Teotihuacan is one of the most remarkable cities of the ancient world. It is known as the site of many of the most architecturally significant Mesoamerican pyramids built in the pre-Columbian Americas. At its zenith, Teotihuacan encompassed an urban core of about 20 square km with a population estimated at more than 100,000 people. At the time, it was one of the largest cities in the world and the region’s major economic and religious centre. The city was organized using a grid plan. Most impressive are two ancient pyramids, Pyramid of the Sun, the one of the largest structures of its type in the world, and Pyramid of the Moon. Both pyramids are connected by perfectly straight street called the Avenue of the Dead, which is lined with smaller pyramids.