The Great Wall is one of the largest
building construction projects ever completed. It
stretches across the mountains of northern China,
winding north and northwest of Beijing. It is constructed
of masonry, rocks and packed-earth. It was over 5,000
km (=10,000 Li) long. Its thickness ranged from about
4.5 to 9 meters (15 to 30 feet) and was up to 7.5
meters (25 feet) tall.
The Great Wall can be seen from Earth
orbit, but, contrary to legend, is not visible from
the moon, according to astronauts Neil Armstrong,
Jim Lovell, and Jim Irwin.
