Forty kilometres northeast of Mexico City, the Avenue of the Dead runs two kilometres through the ruins of a city that was, at its peak around 450 CE, the sixth largest in the world — home to perhaps 125,000 people, with an influence that extended across Mesoamerica. The Aztecs who came after did not know who built it. They called it Teotihuacán — "the place where the gods were created" — and believed it was here that the sun and moon were born. They were right that it was sacred. They did not know who had made it sacred.
Teotihuacán was a planned city — laid out on a grid oriented 15.5 degrees east of north, aligned to the setting of the Pleiades on the western horizon on the day the sun passes directly overhead. The entire city plan expresses this astronomical orientation: the Avenue of the Dead, the pyramids, the residential compounds, the market areas — all conform to the grid, which in turn conforms to the sky.
The people who built Teotihuacán are one of archaeology's great mysteries. We do not know what they called themselves, what language they spoke, or where they came from. Teotihuacán had no writing system we have been able to read — some symbolic notation exists in murals, but no decodable script. The city's founders, rulers, and religious specialists are entirely unknown by name.
What we know from the material record is that they were sophisticated urban planners, skilled engineers, accomplished artists, and long-distance traders whose obsidian, pottery, and iconography reached every corner of Mesoamerica. The city's influence on subsequent Mesoamerican cultures — Maya, Zapotec, Toltec, Aztec — was enormous and long-lasting. Teotihuacán imagery appears in Maya art centuries after the city's collapse.
Around 550 CE the city was destroyed — not by conquest but apparently by internal revolt. The civic and religious buildings along the Avenue of the Dead were burned systematically, apparently by the inhabitants themselves. The elite residential compounds were targeted; ordinary apartment complexes were left intact. It was not the destruction of an enemy but the overthrow of a ruling class. After the burning, the population dispersed. The city was never again inhabited at scale.
Teotihuacán is the greatest mystery in the ancient Americas. We know what it was. We know what it did. We do not know, in any fundamental sense, who built it — or what they thought they were building.
— Esther Pasztory, Teotihuacan: An Experiment in LivingRecent discoveries: In 2015 archaeologists using remote sensing technology discovered a tunnel beneath the Temple of Quetzalcóatl filled with liquid mercury — possibly representing the underworld river — and thousands of ritual objects. In 2017 a further tunnel system was discovered beneath the Pyramid of the Moon. Both remain under active excavation. Teotihuacán continues to reveal itself.