With a population exceeding 24 million and urban sprawl blanketing an estimated 1,482 square kilometers, Mexico City is among the largest cities in the world—and one of the highest at an elevation of 2,240 meters. As one gazes out over the seemingly endless imprint of civilization embraced by the snow-capped peaks of the Sierra Madres, it is nearly impossible to visualize the extraordinary transformation the Valley of Mexico has witnessed in the half millennium since Hernán Cortés and his troops first entered the Aztec capital of Tenochtitlán in 1519. Sited on a suite of islands amid the waters of Lake Texcoco, Tenochtitlán covered an area of some 13 square km, boasted numerous towering temple pyramids, and a population of 200,000. Today, vestiges of the fourteenth-century Aztec capital, including its Templo Mayor—dedicated to the gods of rain and war—lie beneath the Zócalo, or main plaza, at the very heart of Mexico City’s Historic Center, surmounted by some of the most splendid colonial architecture the New World has known. Some 680 square blocks constitute the Historic Center, within which are literally thousands of important buildings. The most prominent embrace the Zócalo, its northern end anchored by the imposing Metropolitan Cathedral. Built between 1573 and 1810, the cathedral is the largest church in Latin America. On the western edge of the Zócalo is the Palacio Nacional, erected on the site of Moctezuma II’s palace in the late seventeenth century. Within it is a poignant cycle of murals by Diego Rivera, among them the Epic of the Mexican People in their Struggle for Freedom and Independence, which depicts some 2,000 years of history. More recent treasures include the Palacio de Bellas Artes, an Art Nouveau wonder on the eastern side of Alameda Park, eight blocks west of the Zócalo.