This study is concerned with how the Postclassic Mexica people developed their unique perspective of history and environment in a dynamic cultural context. By focusing on the process of conceptualization of the Nahuatl word 'xihuitl', the author analyzes the way the Mexica expressed their cognition. Xihuitl covers a range of meanings: 'turquoise', 'grass', 'solar year', 'comet', 'preciousness', 'blue-green' and 'fire'. The correlations of the meanings of xihuitl can be explained from a structural point of view. However, structural analysis does not reveal the dynamic experiential processes that produced such correlations in the minds of the Mexica. In order to account for this dynamic aspect of the concept, the author employs a theory drawn from cognitive science. This theory argues that the meanings and representations of a concept are metaphoric extensions that derive from the central sense of the concept. Applying this theory, the author examines the metaphoric extension of each xihuitl representation from the central sense. The author also analyzes the four media of expression-linguistic, iconographic, material and ritual-in which representations of xihuitl occur. The representations of xihuitl in each medium embody a particular aspect of the concept. At the same time, the concept as a whole was affected by the Mexica conceptual system-the way the Mexica saw their world-rooted in the connections they believed existed between themselves and those who established earlier Central Mexican civilizations.