The Chinese built walls as early as 600 B.C. to keep out the enemy, during the Shang and Zhou dynasties. The construction of the Great Wall was originally started during the rule of Emperor Shi Huangdi. Shi ordered the wall to be six horses wide at the top, eight horses wide at the bottom, and five men high. The emperor ordered all of the teachers, criminals, troublemakers, pheasants, musicians, writers, and artists to build the wall. Total, about one million (1,000,000) people were sent to construct the wall. Every one hundred yards, a watchtower was to be built. Because the Chinese had not yet developed an accurate way of measuring things, the distance between towers varied by some 100 yards. From these watchtowers hung oil pans, or some way of communicating with the other towers if the enemy were to carry out a surprise attack. The Chinese wall builders worked day and night to build the walls. Many people died in the process, though. They were buried in the wall. The wall no longer used as defense mechanism, but it is a major tourist attraction, and generates millions of dollars.