I examine the problems and potentials of correlating diachronic archaeological and ethnohistorical data through the case of the Aztec (Triple Alliance) conquest of western Morelos, Mexico. To date, nearly all of our knowledge of the Triple Alliance empire is derived from ethnohistorical sources with little contribution from archaeological data. Two methodological problems account for this disparity. First, current archaeological chronologies for Postclassic central Mexico are not precise enough to document the structure and growth of this relatively short-lived empire. Second, the issue of diachronic correlation of archaeological data with the native historical record has not been approached with a consistent methodology. I address these problems, demonstrating that Postclassic chronologies can be refined when the appropriate methods (in this case, nontypological ceramic analysis and quantitative seriation) are applied. The resulting chronological sequence for western Morelos is correlated with the diachronic native historical record for the area. Because of these procedures, the archaeological record can for the first time make a significant contribution to the study of the Triple Alliance empire.