The wall is made of cement, rocks, bricks, and powdered dirt. It was built to protect the north of the empire of China from enemy attacks. It is the longest structure humans have ever built. It is about 21,196 kilometres (13,171 miles) long, 9.1 metres (30 feet) wide and 15 metres (50 feet) high.
B.) Supplies were scarce and demand was great. Entrepreneurs provided the things the miners needed. That allowed the entrepreneurs to earn good profits.
