The Great Wall of China is a series of fortifications built to protect Chinese states from invasions. Construction began as early as the 7th century BC and continued for centuries, with the most famous sections built during the Ming Dynasty (1368-1644). The wall stretches over 13,000 miles across northern China, showcasing various materials like earth, wood, bricks, and stone. The wall is not a single continuous structure but rather a collection of walls and trenches. It features watchtowers and barracks for soldiers, allowing for communication and defense. Today, the Great Wall is a UNESCO World Heritage Site and a popular tourist attraction, symbolizing China's historical strength and resilience.