These are some of the world's greatest monuments. They combine colossal mass with precision engineering. For over 4,000 years they were unsurpassed, yet they were built by peasant societies with only simple tools. And the Egyptians weren't alone. From China to the Americas, pyramids were the crowning achievements of other civilizations around the world. While searches for treasure have always brought thieves and bounty hunters to the pyramids, the challenge for today's explorers is to reveal the amazing stories of the people who built them.