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 (25 mi) 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, namely Pyramid of the Sun and Pyramid of the Moon. At its zenith, perhaps in the first half of the first millennium (1 CE to 500 CE), Teotihuacan was the largest city in the Americas, considered as the first advanced civilization on the North American continent, 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 (21 km2), and 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 found throughout Mesoamerica. The city is thought to have been established around 100 BCE, with major monuments continuously under construction until about 250 CE. The city may have lasted until sometime between the 7th and 8th centuries CE, but its major monuments were sacked and systematically burned around 550 CE. Its collapse might be related to the extreme weather events of 535–536.

Teotihuacan began as a religious center in the Mexican Highlands around the first century CE. It became the largest and most populated center in the pre-Columbian Americas. Teotihuacan was home to multi-floor apartment compounds built to accommodate the large population. The term Teotihuacan (or Teotihuacano) is also used to refer to the whole civilization and cultural complex associated with the site.

Although it is a subject of debate whether Teotihuacan was the center of a state empire, its influence throughout Mesoamerica is well documented. Evidence of Teotihuacano presence is found at numerous sites in Veracruz and the Maya region. The later Aztecs saw these magnificent ruins and claimed a common ancestry with the Teotihuacanos, modifying and adopting aspects of their culture. The ethnicity of the inhabitants of Teotihuacan is the subject of debate. Possible candidates are the Nahua, Otomi, or Totonac ethnic groups. Other scholars have suggested that Teotihuacan was multi-ethnic, due to the discovery of cultural aspects connected to the Maya as well as Oto-Pamean people. It is clear that many different cultural groups lived in Teotihuacan during the height of its power, with migrants coming from all over, but especially from Oaxaca and the Gulf Coast.After the collapse of Teotihuacan, central Mexico was dominated by more regional powers, notably Xochicalco and Tula.