Federico Cantú 1907-1989
The coat of arms recalls the founding of Mexico City, then called Tenochtitlan. The legend of Tenochtitlan as shown in the original Mexica codices, paintings, and post-Cortesian codices, does not include a snake. While the Fejérváry-Mayer codex depicts an eagle attacking a snake, other Mexica illustrations, such as the Codex Mendoza, show only an eagle; in the text of the Ramírez Codex, however, Huitzilopochtli asked the Tenochtitlan people to look for an eagle devouring a snake, perched on an prickly pear cactus. In the text by Chimalpahin Cuauhtlehuanitzin, the eagle is devouring something, but it is not mentioned what it is. Still other versions (such as the backside of the Teocalli of the Sacred War) show the eagle clutching the Aztec symbol of war, the Atl-Tlachinolli glyph, or "burning water".

Moreover, the original meanings of the symbols were different in numerous aspects. The eagle was a representation of the sun god Huitzilopochtli, who was very important, as the Mexicas referred to themselves as the "People of the Sun". The cactus (Opuntia ficus-indica), full of its fruits, called "nochtli" in Nahuatl, represent the island of Tenochtitlan. To the Mexicas, the snake represented wisdom, and it had strong connotations with the god Quetzalcoatl. The story of the snake was derived from an incorrect translation of the Crónica mexicáyotl by Fernando Alvarado Tezozómoc.[citation needed] In the story, the Nahuatl text ihuan cohuatl izomocayan, "the snake hisses", was mistranslated as "the snake is torn". Based on this, Father Diego Durán reinterpreted the legend so that the eagle represents all that is good and right, while the snake represents evil and sin. Despite its inaccuracy, the new legend was adopted because it conformed with European heraldic tradition. To the Europeans it would represent the struggle between good and evil.