High Quality Content by WIKIPEDIA articles! The city now known as Mexico City was founded by the Mexica, also called the Aztecs, in 1325. The old Mexica city is now referred to as Tenochtitlan. The Mexica were one of the last of the Nahuatl-speaking peoples who migrated to this part of the Valley of Mexico after the fall of the Toltec Empire. Their presence was resisted by the peoples who were already in the valley, but the Mexica were able to establish a city on a small island on the western side of Lake Texcoco. The Mexica themselves had a story about how their city was founded after being led to the island by their principal god, Huitzilopochtli. According to the story, the god indicated their new home with a sign, an eagle perched on a nopal cactus with a snake in its beak. Between 1325 and 1521, Tenochtitlan grew in size and strength, eventually dominating the other city-states around Lake Texcoco, and in the Valley of Mexico. When the Spaniards arrived, the Aztec Empire reached much of Mesoamerica, touching both the Gulf of Mexico and the Pacific Ocean.