The geopolitics of obsidian supply in Postclassic Tlaxcallan: A portable X-ray fluorescence study

The geopolitical relations of ancient states were often materialized through the flows of highly valued objects, but such relations also involved territorial strategies to secure access to natural resources and ensure the supply of bulk goods. Portable X-ray fluorescence (pXRF) of obsidian provides an excellent tool for investigating how the territoriality of ancient states shaped the circulation of such bulk commodities at a macro-regional scale. Here, we present the results of a pXRF study of obsidian artifacts from the Late Postclassic (AD 1350-1520) urban center of Tlaxcallan, Mexico. A recent survey and mapping project of Tlaxcallan provides the data to examine its obsidian supply. To assign sources to artifacts we applied pXRF to a sample of 45 artifacts from Tlaxcallan and 35 geological samples from sources of obsidian that we considered likely to have supplied Tlaxcallan. Contrary to expected patterns, our findings challenge the view that the Tlaxcalteca were embedded in economic networks centered in the Basin of Mexico and the Aztec Empire. Our results suggest that the population of Tlaxcallan procured obsidian from sources that fell outside of the major obsidian supply networks already documented in Mesoamerica. Thus, our findings support the idea that the territories of Mesoamerican polities influenced the supply of obsidian and that further studies of the geopolitics of bulk goods supply in ancient states are warranted.