The Great Wall of China
It's more than 2,000 years old, but the Great Wall of China remains one of the greatest wonders of the world, an engineering feat rarely matched in the 22 centuries since its construction began. Stretching 4,500 miles, from the mountains of Korea to the Gobi Desert, it was first built to protect an ancient Chinese empire from marauding tribes from the north. It is actually a series of walls built and rebuilt by different dynasties over 1,000 years while they often served the same purpose. It has also evolved into something far greater -- a boon to trade and prosperity and ultimately a symbol of Chinese ingenuity and will. If the great wall were built in a straight line, it could stretch from Miami, Florida to the North Pole.