What happened to Teotihuacan

A city of possibly a hundred thousand people, one of the largest on earth, stopped. Not slowly, at the centre. The monumental buildings along the Avenue of the Dead were burned, and six hundred years later the Aztecs walked into an empty ruin and assumed gods had made it.

Here is what the evidence actually supports.

The burning was selective

This is the fact that shapes every explanation. Around the middle of the sixth century, structures along the ceremonial core were burned. The burning concentrated on elite residences and temples rather than spreading across the residential districts.

A foreign army sacking a city does not usually work that way. It takes what it wants and burns what is convenient. Targeting the ceremonial and elite architecture specifically, while ordinary apartment compounds survive, reads more like people who knew exactly which buildings represented the thing they were angry at.

That is the strongest single argument for internal collapse: revolt, factional conflict, or a rejection of the ruling institution by the city's own population.

What else was going on

Factor	What the evidence looks like
Selective burning of the ceremonial core	The clearest physical evidence, and it points inward rather than outward
Environmental stress	Central Mexico saw climatic pressure in this period, and a city of this size fed itself from a finite valley
Trade and obsidian	Teotihuacan's wealth rested on controlling obsidian distribution. Competitors emerging elsewhere would erode the basis of the whole thing
Population pressure	Tens of thousands of people in standardised compounds, dependent on a system that had to keep delivering
Foreign invasion	Possible, but the burning pattern argues against it as the primary cause

The honest summary is that these are not competing theories so much as a stack. A city under environmental and economic strain, whose ruling institution loses its claim on the population, is a city where somebody eventually burns the temples.

It did not empty overnight

Teotihuacan was not abandoned the morning after the fire. People continued living in parts of it for a long time afterwards, in reduced circumstances, without the monumental construction and without whatever central authority had organised the grid.

What ended was the city as a project: the planning, the building, the trade dominance, the reach that had let Teotihuacan install a ruler at Tikal in the fourth century. By around 750 CE the place was finished as a power.

Then it stood there, for six centuries, as an enormous ruin in a landscape that people still farmed and lived in.

What the Aztecs made of it

They arrived in the valley of Mexico much later and founded Tenochtitlan in 1325. By then the pyramids had been empty for longer than the gap between us and the Renaissance.

They had no memory of who built it, so they explained it theologically. The name they gave it, Teotihuacan, translates roughly as the place where the gods were created. They made pilgrimages, buried offerings, and named the buildings: the Avenue of the Dead, the Pyramid of the Sun, the Pyramid of the Moon. Every one of those names is Aztec, not original, which is the confusion at the heart of is Teotihuacan Aztec or Mayan.

What you can actually see of the collapse

Not much, honestly, and that is worth knowing before you go looking. The burning left archaeological traces rather than dramatic visible ruins, and the site has been consolidated and restored over more than a century of excavation.

What you can do is stand on the Avenue of the Dead knowing that the buildings on either side of you were deliberately set alight by people who lived here. That reframes the walk. The site museum, where the finds and the interpretation live, is where the story is actually told, and it is the part visitors on a compressed balloon-package schedule most often skip.

From the air the collapse is invisible, and what you get instead is the ambition: the full two-kilometre axis, the alignment of the Pyramid of the Moon with Cerro Gordo, the sheer completeness of the plan. Seeing how organised it was is what makes the ending land.

The part that stays with you

Teotihuacan is not a city that was conquered and remembered. It is a city whose own name is lost, whose rulers left no portraits, and whose people appear to have burned the heart of it themselves.

Then everyone forgot who they were, and the next civilisation to find the ruins decided only gods could have built them. Whatever makes a place worth flying over at sunrise, that is a strong candidate.