Your turn
Each lab is one part of the video. Drag, tap and slide, and see what happens.
Each lab isolates one idea. The map and the relay are simplified teaching models, not to scale.
Tap the buttons and slide the sliders.
Drag the globe. How far round the equator do all the walls reach? And just the Ming wall?
The 2012 survey added up the known surviving sections from every period (about 21,196 km). The Ming wall alone is about 8,850 km.
Spin the Earth with your finger. The wall goes more than halfway round!
Tap the gate. When it's shut, riders are slowed. When it's open, traders can pass and be checked.
A wall didn't seal the frontier. It slowed raids and channelled trade and travel through gates, where goods could be checked and taxed.
Tap the gate to open it or shut it. Who can come through?
Slide through time. Which dynasty built walls where?
Warring States walls, the Qin linking project (from c. 214 BCE), the Han extension west, and the Ming rebuild (1368–1644).
Simplified map, not to scale. Wall lines are approximate.
Pour in damp soil, then pound it. Each packed layer is only about 7 to 10 cm thick.
Earth is poured into a board frame and compacted with rammers; each layer is about 7–10 cm thick.
Tap the button to pound the dirt. Watch the wall grow!
Light the first tower, then switch between day and night. Smoke by day, fire by night.
Each tower was within sight of the next, so a signal could be relayed far faster than a rider.
Light the first tower. Then try day and night!
The relay speed here is for show, not real timings.
Slide out into space. When does the wall disappear?
A wall about 6 m wide, seen from the Moon (about 384,000 km), is like a 0.1 mm hair seen from about 6 km.
Slide far, far away. Can you still see the wall?
The hair comparison is rounded.
The Great Wall of China is a very, very long wall. It winds over hills, grass and deserts in the north of China.
Long ago, farmers lived on one side. They grew food and lived in villages. On the other side, on big grassy plains, herders rode horses and looked after sheep. They lived in round felt tents.
Farmers and herders often traded things. But sometimes riders came to take things from the farms. So people built walls to slow the riders down. Gates let traders through.
Builders put damp dirt in a wooden box and pounded it until it was hard as rock. Layer on layer, the wall grew. Later, builders used bricks, and even mixed sticky rice into the paste that holds the bricks together!
Towers stood along the wall. When guards saw raiders coming, they made smoke in the day and fire at night. The next tower copied it, and the message raced along the wall.
The Great Wall was built mainly to protect the farming lands of northern China from raids by horse-riding peoples of the northern grasslands, such as the Xiongnu and, much later, the Mongols.12 It also did three other jobs: its gates and forts let guards control trade and travel across the frontier and tax goods,911 its beacon towers passed warnings along the line with smoke by day and fire by night,510 and it marked the edge of the empire.
The big surprise is that the Great Wall isn't one wall. It is many walls, many of them running side by side, built and rebuilt by different Chinese states and dynasties over about 2,000 years.1
For thousands of years, northern China was where two very different ways of life met. To the south, farmers grew crops and lived in villages and walled towns. To the north, on the open grassland called the steppe, nomadic herders moved several times a year to find water and grass for their horses, sheep and other animals, living in round felt tents.13 UNESCO describes the Great Wall as a record of both "collision and exchanges" between farming and nomadic civilisations.2
The two sides often traded, and in hard times herders depended on goods from China.13 But there were also raids. Mounted riders could strike quickly, and fast horses were hard to stop on open ground.14 A wall didn't make a frontier impossible to cross, but it slowed riders down, gave guards time to react, and funnelled people and goods through gates where they could be checked.
Different rulers built different walls, in different places, with different materials. Here are the big chapters.129
| Period | When | What happened |
|---|---|---|
| Rival states | c. 7th–3rd century BCE | States such as Chu, Qi, Yan, Zhao and Qin built walls against each other and against northern peoples. |
| Qin dynasty | 221–206 BCE | The first emperor, Qin Shi Huang, united China in 221 BCE. From about 214 BCE, General Meng Tian linked the northern walls of Qin, Yan and Zhao against the Xiongnu. |
| Han dynasty | 206 BCE – 220 CE | Extended walls far to the west into Gansu, guarding the trade routes later called the Silk Road. Rammed-earth Han walls still survive there. |
| Later dynasties | 4th–14th century | Some dynasties (including the Northern Wei, Liao and Jin, founded by northern peoples) built their own walls; others, like the Tang and Song, built little. |
| Ming dynasty | 1368–1644 | After long conflict with Mongol groups, rebuilt the wall in brick and stone with many watchtowers. This is the wall in most photos. |
| Qing dynasty | 1644–1912 | Qing rule reached into Inner Mongolia, so the wall mattered much less for defence. |
Qin Shi Huang is often called the builder of the Great Wall, but very little of his wall survives. The famous brick sections near Beijing, such as the ones visitors walk on today, are Ming.411
It depends what you count. In 2012 China's State Administration of Cultural Heritage published a survey that added up every known surviving section from every period: about 21,196 km (13,171 miles), spread over 15 provinces and regions.3 That's more than half the distance around Earth's equator (about 40,075 km).12 The Ming wall alone is about 8,850 km (5,500 miles) long.13 About a quarter of the Ming line is made up of natural barriers such as rivers and mountain ridges rather than built wall.1
Builders almost always used what was close by, because carrying materials over mountains and deserts was so hard.59
Some Ming mortar had a surprising ingredient: sticky rice soup, mixed into slaked lime. Chemists led by Yang Fuwei and Zhang Bingjian studied old mortar and found that amylopectin, a starch from sticky rice, helped make it stronger and more water-resistant than lime mortar alone.78
Under the Qin, the work was done by soldiers, farmers called up for a period of service, and convicts, hundreds of thousands of people in all.15 Most things were moved by people: on their backs, on shoulder poles, or passed hand to hand up steep slopes.5 The work was hard and dangerous, and the wall appears in many Chinese poems and stories about hardship and separation.2
A wall only helps if the defenders know where trouble is. So beacon towers were built at passes, river bends and road junctions, each within sight of the next.5 When guards saw raiders coming, they sent a signal: smoke in the daytime, fire at night.10 The next tower copied it, and the warning travelled along the chain much faster than a rider could. Flags and drums were used too.5 In the beacon lab above, the relay speed is just for show; it isn't based on real timings.
Partly. It was never a line nobody could cross. The Mongols conquered all of China in the 13th century, before most of the Ming walls existed, and the Ming then built much stronger walls because of continuing conflict with Mongol groups.9 In 1644 the Manchus came through Shanhai Pass, the wall's great eastern gate, because a Ming general opened the gates to them.9 What the wall did well was slow down small raids, give warning, and control everyday traffic and trade across a very long frontier.
Take a small, clean food carton, like a juice or milk carton, and cut off the top (ask an adult to help with the scissors). Mix garden soil with a little sand and just enough water to make it damp, not muddy. Add a layer about 2 cm deep, pound it hard with the end of a wooden spoon, then add the next layer. After 6 to 8 layers, let it dry for a few days and peel the carton away. You'll see stripes, one for each layer, just like on real rammed-earth walls. Wash your hands afterwards.
Want more ancient engineering? See how the pyramids were built, or find out why the Roman Empire fell, another empire that guarded a long frontier.
Mainly to protect farming lands in northern China from raids by horse-riding peoples of the northern steppe, such as the Xiongnu and later the Mongols. It also let guards control who and what crossed the frontier, tax trade, and pass warnings along chains of beacon towers.
Defence was the main purpose, but not the only one. Gates and forts controlled trade and travel, beacon towers sent signals by smoke and fire, and the walls marked the edge of the empire. Historians describe the frontier as a place of both conflict and exchange between farmers and herders.
Many states and dynasties over about 2,000 years. The work was done by soldiers, farmers called up for service, and convicts. Qin Shi Huang linked older walls around 214 BCE, the Han extended them west, and the Ming built most of the famous brick sections from 1368 to 1644.
There was no single build. Walls were started around the 7th century BCE and building went on, on and off, until the Ming dynasty ended in 1644. The Qin linking project alone began about 214 BCE and lasted around a decade.
A Chinese government survey published in 2012 measured all known surviving sections from every period at about 21,196 km (13,171 miles). The Ming wall alone is about 8,850 km (5,500 miles).
The Mongols conquered China in the 13th century, before most of the Ming walls we see today had been built. The Ming then built much stronger walls because of continuing conflict with Mongol groups. In 1644 the Manchus passed the wall at Shanhai Pass after a Ming general opened the gates to them.
Not from the Moon, and not with the naked eye from orbit either. NASA says it is difficult or impossible to see from the space station without a powerful lens, because it is only a few metres wide and the same colour as the land around it.