It is 5,500 miles long in total. The construction of the Great Wall initated since Waring States Perios of the Eastern Zhou Dynasty. Present Great Wall was mainly the remain of the Ming Dynasty. It is so important because it lasted so many time, play important role in pretect the state and a human-made miracle. According to our astronaut Yang Liwei's first hand experience, the Great Wall can be not seen from the Space.

it is nearly 9.000 kliometers.
it is importent because it is over 2.000 years old.