First Emperor Qin was only emperor for 15 years. But in that time, he made great changes. It was under his rule that China became one country.
One of the things Emperor Qin wanted to accomplish was to strengthen China's protection from the Mongol tribe to the north. China's natural barriers in the east, south, and west, protected her from invasion. But China was vulnerable to the north.
Emperor Qin set people to work to build the Great Wall. Qin wanted a wall 30 feet wide and 50 feet high. This was quite an engineering feat!
Qin put many people to work building the wall including criminals, scholars, captured enemies and anyone he felt like assigning to the wall construction. Laborers who worked on the wall were not paid and they were not given very much food. It was slave labor and very harsh. People died of disease and exhaustion. There were accidents from falling rocks.
Even though Qin put over 3,000 people to work building the wall, it took a little longer than he had originally thought it would to build. It took over 1700 years! Emperor after emperor followed Qin's lead and forced people to build the wall. By the time the wall was done, it was 3700 miles long!
The Great Wall still stands. You can visit it. You can stand on it. You can see it from space!