Great Wall (China), popular name for a semi-legendary wall built to protect China’s northern border in the 3rd century bc, and for impressive stone and earthen fortifications built along a different northern border in the 15th and 16th centuries ad, long after the ancient structure had mostly disappeared. Ruins of the later wall are found today along former border areas from Bo Hai (a gulf of the Yellow Sea) in the east to Gansu Province in the west. The Great Wall is visited often near Beijing, at a site called Ju-yong-guan, and at its eastern and western extremes.

The Great Wall is probably China's best-known monument and one of its most popular tourist destinations. In 1987 it was designated a World Heritage Site by the United Nations Educational, Scientific and Cultural Organization (UNESCO). The Great Wall is not a single, continuous structure. Rather, it consists of a network of walls and towers that leaves the frontier open in places. Estimates of the total length of the monument vary, depending on which sections are included and how they are measured. The Great Wall is about 2,400 km (about 1,500 mi) long, according to conservative estimates. Other estimates cite a length of 6,400 km (4,000 mi), or even longer. Some long-standing myths about the wall have been dispelled in recent decades. The existing wall is not several thousand years old, nor is it, as has been widely asserted, visible with the naked eye from outer space. (Astronauts have confirmed this. However, some of the wall is discernible in special radar images taken by satellites.)