About an hour bus ride north of Mexico City (the traffic is pretty rough) are the ruins of the ancient city of Teotihuacán. The centerpiece of the site is a promenade, the Avenue of the Dead, which stretches for two kilometers from the stepped temples of the ciudadela, across a small river, past the massive Pyramid of the Sun, among numerous ruins and smaller pyramids to the foot of the Pyramid of the Moon. All told, the site is nearly 78 square kilometers, and the names suggest that it’s most readily remembered as an Aztec ruin (because that’s who was here when the Spanish showed up), but the pyramids and avenues of Teotihuacán are much older than the Aztecs. In fact, what happened when the Aztecs found these pyramids is one of the most interesting and thought provoking parts of Teotihuacán’s history.

Originally constructed in the first century CE, the pyramids you can visit today were the centerpieces of a massive city of a forgotten civilization. Archaeologists estimate that this city was home to upwards of 125,000 people at its height, which would make it one of the 10 biggest cities in the world, at the time. But still, very little is known about the people who built these structures. When the Aztecs came by over a thousand years later, they certainly had no idea, and so they invented a story to explain what they found. Teotihuacán, they decided, was where their gods created the universe, and thus the site of their own origins.

But the question of origins is more complicated than that. Today archaeologists dig around the complex looking for clues, and though we have a better idea of the dates of construction, we know little more than the Aztecs about the builders. Instead of assigning our gods to their monuments, we seek to re-create theirs. Instead of naming the roads and areas for our cosmology, we name them for the uses we have assumed from the ruins. Still, despite our different approaches, just like the Aztecs, we are looking for our origins in Teotihuacán.

Humanity is actually pretty obsessed with where it came from. We’re certain that we’re remarkable. After all, humanity is pretty unrivaled on the planet, and so we’re convinced that there must be something important in our past. Our development, we reason, must be not only unique, but also powerful if we were to grow into the force in the world we see today. So we scour ruins across the globe, we infer purposes in their structures, we sketch beliefs from their artifacts. It’s not so much important to us who these people were, but we’re driven to understand what about them enabled the slow upward progress that resulted in us. The universe may not have been created at Teotihuacán, but a piece of humanity was, and that means it’s important.