Teotihuacan is an ancient Mesoamerican city located in present-day Mexico. It flourished between 100 and 750 CE and is known for its impressive architecture, including the Pyramid of the Sun and the Pyramid of the Moon. At its peak, Teotihuacan was one of the largest cities in the world, with a population of over 100,000 people. The city was a major cultural and economic center, influencing many surrounding regions. Its layout features a grid pattern, with the Avenue of the Dead as the main thoroughfare. Teotihuacan's decline began around the 7th century, but its ruins continue to be a significant archaeological site today.