The Great Wall of China is by far the most well-known and most visited ancient wall standing today. It was built to protect what was then China's northern border. This was an ongoing construction project, with the first barriers built well more than 2,000 years ago. These original fortifications have eroded away over time. The main goal of the early and later walls was to repel invaders from the north, though in addition, the wall acted as a barrier for tax collection purposes for goods traveling on the Silk Road.
During the 14th century, the rulers of the Ming Dynasty built the sections of the wall that became known as the Great Wall. Using brick and building more than 20,000 towers, these fortifications were stronger and better defended than their predecessors. Today, people visit the sections of this Ming wall, with the parts that run along the tree-covered mountains near Beijing being the most crowded. Most people come to the wall as part of a day trip, although multiple-day guided tours are also available.