The longest man-made structure on Earth

Dear Diary,

Today we are at our last destination in our journey through the modern World Wonders. Guide Bird and our crew were quite enthusiastic about visiting this wonder of China. When we talk about China, the first thing that comes to mind is the Great Wall. So, that is what we went to see today.

Did you know that the Great Wall is the world's longest human-made structure? It stretches over 6,400 kilometres, from Shenanigan in the east to Lop Nur in the west, along an arc that roughly outlines the southern edge of inner Mongolia. It is also the largest human-made structure ever built in terms of surface area and mass.

It is said that the Great Wall can be seen from the Earth's orbit, but contrary to popular belief, is not visible from the Moon, according to astronauts Neil Armstrong, Jim Lovell and Jim Irwin.

It was made a UNESCO World Heritage Site in 1987.

The Great Wall of China was built over 2,000 years ago, by Qin Shi Huangdi, the first emperor of China during the Qin (Chin) period (221 B.C - 206 B.C.). In Chinese, the wall is called 'Wan-Li Qang-Qeng' which means 10,000-Li long wall.

After conquering and uniting China from seven warring states, the emperor connected and extended four old fortification walls along the north of China that originated in about 700 B.C. (over 2500 years ago). Armies were stationed along the wall as a first line of defence against the invading nomadic Hsiung Nu tribes north of China (the Huns). Signal fires from the Wall provided early warning of an attack.

The Great Wall is one of the largest building construction projects ever completed. It is constructed of masonry, rocks and packed earth. Its thickness ranged from about 4.5 to nine metres and was up to 7.5 metres tall.

During the Ming period (1368-1644), the Great Wall was enlarged to 6,400 kilometres (4,000 miles) and renovated over a 200-year period, with watchtowers and cannon added.

The wall also has watchtowers at regular intervals, which were used to store weapons, house troops, and send smoke signals. Barracks and administrative centres were located at larger intervals.

Communication between the army units along the length of the Great Wall, including the ability to call support and warn garrisons of enemy movements, was of high importance. Signal towers were built upon hilltops or other high points along the wall for their visibility. Before the use of bricks, the Great Wall was mainly built from soil, stones, and wood.

During the Ming period however, bricks were heavily used in many areas of the wall, as were materials such as tiles and limestone. The size and weight of the bricks made them easier to work with than earth and stone, so construction quickened.

Additionally, bricks could bear more weight and endure more than packed earth. Stones could hold weight better than bricks, but were more difficult to use. Consequently, stones cut in rectangular shapes were used for the foundation, inner and outer edges, and gateways of the wall. Battlements lined the main part of the vast majority of the wall, with defensive gaps a little over 30 cm tall and about 23 cm wide.

The steps that form the Great Wall of China are very steep and tall in some areas. Tourists often become exhausted climbing the wall, and walk no more than a kilometre or two at a stretch.

Now, most parts of the Great Wall are not renovated and are in ruins. However, there are some sections in the Beijing municipality, which have been renovated and which are regularly visited by tourists.

The "North Pass" of Juyongguan pass is a section which is most visited by tourists. This section of the wall used to have many guards in the past to defend China's capital, Beijing. Made of stone and bricks from the hills, this portion of the Great Wall is 7.8 metres high and five metres wide. One of the most striking sections of the Ming Great Wall is where it climbs extremely steep slopes.

It runs 11 kilometres long, ranges from five to eight metres in height, and is six metres wide across the bottom, narrowing up to five metres across the top.

All of us felt rather tired after flying across the length and breadth of the Wall, so we decided to call it a day.

See you next time from another wonderful place. Until then, bye!

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