The largest man-made structure in the world, the Great Wall once stretched more than 4,500 miles (7,300 kilometers) from the Jiayu Pass in Gansu Province in the west to the mouth of the Yalu River in Liaoning Province in the east. The ravages of time and vandalism have reduced it to 1,500 miles (2,400 kilometers). It has been called an “engineering marvel of stone, earth and brick.”
From 475 to 221 b.c., there were seven warring states in Chou dynasty, China—Qi, Chu, Han, Wei, Qin, Yan, and Zhao. The borders of the latter three were frequently plundered by the nomadic Xiongnu (Huns) and Donghu tribes, so they built high earth walls as a defense against them. For their part, the remaining states took similar action, fearing attacks from their capricious neighbors. Soon after he had unified China in 221 b.c., the first emperor, the despotic Ch’in Shi Huangdi, set about reinforcing his defenses against the Xiongnu by joining four earlier fragmentary walls and building new sections to extend them to 3,100 miles (5,000 kilometers). In 214 b.c. he sent General Meng Tien, with an army of 300,000 conscripted workers and countless prisoners, to the northern frontiers of his empire to begin the building the Great Wall. Garrisons of soldiers along the wall served a double purpose: they stood guard over the workers and defended the northern boundaries. Much of the Ch’in wall was constructed with dry-laid local stone, but in remote places, where stone was unavailable, the builders used earth, compacted in 4-inch-thick (10-centimeter) layers. Watch-towers were spaced two bow shots apart.
Ch’in Shi Huangdi’s policies of heavy taxation and forced labor to pay for foreign wars, the Wall, and other extravagant public works inevitably created social unrest. When he died in 210 b.c., his empire collapsed. Following years of chaos, the Han dynasty (206 b.c.-a.d. 220) was founded. Under Wu-Di (reigned 140–87 b.c.), the Han expanded into southern China, Vietnam, and Korea and opened trade routes through the wilderness of central Asia to India, Persia, and the Western world. Wu-Di controlled the Xiongnu incursions by invading their lands south of the Gobi Desert and colonizing the region with his own people. That strategy, incidentally, forced the Huns to move westward, part of a chain reaction that eventually brought about the demise of the Roman Empire. To protect what he had gained, Wu-Di inaugurated the third major phase of the Great Wall. He restored the Ch’in wall—neglected for years, the earthen parts had begun to collapse—and extended it 300 miles (280 kilometers) across the Gobi Desert. Han builders corrected the problem of the sandy soil by reinforcing the compacted earth with willow reeds. They also built beacon towers at 15- to 30-mile (25- to 50-kilometer) intervals and used smoke signals to warn of attack. All trade routes passed through the Wall.
The final construction phase, which gave the Wall its present form, was undertaken early in the Ming dynasty (1368–1644). Having finally expelled the harassing Xiongnu and their Mongol rulers, the Ming emperors set about securing their empire. They repaired and enlarged the Wall, constructing extensions of tamped earth between kiln-fired brick facings across some of China’s most mountainous terrain. The Ming wall averaged 25 feet (7.6 meters) in height; it was 15 to 30 feet (4.5 to 9 meters) thick at the base, sloping to 12 feet (3.7 meters) at the top. The watchtowers were redesigned and cannon, bought from the Portuguese, were strategically deployed.
For all its size and splendor, the Great Wall seems to have been a functional failure, with little military value. Only when China was weakened internally were northern invaders—the Mongols (Yuan dynasty) in 1271 and the Manchurians (Qing dynasty) in 1644—able to seize power without engaging in an attenuated war. Since the seventeenth century parts of the Great Wall have been quarried for their brick or stone; others have simply crumbled, while those in marshy areas have been buried by silt. Two stretches—the Badaling and Mutianyu sections—north of Beijing have been reconstructed and opened as a tourist attraction. In 1979, the Chinese government declared it a National Monument, establishing a commission to oversee its preservation; in 1987 it was inscribed on UNESCO’s World Heritage List.