The largest human-made structure on Earth is the Great Wall of China. Stretching over 13,000 miles, this monumental construction was built over centuries, primarily to protect Chinese states and empires from invasions. The wall consists of a series of fortifications made from various materials, including earth, wood, bricks, and stones. Although it is often thought of as a single continuous barrier, the Great Wall comprises many sections built by different dynasties. It serves as a symbol of China's historical resilience and engineering ingenuity and has been recognized as a UNESCO World Heritage Site since 1987.