The first formal measurement of the Great Wall of China in 2012 revealed that the wall is 13,17 miles long, a number that includes all of its branches. This is more than twice as long as previously thought based on historical records.
Several of the walls that would eventually be connected to form the Great Wall were built as early as the seventh century B.C. The wall was built to protect the Chinese empire from invasion by various nomadic and warlike people. The main part of the Great Wall stretches from Shanhaiguan in the east to Lop Lake in the west.