The Great Wall of China has a long history, beginning as separate walls constructed by different dynasties starting in the 7th century BC to protect against invaders. The Ming Dynasty rebuilt and connected existing walls between the 14th and 17th centuries, creating the structure seen today stretching over 13,000 miles. While its defensive purposes were not always effective, over 1 million workers lost their lives constructing it, and it has since become a major tourist attraction.