The quintessential day trip from Mexico City is a visit to Mexico's most popular archaelogical site, Teotihuacan. This ancient city was established somewhere around 100 BC and most of the construction lasted into 250 AD. By 400 AD, it was the largest city in the pre-columbian americas, with a population of about 125,000. Despite its grandeur, not much is known about the people who lived here (it’s neither Mayan nor Aztec).
The city’s downfall came in the 7th and 8th centuries, when much of it was ransacked and burned. It’s thought to have occurred as a result of internal unrest, catalyzed by droughts and widespread malnutrition.
The temple of the sun, the largest structure at the site, can be seen on the left in the photo above.