The archaeological site of Teotihuacan which is located in the Valley of Mexico a short distance from Mexico City was, at its apogee, one of the largest and most populous prehistoric metropolises in the New World. Construction at its sacred center was initiated during the first two centuries B.C. During the following stage of monumental construction a series of large imposing stone pyramids were erected; the urban area around them covered approximately 20 square km, with about 60,000 to 80,000 inhabitants by A.D. 150. The Teotihuacan state extended its influences throughout many parts of Mesoamerica and its power continued for centuries until its apparently sudden collapse in the seventh century. Although archaeologists most often focus their attention on large impressive structures associated with high ranking elites ,at Teotihuacan just the opposite is the case. Extensive survey and excavation over decades has resulted in the exposure of many typical house compounds and a great deal is known about `ordinary` life at the site. In a prior NSF supported project Dr. Sugiyama and his collaborators undertook important excavation at the Feathered Serpent Pyramid. Working both around and underneath this structure they recovered large numbers of sacrificial burials (apparently of prisoners) as well as graves of royal members of society. This has shed a preliminary light on one significant social stratum. With NSF support, this approach will be continued at the massive Moon Pyramid. Through excavation in the immediate vicinity as well as tunneling under the structure itself, the investigators will attempt to answer a number of questions. They wish to date the structure and determine the construction stages. They hope to recover, royal burials, sacrificial remains as well as other cultural materials. The Pyramids were designed to reflect the society's basic ideology and both the layout of burials and the materials they contain shed light on systems of belief, social organization and political control. Archaeologists wish to understand how complex societies arise and how, with simple technological systems, large numbers of people are organized into state systems. Mechanisms that establish and maintain hierarchies and which facilitate social control play a vital part in this process. This research will elucidate them at one of the most important sites in the New World.