Teotihuacan

19.6925°N, 98.8439°W.

Pre-Columbian city in the Basin of Mexico, 40 km northeast of modern Mexico City. At its peak around 450 CE, Teotihuacan had a population of approximately 125,000 and covered 21 km², making it one of the six largest cities in the world at the time. The Pyramid of the Sun, base 222 by 225 metres and 65 metres tall, is the third-largest pyramid on Earth by volume; the Pyramid of the Moon at the north end of the Avenue of the Dead is precisely aligned to the sacred peak Cerro Gordo behind it. The city's central avenue is oriented 15.5° east of true north, an alignment that frames the Pleiades' heliacal rising at the latitude.

The collapse of Teotihuacan around 550 CE remains unexplained; the central ceremonial structures were burned and abandoned by their own population.