The name Great Wall covers walls, passes, and beacon towers from different eras and regions. It is not one complete stone wall built by a single emperor in a single project.

Ming walls are prominent at many tourist sites, but earlier forms included rammed earth. The border defense system also involved garrisons, communication, and transport management.

Ming and Qing eras

The Ming dynasty made substantial contributions to the Great Wall, following their defeat to the Oirats in the Battle of Tumu. This defeat had come in the context of protracted conflict with Mongol tribes; a new strategy for defense was thus realized 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. Under general Qi Jiguang's supervision, 1,200 watchtowers from Shanhaiguan Pass to Changping were constructed between 1567 and 1570, and sections of the ram-earth wall were faced with bricks.

During the mid–15th century, the Ming also built a so-called "Liaodong Wall". It enclosed the agricultural heartland of the Liaodong province, protecting it against potential incursions by Jurchen-Mongol Oriyanghan from the northwest and the Jianzhou Jurchens from the north. While stones and tiles were sometimes used here, it was otherwise 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 short-lived Shun dynasty. 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 instead, and eventually defeated both the Shun dynasty and the remaining Ming resistance, consolidating the rule of the Qing dynasty over all of China proper.

Under Qing rule and the annexation of Mongolia into the empire, China's borders extended beyond the Great Wall; work on it for the purpose of border defense was thus discontinued. Construction nevertheless persisted with projects like the Willow Palisade; following a line similar to that of the Liaodong Wall of the Ming, it was meant to prevent Han Chinese migration into Manchuria.

Han Great Wall

Han fortifications start from Yumen Pass and Yang Pass, southwest of Dunhuang, in Gansu province. Ruins of the remotest Han border posts are found in Mamitu (t, s, Mǎmítú, l "horses losing their way") near Yumen Pass.

Ming Great Wall

The Jiayu Pass, located in Gansu province, is the western terminus of the Ming Great Wall. From here, 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 cut through the Ordos Desert to the eastern edge of the Yellow River loop. There, at Piantou Pass (t, s, Piāntóuguān) in Xinzhou, Shanxi, the Great Wall splits in two with the "Outer Great Wall" (t, s, Wài Chǎngchéng) extending along the Inner Mongolia border with Shanxi into Hebei province, and the "Inner Great Wall" (t, s, 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 (Sìhǎiyě), in Beijing's Yanqing County.