Teotihuacan is an ancient Mesoamerican city located in a sub-valley of the Valley of Mexico, which is located in the State of Mexico, 40 kilometers northeast of modern-day Mexico City. Teotihuacan is known today as the site of many of the most architecturally significant Mesoamerican pyramids built in the pre-Columbian Americas. At its zenith, perhaps in the first half of the first millennium, Teotihuacan was the largest city in the pre-Columbian Americas, with a population estimated at 125,000 or more, making it at least the sixth-largest city in the world during its epoch.
The city covered eight square miles; 80 to 90 percent of the total population of the valley resided in Teotihuacan. Apart from the pyramids, Teotihuacan is also anthropologically significant for its complex, multi-family residential compounds, the Avenue of the Dead, and its vibrant, well-preserved murals. Additionally, Teotihuacan exported fine obsidian tools that are found throughout Mesoamerica. The city is thought to have been established around 100 BC, with major monuments continuously under construction until about 250 AD.