The Great Wall of China is the world's longest human made structure. It is approximately 4000 miles
long and 26 feet high from
Shanhaiguan in the east to
Lop Nur in the west.
It has been estimated that 2 to 3 million Chinese died as part of the long project of building the wall.
The Great Wall was built between 5th century BC and the 16th century to protect the northern borders of the
Chinese Empire during the rule of successive dynasties.
The primary purpose of the wall was to insure that semi-nomadic people on the outside of the wall couldn't cross
with their horses or return easily with stolen property.
The wall has watch towers, which were used to store weapons, house troops, and send smoke signals.
One of the most interesting facts about The Great Wall of China is that astronauts claim to be able
to see it from space. In fact, the wall is clearly visible in satellite photographs of China.