Explanation:
The Great Wall of China is the longest man-made structure in the world. It stretches over approximately 13,170 miles (21,196 kilometers) and was built over several dynasties, with construction starting as early as the 7th century BC. The primary purpose of the wall was to protect Chinese states and empires from invasions and raids by nomadic tribes from the north. The wall is made up of various materials, including earth, wood, bricks, and stones, and features watchtowers, barracks, and fortresses along its length. Its vast scale and historical significance make it one of the most remarkable architectural feats in human history.