ABOUT BEIJING

Its total population in 2013 was 21,150,000. The city proper is the 3rd most populous in the world. The metropolis, located in northern China, is governed as a direct-controlled municipality under the national government with 16 urban, suburban, and rural districts. Beijing Municipality is surrounded by Hebei Province with the exception of neighboring Tianjin Municipality to the southeast; together the three divisions form the Jingjinji metropolitan region and the national capital region of China.

Beijing is the second largest Chinese city by urban population after Shanghai and is the nation's political, cultural and educational center. It is home to the headquarters of most of China's largest state-owned companies, and is a major hub for the national highway, expressway, railway, and high-speed rail networks. The Beijing Capital International Airport is the second busiest in the world by passenger traffic.

The Chinese were already familiar with the techniques of wall-building by the time of the Spring and Autumn period between the 8th and 5th centuries bce. During this time and the subsequent Warring States period, 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.

Ming Era

The Great Wall concept was revived again under the Ming in the 14th century, and following the Ming army's defeat by the Oirats in the Battle of Tumu. The Ming had failed to gain a clear upper hand over the Mongolian tribes after successive battles, and the long-drawn conflict was taking a toll on the empire. The Ming adopted a new strategy to keep the nomadic tribes 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 Yellow River.

 Unlike the earlier fortifications, the Ming construction was stronger and more elaborate due to the use of bricks and stone instead of rammed earth. Up to 25,000 watchtowers are estimated to have been constructed on the wall. 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 strong. Qi Jiguang between 1567 and 1570 also repaired and reinforced the wall, faced sections of the ram-earth wall with bricks and constructed 1,200 watchtowers from Shanhaiguan Pass to Changping to warn of approaching Mongol raiders. During the 1440s–1460s, the Ming also built a so-called "Liaodong Wall". Similar in function to the Great Wall (whose extension, in a sense, it was), but more basic in construction, the Liaodong Wall enclosed the agricultural heartland of the Liaodong province, protecting it against potential incursions by Jurched-Mongol Oriyanghan from the northwest and the Jianzhou Jurchens from the north. While stones and tiles were used in some parts of the Liaodong Wall, most of it was in fact simply an earth dike with moats on both sides.

Towards the end of the Ming, the Great Wall helped defend the empire against the Manchu invasions that began around 1600. Even after the loss of all of Liaodong, the Ming army held the heavily fortified Shanhai Pass, preventing the Manchus from conquering the Chinese heartland. The Manchus were finally able to cross the Great Wall in 1644, after Beijing had already fallen to Li Zicheng's rebels. Before this time, the Manchus had crossed the Great Wall multiple times to raid, but this time it was for conquest. The gates at Shanhai Pass were opened on May 25 by the commanding Ming general, Wu Sangui, who formed an alliance with the Manchus, hoping to use the Manchus to expel the rebels from Beijing. The Manchus quickly seized Beijing, and eventually defeated both the rebel-founded Shun dynasty and the remaining Ming resistance, establishing the Qing dynasty rule over all of China.

Under Qing rule, China's borders extended beyond the walls and Mongolia was annexed into the empire, so constructions on the Great Wall were discontinued. On the other hand, the so-called Willow Palisade, following a line similar to that of the Ming Liaodong Wall, was constructed by the Qing rulers in Manchuria. Its purpose, however, was not defense but rather migration control.

THE NAMES OF GREAT WALL

The collection of fortifications now known as "The Great Wall of China" has historically had a number of different names in both Chinese and English.

In Chinese histories, the term "Long Wall(s)" (長城, changcheng) appears in Sima Qian's Records of the Grand Historian, where it referred to both the separate great walls built between and north of the Warring States and to the more unified construction of the First Emperor. The Chinese character 城 is a phono-semantic compound of the "place" or "earth" radical 土 and 成, whose Old Chinese pronunciation has been reconstructed as *deŋ. It originally referred to the rampart which surrounded traditional Chinese cities and was used by extension for these walls around their respective states; today, however, it is much more often simply the Chinese word for "city".

The longer Chinese name "Ten-Thousand-Mile Long Wall" (萬里長城, Wanli Changcheng) came from Sima Qian's description of it in the Records, though he did not name the walls as such. The ad 493 Book of Song quotes the frontier general Tan Daoji referring to "the long wall of 10,000 miles", closer to the modern name, but the name rarely features in pre-modern times otherwise. The traditional Chinese mile (里, lǐ) was an often irregular distance that was intended to show the length of a standard village and varied with terrain but was usually standardized at distances around a third of an English mile. Since China's metrication in 1930, it has been exactly equivalent to (500 metres or 1,600 feet), which would make the wall's name describe a distance of 5,000 kilometres (3,100 mi). However, this use of "ten-thousand" (wàn) is figurative in a similar manner to the Greek and English myriad and simply means "innumerable" or "immeasurable".

Because of the wall's association with the First Emperor's supposed tyranny, the Chinese dynasties after Qin usually avoided referring to their own additions to the wall by the name "Long Wall". Instead, various terms were used in medieval records, including "frontier(s)" (塞, sāi), "rampart(s)" (垣, yuán), "barrier(s)" (障, zhàng), "the outer fortresses" (外堡, wàibǎo), and "the border wall(s)" (t 邊牆, s 边墙, biānqiáng).[13] Poetic and informal names for the wall included "the Purple Frontier" (紫塞, Zǐsāi) and "the Earth Dragon" (t 土龍, s 土龙, Tǔlóng). Only during the Qing period did "Long Wall" become the catch-all term to refer to the many border walls regardless of their location or dynastic origin, equivalent to the English "Great Wall".