Prehispanic societies were integrated by different means. No one can doubt that ritual was one of the main integrative mechanisms, because it "links generations, unites men from different descent groups, unites women from different families, [and] connects the living to their ancestors" (Marcus 1998:1). As Marcus puts it, ritual is important in creating public spaces and structures but is also visible in the domestic domain. In village societies, women played an important role in domestic ritual (Marcus 1998), but in urban societies other participants were added to domestic ritual not only to communicate with the ancestors but also to offer special ceremonies and goods to the gods in ways that were sometimes dictated by the state (Manzanilla 2002). One of the most outstanding urban developments of Classic Mesoamerica was Teotihuacan, a huge, planned, multiethnic metropolis in Central Mexico (Figures 0.1 and 0.2) (Millon 1973). The importance of religion in this city can be assessed in different scales: The state religion is evident in the huge plazas (squares) and temples in the city's center, in the processions of priests and other officers portrayed in the mural paintings, and in the representations of the deities (in sculpture, battlements, vases, mural paintings, etc.). There seem to have been barrio temples that integrated people of particular sectors of the city. And the last scale is the domestic realm, where altars and temples were set in ritual courtyards and where ceremonies for the ancestors and deities, as well as termination rituals, may be traced (Manzanilla 2002). Joyce Marcus (1998:11) distinguishes three components in ritual: The content (the subject matter), the locus of performance (specific places where ancient rites were performed), and the performers. To assess the locus of performance and the objects involved in domestic ritual as well as other activity areas in Classic period apartment compounds at Teotihuacan, Mexico, we designed an interdisciplinary strategy that took into consideration chemical traces of activities preserved in plastered floors, as well as paleobiological macroremains, microscopic evidence (e.g., chemical compounds, pollen, phytoliths), architectural and funerary data, and distributions of artifacts and debris on floors of the Oztoyahualco (15B: N6W3) compound (Figure 3.1) (Barba et al. 1987; Manzanilla 1988-1989, 1993, 1996; Manzanilla and Barba 1990). Here, we consider ritual ceremonies as individual or group acts of a symbolic nature, which are repeated according to a set of rules. The same ritual ceremony may include prayers, sermons, taboos, games, immolations, sacrifices, magic, or mythical representations (Cazeneuve 1972). Such repeated activities leave their mark on the archaeological record. Experience (Barba et al. 1997) has demonstrated that floors made with lime plaster preserve chemical residues, providing evidence that can reveal ancient human activities. The contaminating liquids (blood, sweat, food, etc.) that were repeatedly spilled on the floors during rituals allow us to chemically identify the areas where the activity took place and characterize the perishable materials used. It is important to mention that most of our chemical analyses in archaeological sites have been oriented toward the study of domestic activities. The interpretations in these cases have been based on ethnographic analogies and ethnoarchaeological experiments in which food production, storage, and consumption activity areas, as well as rest and high traffic areas, have been determined (Barba 1986; Barba and Ortiz 1992; Barba et al. 1995). A few examples of the use of this method for the study of ancient ritual follow. Research on ritual activities in archaeological sites was carried out on floors of the Satunsat building, at Oxkintok in Yucatán, Mexico, to study a non-domestic archaeological structure (Ortiz and Barba 1992). Its architecture and associated archaeological material revealed that this building was devoted to initiation rituals, star observation, and time measurement (Rivera and Ferrándiz 1989:72-75). Its floors were systematically sampled and chemical results revealed very low phosphate values, totally different from the concentrations usually found in the household, confirming it was a non-domestic building (Ortiz and Barba 1992:124). Absence of phosphate precisely under Burial 1 at Room 6-in contrast with previous experiences with chemical residues in shaft tombs, where we found chemical residues produced by body decay (Barba, Linares et al. 1991; Ortiz 1996)-confirmed the hypothesis that it was a secondary burial, with bones exhumed from another place and carefully positioned on top of the floor, generating an event different from the original use of the structure (Ortiz and Barba 1992:124). In 1987, a small ritual structure was excavated in downtown Mexico City. This structure was an Aztec altar used around a.d. 1440, during the first developmental stages of Tenochtitlan, the Aztec capital. Based on the results of the chemical analyses, it was concluded that this structure played a role in the installation ceremony rituals of the Moyotlan neighborhood, close to the Great Temple of Tenochtitlan, and was used for community rituals later in time. The altar, or momoztli, at the corner of Palma and Venustiano Carranza streets in downtown Mexico City must be considered a sanctuary in the core of a cluster of domestic units where people once carried out daily ceremonies. Based on descriptions of ritual festivities and analytical chemical results, Fernando Getino and Agustín Ortiz (1997:128) suggested that evidence for a termination ritual marking the end of the structure's use was recovered; specifically two human burials, sacrificed birds, and pottery were interred just after the large flood during Ahuízotl's reign. They were contaminated by organic materials, primarily copal resins and blood spilled after the bird sacrifice. In addition, it