The largest man-made structure in the world is the Great Wall of China. Stretching over 13,170 miles (21,196 kilometers), this ancient fortification was constructed starting in the 7th century BC and continued through various dynasties until the 16th century. The Great Wall was built primarily for defense purposes, protecting Chinese states from invasions and raids. It reflects significant historical, architectural, and cultural heritage, showcasing the ingenuity and effort of millions of workers over centuries. Today, the Great Wall is a UNESCO World Heritage Site and a major tourist attraction, symbolizing China's historical strength and perseverance.