Shedding light on ancient trade: X-ray clues

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  • Published: Apr 1, 2015
  • Author: David Bradley
  • Channels: X-ray Spectrometry
thumbnail image: Shedding light on ancient trade: X-ray clues


The geopolitics of obsidian supply in Postclassic Tlaxcallan: A portable X-ray fluorescence study (Adapted public domain image)

X-ray fluorescence spectroscopy has been used to reveal the complexity of geopolitics in Mesoamerica during the Aztec era and to show how relationships between ancient states did not revolve only around warfare and diplomacy but were extended to issues concerning trade and the flow of goods.

Unearthing the geopolitics of ancient civilisations is always likely to be hard road to travel, but an international team of archaeological researchers has used modern analytical techniques to help them reveal the political boundaries and economic networks of the Aztec era of Mesoamerica. Scientists from North Carolina State University, the Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional-Unidad Mérida, El Colegio de Michoacán and Purdue University, Indiana focused on the independent republic of Tlaxcallan in what is modern-day central Mexico about 120 kilometres east of Mexico City. The founding of Tlaxcallan was in the mid-13th century but by 1500 the republic was effectively encircled by the Aztec Empire, although it never lost its independence. Indeed, Tlaxcallan supported Spanish Conquistador Hernán Cortés de Monroy y Pizarro and the republic played a critical role in the Spanish Conquest of Mexico in the 16th century.

Not so obvious obsidian

NC State's John Millhauser and colleagues have focused on the source of the obsidian used by the people of Tlaxcallan during the century before the arrival of Cortés. Obsidian is a volcanic glass comprising mainly silica but containing magnesium oxide and iron oxide. It was used widely in jewellery, household tools and weapons as well as ceremonial and religious objects. However, Tlaxcallan did not have its own endogenous supply of obsidian within its territory so must have sourced this material from elsewhere.

"It turns out that Tlaxcallan relied on a source we hadn't expected, called El Paredón," explains anthropologist Millhauser."Almost no one else was using El Paredón at the time, and it fell just outside the boundaries of the Aztec Empire. So, one question it raises is why the Aztecs - who were openly hostile to Tlaxcallan - didn't intervene."

It might be that the Aztecs didn't interfere with the obsidian supply simply because it would have been too much effort. Obsidian was widely available and considered part of everyday goods. "It probably wasn't worth the time and expense to try to cut off Tlaxcallan's supply of obsidian from El Paredón because other sources were available," Millhauser says. This suggestion emphasises once again how complex international relations were during the predominance of the Aztec Empire in this region.

"The fact that they got so much obsidian so close to the Aztec Empire makes me question the scope of conflict at the time," Millhauser adds. "Tlaxcallan was able to access a source of household and military goods from a source that required it to go right up to the border of enemy territory."

Economic rift

The team does point out that, nevertheless, there was an economic rift between Tlaxcallan and the Aztec Empires. Earlier research had shown that more than 90 percent of Aztec obsidian had come from the Pachuca source, further to the north. Aztec commercial networks distributed Pachuca obsidian far and wide, but the new research finds that only 14 percent of the obsidian at Tlaxcallan was from Pachuca. The majority of the remainder was from El Paredón. For this work, the team had systematically collected artefacts from the surfaces of stone-walled terraces at Tlaxcallan and analysed a representative number with X-ray fluorescence. This information was compared with samples from other known sources to locate their origin.

"Political stances and political boundaries influenced everyday behaviour, down to the flow of basic commodities like obsidian," Millhauser adds. "The popular conception of the Aztec Empire as all powerful before the arrival of Cortés is exaggerated. The Aztec and their enemies acted strategically to secure their interests, and they did so in ways that we are still coming to know," Millhauser told SpectroscopyNOW.

Related Links

J Archaeol Sci 2015, 1-14: "The geopolitics of obsidian supply in Postclassic Tlaxcallan: A portable X-ray fluorescence study"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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