That would be Teotihuacan, located just northeast of where Mexico City is today in a sub-valley of the Valley of Mexico. At its height, Teotihuacan had a population of between 100,000 and 200,000 people. It's ceremonial core, which is what you mostly see today in the partially restored and open tourist area of the city, covers about 26 km2. Throughout the city's life different neighborhoods and regions were occupied at different times and for whatever reason were abandoned and then reoccupied. Surveys in the 60s by Rene Millon and his team had found that the total area the city covered was 53 km2, with the outer edges of the city consisting of households spaced further apart in order to farm or grow gardens.

Despite it's Nahuatl sounding name, we don't actually know what the city was called, what the people that occupied the city called themselves, or even what language they might have spoken. The name of the city was bestowed upon Nahuatl speakers who came across the ruins hundreds of the years after the city's abandonment. The name itself is translated as "the place where gods were born", but whether this had to do with the impressive size of the pyramids of the Sun and Moon, whether this has anything to do with Aztec belief, or something else is uncertain.

Teotihuacan seemed to have meddled in Maya affairs in the 300s going so far as what some might think is an invasion. The ruler of Tikal, a very powerful city-state in the Maya region, had its ruler deposed with someone who had strong ties to Teotihuacan put in their place. While this is an information blackout period at Tikal with little in the way of writing about the events, other sites have documented this entrada. What's curious about this entrada is that Maya artists depict these foreigners not in their own Maya artistic portrayal of people, but in the way Teotihuacan depicts its people. So see monuments with two different art styles along with iconographic elements not previously found in Maya artwork. The emphasis on these foreigners using atlatls is interesting because atlatls were not necessarily the weapon of choice among the Maya, but were the weapon of choice among Teotihuacanos. Within those monuments the Maya had said that these foreigners came from a placed called Pu, which in Maya means "place of many reeds". However, in Mesoamerica a place of many reeds simply meant a city with many people. In Nahuatl the term is Tollan which you may have heard. Many of the cities in Central Mexico had Tollan attached to their name like Tula Tollan for the Toltecs or Cholula Tollan in Puebla. While the name Pu may not have been the Mayanized name for Teotihuacan, it is interesting to know that the association of densely populated cities with a place of many reeds stretches that far back in Mesoamerican history.