head is. Not surprisingly, no lunar astronaut has ever claimed he could see the Great Wall from the moon. A different question is whether it is visible from near-Earth orbit, i.e at an altitude of less than 500 kilometers (311 mi) (0.1% of the distance of the moon). The consensus here is that it is barely visible, and only under nearly perfect conditions; it is no more conspicuous than many other manmade objects. Astronaut William Pogue thought he had seen it from Skylab but discovered he was actually looking at the Grand 
Canal of China near Beijing. He spotted the Great Wall with binoculars, but said that "it wasn't visible to the unaided eye." US Senator Jake Garn claimed to be able to see the Great Wall with the naked eye from a space shuttle orbit in the early 1980s, but his claim has been disputed by several US astronauts. Chinese astronaut Yang Liwei said he could not see it at all. Veteran US astronaut Gene Cernan has stated: "At Earth orbit of 160 kilometers (99 mi) to 320 kilometers (199 mi) high, the Great Wall of China is, indeed, visible to the naked eye." Ed Lu, Expedition 7 Science Officer aboard the International Space Station, adds that, "it's less visible than a lot of other objects. And you have to know where to look." Neil Armstrong stated about the view from Apollo 11: "I do not believe that, at least with my eyes, there would be any man-made object that I could see. 
I have not yet found somebody who has told me they've seen the Wall of China from Earth orbit. ... I've asked various people, particularly Shuttle guys, that have been many orbits around China in the daytime, and the ones I've talked to didn't see it." Leroy Chiao, a Chinese-American astronaut, took a photograph from the International Space Station that shows the wall. It was so indistinct that the photographer was not certain he had actually captured it. Based on the photograph, the China Daily later reported that the Great Wall can be seen from space with the naked eye, under favorable viewing conditions, if one knows exactly where to look. I have walked the Great Wall at Badaling. I just love it! And it is really great! You have to see it and walk on it to understand how large it is. The feeling is overwhelming and the beauty of what you see is astonishing! So crazy!Zai jian!
Peter
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