The Aztecs founded their city of Tenochtitlan (present-day Mexico City) on an island in Lake Texcoco in 1325 C.E. Other city-states remained uneasy with their presence and fighting continued. Finally, in 1430, the Aztecs formed an alliance with two other major settlements and it was then that the Aztec Empire was born. The empire flourished until Cortés arrived in 1521, who overthrew the Aztec Empire.