They are some of the biggest pyramids on the planet, towering above the landscape in a massive display of wealth and power. Today, they remain as centrepieces of the majestic ancient city of Teotihuacán, the first major metropolis of the Americas. The pyramids were built 2,000 years ago in Mexico by a people who have long ago vanished into myth and legend. Their purpose remains a mystery. With exclusive access to the latest finds, including DNA analysis and modern forensic examinations of ancient murder victims, National Geographic unravels the mysteries surrounding the rise and fall of one of the ancient world's most powerful - and least understood - civilizations.