The environmental characteristics of the upper Lerma river basin and the accessibility to the Balsas midelevation basin from its southern margins facilitated the settlement of different human groups since the early history of Mesoamerica. The mountain passes of Atlatlahuca were one of the most strategic ancient routes that communicated these basins, since no steep slopes had to be walked to descend or climb up over 700 meters, from the pre-Hispanic village of Atlatlahuca to the valley of Tenancingo. So far, the relevance of these mountain passes has not been recognized by the studies focused on the territorial evolution of the upper Lerma basin and neighboring regions.The fifteenth and sixteenth centuries were the time when the strategic quality of these mountain passes reached its peak, first under the rule of the Matlatzinca federation, and later by the Aztecs and their allies. Historical approaches to the territorial evolution of the upper Lerma basin have focused on the lacustrine area that used to cover the lowlands; in our view, this approach is insufficient to explain the territorial evolution of this basin. An approach beyond watersheds or contemporary administrative limits, encompassing broader temporal and spatial scales, has revealed the strategic character of these mountain passes. Understanding these territorial priorities also requires to acknowledge the changes in landscape of the main historical settlements that controlled the access to these mountain passes: Tenango and Atlatlahuca. Our goal is not to outline a definitive version of this territorial structure; instead, we want to set the grounds for a discussion from a geographical viewpoint ranging several historic stages.Our explanation is based on the principles of contemporary Cultural Geography and their application to areas of Mesoamerican tradition, and was derived from a continuous temporal analysis encompassing the Mesoamerican Post-Classic period and most of the 16th century. The cultural approach in geography aims to understand the thoughts and priorities of local inhabitants within their territorial context in different historical stages. In our case, the territorial structure we aim to explain involves physical changes in landscape, as well as changes in land use or in the way the environment is perceived according to different cultural practices.In physical and biological terms, our case of study is located in the transition zone between Nearctic and Neotropical regions in southern-central Mexico. The mountain passes of Atlatlahuca descend from around 2 700 m a.s.l. to approximately 2 000 m in the valley of Tenancingo within less than 15 kilometers. The physical characteristics that assured a broad range of supplies and the control of vast territories. In our cultural reconstruction, besides physical and biological conditions, it is also necessary to understand the concept of altepetl: a nahuatl word that literally means “water mountain” and defines the Mesoamerican post-Classic urban space. Most of the altepetl found by the Spaniards became pueblos de indios in the sixteenth century. In the Matlatzinca language –the predominant language in the area before the Aztec conquest circa 1470– altepetl translates to inpuhetzi.The territorial structure we attempt to explain is based on the settlement of several inpuhetzi during the early Mesoamerican post-Classic times, some at the Nevado de Toluca piedmont and others on isolated mountains within the upper Lerma basin: Tenango and Atlaltlahuca were among these settlements. This location allowed the Matlatzinca people to defend themselves from the attacks coming from the basin of Mexico. However, this defense does not explain the permanence and magnificence accomplished by the Matlatzinca for centuries. For us, the control of the Atlatlahuca mountain passes is key in the achievement of such grandeur, a territorial pattern shared with other nations settled along the Trans-Mexican Volcanic Belt. In this territorial logic, huge volcanoes or steep canyons were not territorial boundaries but articulation means. The importance of the Atlatlahuca mountain pass area also derives from the large number of political and administrative units settled there before the Spanish conquest. In less than 200 square kilometers there were six altepetl and two villages ruled directly from Tacuba, a minor partner of the Aztecs.The Spanish conquest led to the abandonment of this ancient route. First, its strategic value from a military point of view disappeared after the whole of central Mexico was under Spanish control. Second, the depopulation throughout the sixteenth century and the priority given by Spaniards to the healthy highlands led to the abandonment of most of the ancient commercial routes. Third, among the major mining towns located southwest of Mexico City, only Zacualpan continued using this route, which was also used by the wheat producers from the valley of Tenancingo and by merchants that traveled far into depopulated tropical lands. This commercial activity started to grow in the second half of the eighteenth century, when repopulation started and some tropical products were demanded by world markets.