Great Wall of China blueprint graphic

Classic Projects: Great Wall of China

You can't see it from space, but the Great Wall of China is undoubtedly one of humankind's greatest construction achievements.

Contrary to popular opinion you can't see it from space, but the Great Wall of China is undoubtedly one of humankind's greatest construction achievements.

According to one set of statistics, if you were to use all of its bricks to build a wall around the equator, the Great Wall of China would still be a metre wide and two metres tall. This might be an exaggeration, but there is little wonder that is has been called one of the greatest civil engineering projects of all time.

In fact, the wall is several projects, spanning centuries and millennia. Although it's virtually impossible to come up with agreement over its unit cost, economists think that to build something comparable today would cost £300bn. Others compare it with the construction of the UK's road networks over the past four decades.

Whichever way we break the project down, it is truly enormous and there will surely never be a need to build anything on this scale again.

An easier question to answer is why the wall was built in the first place. Spanning an east-west arc that roughly equates to the southern edge of Inner Mongolia today, the wall was originally a military defence designed to protect the early states of what we now know as China from invasion by northern tribes. We also know that the arrangement of walls served as a communications network, allowing smoke and other signals to be transmitted over hundreds of miles. At times it has been a border control for international traders along the Silk Road, while also acting as a trade conduit in its own right.

Construction started as early as 7th Century BC when the 'wall' comprised mostly of earthworks. For the next two millennia the project ebbed and flowed with the political situation – neither the Tang nor the Song dynasties contributed to the defensive structure.

Work on what we now regard as the Great Wall did not begin in earnest until the Ming Dynasty of the 14th century. By this time bricks were the main construction material, which allowed for the inclusion of 25,000 watchtowers. As Mongol incursions increased from the north, the wall became more fortified and it is largely due to this heavy fortification that we are left with much of the structure as we know it today. As recently as 2009 a previously unknown 180-mile section was discovered in the Liaoning Province.

The key concern for the Chinese government is over the Wall's state of disrepair. Quite apart from human activity – the wall has been plundered for centuries as a source of building materials – it is now known that wind erosion is playing a big part in its deterioration. Sandstorms have reduced part of the Wall at Ganzu to 2m in height, while heavy rain has recently washed away a 30m mud section in the Hebei province.

However, increased tourism could actually help to conserve the structure. The wall means big business and, as a result, many sections are being restored. In 2007 it was officially listed as one of the New Seven Wonders of the World, an honour that is set to earn China £5bn in increased tourism, and which inspired the 2009 visit from US President Barack Obama.

The wall has an allure that has inspired thinkers and artists. French philosopher Voltaire, while uncertain as to what the point of such a construction might be, thought that by comparison the Pyramids at Giza were 'childish'. Franz Kafka wrote a collection of stories under the name 'The Great Wall of China', and German electronic band Tangerine Dream released an album of the same name in 2000. You can even run a marathon along it on 13 May 2013.

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