The Aztecs began as an migrating tribe, the Nahua-speaking people in the 6th century. They migrated down from northern Mexico to Mesoamerica. They were the nomadic hunters, later on creating the diverse culture and practices of the future Aztecs. They later rose in strength in the Post-classic period, dominating sites such as Tuala, Hidalgo. It was at that time around 1100 when the Aztec Empire was beginning to get more and more populated by a group that was once nomadic, the Mexicas.
The true origin of the Mexicas is still unknown. Legends say that the Mexicas came from Aztlan. Experts believe that Aztlan is located somewhere north of the valley of Mexico. They were expelled to barren plains, and in 1325, they returned. Aztec legend says that the Mexicas were shown a vision, a eagle on a prickly cactus, showing where they should build their home. The Mexicas arrived on an island in Lake Texcoco, where they founded the the city of Tenochitlan in 1325. In 1376, they elected their first Huey Tlatoani, Acamapichtli. This was the pillar of the Triple Alliance, which rose and fell.