<P> When China opened its borders to foreign merchants and visitors after its defeat in the First and Second Opium Wars, the Great Wall became a main attraction for tourists . The travelogues of the later 19th century further enhanced the reputation and the mythology of the Great Wall, such that in the 20th century, a persistent misconception exists about the Great Wall of China being visible from the Moon or even Mars . </P> <P> Although a formal definition of what constitutes a "Great Wall" has not been agreed upon, making the full course of the Great Wall difficult to describe in its entirety, the course of the main Great Wall line following Ming constructions can be charted . </P> <P> The Jiayu Pass, located in Gansu province, is the western terminus of the Ming Great Wall . Although Han fortifications such as Yumen Pass and the Yang Pass exist further west, the extant walls leading to those passes are difficult to trace . From Jiayu Pass the wall travels discontinuously down the Hexi Corridor and into the deserts of Ningxia, where it enters the western edge of the Yellow River loop at Yinchuan . Here the first major walls erected during the Ming dynasty cuts through the Ordos Desert to the eastern edge of the Yellow River loop . There at Piantou Pass (t 偏 頭 關, s 偏 头 关, Piāntóuguān) in Xinzhou, Shanxi province, the Great Wall splits in two with the "Outer Great Wall" (t 外 長城, s 外 长城, Wài Chǎngchéng) extending along the Inner Mongolia border with Shanxi into Hebei province, and the "inner Great Wall" (t 內 長城, s 內 长城, Nèi Chǎngchéng) running southeast from Piantou Pass for some 400 km (250 mi), passing through important passes like the Pingxing Pass and Yanmen Pass before joining the Outer Great Wall at Sihaiye (四海 冶, Sìhǎiyě), in Beijing's Yanqing County . </P> <P> The sections of the Great Wall around Beijing municipality are especially famous: they were frequently renovated and are regularly visited by tourists today . The Badaling Great Wall near Zhangjiakou is the most famous stretch of the Wall, for this is the first section to be opened to the public in the People's Republic of China, as well as the showpiece stretch for foreign dignitaries . South of Badaling is the Juyong Pass; when used by the Chinese to protect their land, this section of the wall 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 m (25 ft 7 in) high and 5 m (16 ft 5 in) wide . </P>

Where is the the great wall of china located
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