How big is Great Wall of China? | Scale of the Universe

The Great Wall of China is a chain of walls, watchtowers and forts built across northern China over about 2,000 years. UNESCO describes it as running from Shanhaiguan in the east to Jiayuguan in the west, two places about 1,800 kilometers (1,100 miles) apart in a straight line. Because it is made of many separate sections, its full length is far greater. A Chinese government survey announced in 2012 measured 21,196 kilometers (13,171 miles).

Size

The Great Wall is not one wall but many, built by different dynasties, or ruling families, along China's old northern border. UNESCO has listed the wall as a World Heritage site since 1987. It describes the wall as beginning at Shanhaiguan in Hebei province and ending at Jiayuguan in Gansu province. Using the map coordinates UNESCO gives for those two places, the straight-line distance between them is about 1,800 kilometers.

Measured along every section, the wall is much longer. China's State Administration of Cultural Heritage surveyed it from 2007 and announced in 2012 that its sections add up to 21,196.18 kilometers. A preliminary result released in 2009 had given 8,850 kilometers, and UNESCO now gives a total of more than 20,000 kilometers. Before the survey, estimates of the length came mainly from historical records.

Size comparisons

From end to end, the wall spans about one and a half times the east–west width of Texas.
The straight line between its ends is about four-fifths the length of the Great Barrier Reef, which stretches about 2,300 kilometers.
All its sections together would reach more than halfway around Earth, which measures 40,075 kilometers (24,901 miles) around the equator.
The full length of the wall is more than 11 times the straight-line distance between its ends.
About 500 marathons, each 42.195 kilometers (26.2 miles) long, laid end to end would match the wall's full length.

Many walls, many dynasties

Walls to keep out invaders from the north were built in China for centuries before the country was united. Around 220 BC, under the first emperor, Qin Shi Huang, sections of earlier walls were joined into one defensive system. Later dynasties rebuilt and extended it until the Ming dynasty (1368–1644), when, according to UNESCO, the Great Wall became the largest military structure in the world.

Besides the walls themselves, the Great Wall includes watchtowers, shelters, horse tracks, forts and passes. Early sections were made mostly of rammed earth (soil and stones packed hard) and wood. Later builders also used brick and cut stone. The 2012 survey counted 43,721 sites belonging to the wall, and reported that only 8.2 percent of the original wall remains intact.

Seen from space

A popular claim says the Great Wall can be seen from the Moon, which is about 384,400 kilometers (238,900 miles) away, but it cannot. The claim appeared in a Ripley's cartoon in 1932, and it still appears in UNESCO's description of the site. Even from low orbit, which begins about 160 kilometers (100 miles) up, the wall is hard to pick out. Its stone and clay are close in color to the land around it.

The wall shows up from orbit only in some conditions, such as when a low Sun makes it cast long shadows. China's first astronaut, Yang Liwei, told reporters after his 2003 flight that he had not seen it. In 2004 Leroy Chiao photographed part of it from the International Space Station through a powerful lens, and NASA experts later confirmed that the photo appears to show the wall.