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, featuring walls, trenches, and natural barriers. Made from various materials like earth, wood, bricks, and stone, the wall varies in height and width. It served not only as a defense mechanism but also as a means of controlling trade and immigration along the Silk Road. Today, it is a UNESCO World Heritage Site and a symbol of China's historical strength.