Located 50km (31 miles) northeast of Mexico City, Teotihuacán grew to be the largest of Mexico's pre-Hispanic cities, with an estimated population of 200,000 during its prime in the sixth century AD. Its greatest building is the Pyramid of the Sun, standing at a height of 63m (207ft). It is joined on the Avenue of the Dead, Teotihuacán's main street, by another enormous building, the Moon Pyramid, which was originally part of a 'Moon Plaza'. The site was first excavated in 1884. Visitors can also see the various palaces once inhabited by the priests who ruled the city; research has brought to light many of the rituals of this ancient civilisation, including ceremonial human sacrifice and elaborate festivals.