We aren’t the first generation to be impressed by the pre-Columbian megalopolis of Teotihuacán, in central Mexico. The ruins seemed ancient even to the Aztecs, who encountered it centuries after it was abandoned. Awed, the Aztecs gave the site its name: Teotihuacán, or “the place where gods were created.”Even by modern standards, Teotihuacán was massive. By 500 C.E. it housed some 200,000 people across its eight square miles. But, as with other pre-Columbian cities, something about city living didn’t stick for its inhabitants: They appear to have abandoned the area by 750 C.E. The mighty city they built still stands just an hour’s drive from Mexico City, making it a must-see on any visit to the Mexican capital.Who founded Teotihuacán?We don’t know. Evidence of human settlement there dates to about 400 B.C.E., but its largest structures were completed as late as 300 C.E.We call the people who eventually inhabited and developed Teotihuacán Teotihuacanos, but we don’t know where they came from or even what language they spoke. The city’s growth was likely accelerated by the migration of Maya, Mixtec, and Zapotec peoples to the area. Historians believe other Teotihuacanos may have arrived as refugees from Cuicuilco, a city destroyed by volcanic eruption in the first century C.E.What makes Teotihuacán so distinctive?First is its sheer size. Because of Teotihuacán’s proximity to a valuable obsidian deposit, historians believe the city essentially held a regional monopoly on the prized material. That allowed Teotihuacán to become very wealthy very quickly, and Teotihuacanos spared no expense in building their glorious city. The Pyramid of the Sun is the tallest structure in the ruins at an astonishing 216 feet tall. The next tallest is the Pyramid of the Moon (140 feet), standing at the end of the Calle de los Muertos (“Avenue of the Dead”). The enormous road, 130 feet wide and 1.5 miles long, is lined with royal residences. In total, Teotihuacán’s ruins contain some 2,000 single-story apartment compounds.The Avenue of the Dead seen from the Pyramid of the Moon, Teotihuacán DeAgostini/Getty Images)De Agostini via Getty Images.Teotihuacán’s ruins are remarkably well organized. As a precursor to future American cities, Teotihuacán was clearly built on a grid. And the ruins are very well preserved: Visitors can even see traces of the vivid red hematite paint that once covered the Temple of Quetzalcóatl, which stands in the 38-acre Ciudadela (citadel).In 1989 archaeologists uncovered the bodies of what appeared to be sacrificial victims near the temple. It semes the sacrificed were killed around the time of the temple’s completion and were respected individuals: Many men were in military garb, while the bodies of others indicated their high social status. More evidence of human and animal sacrifices were uncovered near the Pyramid of the Moon in 2004.What was the Pyramid of the Sun used for?We don’t know for sure, but archaeologists unearthed a major clue in 2013: a pit at the pyramid’s summit. Within the pit, excavation teams uncovered the statue of a god easily identifiable as Huehueteotl, the Old God of Fire, in the Mesoamerican pantheon. The discovery appears to confirm researchers’ hunch that the pyramid was used as a temple or place of worship.A sculpture of Huehueteotl, the Old God of Fire, Museo de la Cultura Teotihuacana, TeotihuacánApolline Guillerot-Malick/SOPA Images/LightRocket via Getty Images.Why did people stop living at Teotihuacán?The ruins carry evidence of a catastrophic fire and targeted damage to monuments dating to the seventh century C.E. We don’t know their cause—historians suspect an internal conflict of some kind, like a coup, uprising, or civil war—but we do know that Teotihuacán’s population began to drop off dramatically thereafter.Teotihuacán was first excavated in 1884, followed by more comprehensive archaeological projects over the ensuing century. It became a UNESCO World Heritage site in 1987.