Not one wall, but many
The phrase “Great Wall of China” suggests one continuous structure built by one emperor. The real history is more varied. Different states and dynasties built, rebuilt and abandoned long stretches of wall over some two thousand years, in different materials and in different places. A government survey published in 2012 reported a combined length of about 21,000 kilometres for all surviving wall sections of all periods, and gave roughly 8,800 kilometres for the Ming dynasty portions. These are approximate figures, and the counts change as new sections are identified.
The popular belief that the wall can be seen from space is a myth. Long stretches are narrow and made of materials that match the landscape.
Early walls and Qin
Warring States kingdoms, including Qi, Wei, Zhao, Yan, Chu and Qin, built defensive walls along their borders, mostly of rammed earth. Early wall building was therefore regional and aimed as much at neighbouring Chinese states as at nomads. After the Qin conquest, the First Emperor is traditionally said to have sent the general Meng Tian north with a large force around 214 BCE, with orders to drive back pastoral peoples and link up older northern walls into a defence line. Historians accept that Qin improved and joined northern fortifications, but little of what survives can be certainly attributed to Qin construction. Descriptions of a single wall running across the whole north belong to a later tradition.
Han walls in the desert
The Han dynasty extended walls far to the west, along the Hexi Corridor in Gansu and beyond, to protect farming settlements and the routes that later developed into the Silk Road trade routes. The Han also faced the Xiongnu confederation, and the garrison towns and signal towers formed part of a frontier system.
The building method changed with the landscape. In desert areas, where good clay was scarce, builders used layers of reeds, tamarisk branches and gravel, bound with sand and clay, and some of these structures still survive. Beacon towers, spaced at intervals, allowed smoke and fire signals to carry warnings along the line. Texts on wooden slips from Han garrison sites describe the daily life of soldiers, supplies and signals, and provide evidence that the wall was part of a living military system.
Rammed earth
The basic technique in many periods was hangtu, or rammed earth. Builders set wooden frames and filled them with thin layers of earth, which workers pounded down with heavy tools until compact. Layers were often only a few centimetres deep, and the repeated tamping made a hard, durable core. It is cheap, uses local material and can be done by large labour crews. Such walls erode slowly, but weather and neglect have worn many of them down to low ridges.
Northern dynasties, Sui and Jin
Several later dynasties added their own walls. States of the north in the 5th and 6th centuries CE rebuilt long sections, and the Sui dynasty repaired and extended walls using large labour levies. The Jin dynasty from the 12th century built border works of its own. Each project reflected a different political situation, and some walls were not placed to keep out nomads at all but to control movement or mark territory.
The Ming wall
The brick and stone Great Wall of the postcards is mostly a Ming construction, built from the later 15th century and especially in the 16th. The Ming rulers had expelled the Mongol Yuan dynasty in 1368 and faced continuing Mongol pressure on the northern frontier. After a serious defeat in 1449, they put more resources into fixed defences, a policy that went hand in hand with a wider Ming restoration of Chinese rule. Building and rebuilding went on for generations.
Ming engineering was more elaborate than earlier work.
- Materials. Fired bricks and cut stone faced a core of earth and rubble. Kilns were set up near building sites. Mortar made with lime was used, and some studies have reported an additive of sticky rice starch in certain sections, although how widespread this was is not clear.
- Design. Walls were built to follow ridges and mountain crests, with parapets and crenellations on the outer side and a walkway on top wide enough for patrols.
- Towers. Watchtowers and, in some regions, hollow towers that could shelter garrisons and store weapons were built at regular intervals. Commanders such as Qi Jiguang are associated with the improved tower designs in the north-east.
- Passes. Fortified gates at points such as Shanhaiguan, Juyongguan and Jiayuguan controlled the main routes and gave the wall its practical purpose.
Builders and labour
The labour came from soldiers, conscripted peasants and, at times, convicts. Working conditions were hard, and the folk tradition about people who died during construction reflects real hardship, even though the details of the legends are not history. Costs were paid in taxes, grain and manpower.
Did it work?
Walls were not designed as impassable barriers. They slowed raiders, supported patrols, allowed signalling and made trade and movement easier to regulate. They also failed at times. In 1644 the Ming general Wu Sangui opened Shanhai Pass to the Manchu forces, which then entered China and founded the Qing dynasty. Armies that were determined, or invited, could cross, and the wall depended on garrisons and politics as much as on stone.
Understood in this way, the Great Wall is less a single monument than a long record of how Chinese states managed their northern frontier. Some parts have been restored for visitors, while others are collapsing, so what a tourist sees on different stretches can be very different in age and construction.