In a collaborative research project Dr. Thomas Charlton and Dr. Deborah Nichols will conduct archaeological research at the Aztec site of Otumba which is located in the Teotihuacan Valley, Mexico. One season of fieldwork will be followed by a year of analysis. The Otumba city-state includes a large central "city" area and smaller surrounding "rural" sites. The investigators will conduct a systematic surface survey and sampling of the city area to collect artifactual samples in order to understand how the site developed over time. They will then repeat the process at ca. three rural sites to determine the degree of economic interaction between them and the center. They will then conduct excavations at the center to learn how the city functioned economically and how it related to other similar city-states. Since the Aztec practiced irrigation agriculture, Drs. Charlton and Nichols will excavate the canal system to reconstruct its morphology, development and its importance for agricultural production. At the time Columbus discovered the New World, the Aztec had established a large, complex and centrally administered empire. While historical accounts provide some insight into how this empire functioned, archaeologists have argued about the processes which led to its development. This research should help to answer the question and provide more general insight into how complex societies arise.