Great Wall of China is the longest structure ever built. It was erected entirely by hand. The main part of the wall is about 3,460 kilometres long. One of the highest sections of the Great Wall, on Mount Badaling, near Beijing, rises to about 11 metres high. This section is about 7.5 metres wide at its base and nearly 6 metres at the top. Watchtowers stand about 90 to 180 metres apart along the wall.
We know from the text that Great Wall is ....