The Great Wall of China
Early emperors had built walls in the northern territories to protect their nation against attack from outside forces. These walls were spread across the landscape, and not connected. Qin was an ambitious leader. He ordered his people to connect the existing walls together, and to expand them, eventually covering a distance of over 4000 miles. As seen in this map.
Over 300,000 peasants were forced to help build the Great Wall of China. Many of which died during the construction. After working for several years, the Great Wall of China was completed, and still stands today as one of the great building projects in human history.