The main Great Wall of China stretches approximately 5,500 miles along the southern edge of Inner Mongolia. Explorer experts state that it takes 18 months to walk its entire length. It was constructed during the Ming dynasty in the 14th and 15th century, and is sometimes called the Ming Wall.
The Ming Great Wall is only one of many built by the Chinese as a defense against foreign invaders. The wall was never a single continuous structure, but rather a network of wall segments built at various times, using a variety of construction techniques. Contrary to popular legend, it cannot be seen with the unaided eye from the moon. It is visible from a low Earth orbit, as are many large, man-made structures.