The ancient civilization responsible for the construction of the monumental city of Teotihuacan in present-day Mexico is not definitively known, but it is believed to have been built by the Teotihuacanos, a pre-Columbian civilization that flourished from around 200 BCE to 650 CE. Teotihuacan was one of the largest and most influential cities in the ancient world, with impressive architecture and urban planning, including the Pyramid of the Sun, the Pyramid of the Moon, and the Avenue of the Dead. The city's influence is evident in the art, architecture, and religion of later Mesoamerican civilizations.