Templo Mayor was the ceremonial and spiritual core of Tenochtitlan, capital of the Mexica Empire — better known as the Aztecs. Now, centuries later, a new study reveals that it was also a node in one of the most sophisticated trade networks in pre-Columbian America.

The crux of this study is obsidian.

The Aztecs greatly cherished obsidian, a type of naturally occurring volcanic glass. They used it for everyday tools due to its sharpness, but also in ceremonial objects due to its symbolic value. In a paper published this week in Proceedings of the National Academy of Sciences, archaeologists report a sweeping analysis of 788 obsidian artifacts excavated from the Templo Mayor.

“This is the largest sample of obsidian artifacts ever analyzed for Tenochtitlan,” Diego Matadamas-Gomora, the study’s lead author and a PhD candidate at Tulane University, told us in an email. By studying where this material came from, we can explore the movement of goods across Mesoamerica.

A Geological Fingerprint

Obsidian isn’t just glass — it’s a geological time capsule. Obsidian is formed when a lava rich in silica cools extremely rapidly, without forming crystals. Each deposit carries a unique “chemical fingerprint” tied to the volcano that birthed it, explains Matadamas-Gomora. Using portable X-ray fluorescence (pXRF) scanners, researchers identified obsidian from at least eight different sources. Most came from Sierra de Pachuca, a volcanic range whose green-hued obsidian held symbolic weight for the Aztecs.

That green color mattered a lot.

“The Mexica called green obsidian ‘obsidian of the masters’ and considered it the most valuable,” said Matadamas-Gomora. Beyond its beauty, the green glass offered exceptional quality, ideal for crafting ritual objects like miniature weapons and jewelry found in sacred offerings. “Most obsidians are naturally gray or black. Green obsidian from Sierra de Pachuca is unique and related to this specific geological source. The Mexica recognized and valued that.”

Yet what surprised the researchers wasn’t just the obsidian from familiar sources but the sheer diversity of sources.

Overall, nearly 90% of the obsidian artifacts in the sample were made with the green obsidian. But obsidian also arrived from places like Otumba, Tulancingo, El Paraíso, and Ucareo — from all around, basically. And these weren’t spoils of war. These were gained through trade.

“I am surprised by the diversity of obsidian types we found at Tenochtitlan. However, my main surprise is that most of that variability is represented by non-ritual artifacts. This demonstrates that the state did not control access to obsidian tools.”

In other words, the Mexica didn’t just conquer their neighbors — they traded with them. Sometimes, even with rivals.

Tools for the People, Rituals for the Gods

Artifacts made from green obsidian were almost exclusively ceremonial. But the more mundane tools like arrowheads, blades, and scrapers were crafted from a range of obsidian types. These were found in construction fill and common areas, not elite offerings. That suggests that the average resident of Tenochtitlan had regular access to obsidian tools through markets. As the authors explain, it wasn’t state-managed.

This challenges another long-standing assumption: that the Mexica economy was dominated by tribute and conquest. The data tell a more nuanced story. Thriving markets also existed.

“It has been commonly assumed that the Mexica acquired most of its products through tribute payments,” said Matadamas-Gomora. “However, obsidian does not appear in the list of tributes.” That, he explained, suggests a hybrid system. Yes, there were state-run workshops producing ceremonial objects. But there was also a bustling commercial exchange, outside imperial control.

“On the one hand, the Mexica probably had a specialized group of miners and craftsmen who mined green obsidian and manufactured ritual objects and high-quality jewelry. At the same time, green obsidian objects and objects of various other obsidian types were produced outside of state control and distributed through the different markets.”

This distribution also seemed to change with time. In Tenochtitlan’s early years, around 1375 CE, the diversity of obsidian sources was relatively low. But after 1430 CE — when the Mexica began consolidating their empire — the number of sources increased sharply. That expansion paralleled the empire’s military victories and growth in political influence.

Obsidian As An Economic Lens

The study is a remarkable mix of archaeology, geology, chemistry, and economics. It’s striking that we can use chemical signatures to figure out various systems within ancient societies.

“This work not only highlights the Mexica Empire’s reach and complexity but also demonstrates how the archaeological sciences can be leveraged to study ancient objects and what they can tell us about past cultural practices,” said study co-author Jason Nesbitt, an associate professor in Tulane’s Anthropology Department.

Obsidian was central to Aztec life — not just for crafting sharp tools and sacred offerings, but as a reflection of political power and economic exchange. Its journey from distant volcanoes to the heart of Tenochtitlan reveals a civilization deeply connected by trade, guided by symbolism, and driven by innovation.

Ultimately, this research reframes how we understand the Aztecs — not just as a city of warriors and priests, but as a metropolis pulsing with trade, diversity, and technological sophistication.