Calixtlahuaca, a Middle-Late Postclassic site in the Toluca Valley of central Mexico, was occupied ca. A.D. 1100-1530. Our excavations reveal some of the processes involved in the creation, functions, and decay of a large hilltop urban center. At its height, the majority of the site's surface (264 ha) was covered with residential-agricultural terraces supported by a complex water management system. House construction techniques included the use of adobe brick, wattle-and-daub, and stone pavements. Our fieldwork contributes to a growing body of research on hilltop political capitals in Mesoamerica. Using a refined chronology, we illuminate the processes by which people constructed the residential zones of this ancient hilltop city.