Mutianyu Great Wall

　　 The Great Wall was key to protecting agriculture and resisting cavalry and other warrior tribes from the north.  The advantages of the enormous barrier diminished with the advancement of gunpowder and other weaponry.

　　 The wall was originally built of stone, wood, grass and earth. In the Ming Dynasty bricks were produced in kilns set up along the wall. The bricks were  transported by men carrying them on their backs, donkeys, mules and even goats had a brick lied to their head before being driven up a mountain.

　　 The Great Wall of China was built over more than two thousand years. Construction on the first section began between the 7th and 6th century BC, and the last work on the wall was done between the 14th and 17th centuries.

Juyongguan  Great Wall

　　 There are more than 10,000 watchtowers and beacon towers on the Great Wall They were used to house troops, store weapons and send signals in case enemies were seen approaching. Smoke signals were used in the day and fires were lit at night to communicate with other military outposts along the wall.

　　 Some towers are standing complete and others are crumbling. Many have been rebuilt.

Jiankou  Great Wall

　　 The square cutouts in the top part of the wall are called crenels and were used for keeping a lookout. The smaller holes below were used for shooting arrows at the enemy.