Sometime in the 14th century, the first Mexica found their way into the valley of Teotihuacán. The Mexica (often incorrectly called Aztecs in modern times) were new to the region. An aggressive, ambitious people from the north, they were fast becoming the dominant force in highland Mexico, conquering territory and setting up the powerful city of Tenochtitlán, which would soon rule a massive empire from what is now called Mexico City. Imagine that first search party—bold, feeling invincible as a nascent superpower—coming into a lush green expanse surrounded by rolling hills. The warriors are following tales told by the local Toltec tribes of a place in the mountains, just 25 miles from their new home, where the gods once lived. Then, turning a bend, their bravado gives way to awe as the home of the gods looms into view. Ruins of pyramids as high as 20 stories—so big they are initially mistaken for hills—line a huge road. Everywhere the explorers look lie crumbling temples, marketplaces and relics of a long-dead civilization with no name, no writing, no history. Just a vast city, once glorious beyond imagination, now abandoned.