Today is the day the Triple Alliance died.
In 1521, the last tlatoani of Tenochtitlan, Cuauhtémoc, fought to defend the city from the Spanish conquistadores, and ended up having to flee because the city — after having pissed off the surrounding countryside for years — had almost no friends left except their allied city of Tlatelolco, so they got trounced. (Texcoco, the other city of the alliance, had been defeated and occupied by Cortés by this point; they used warriors from Texcoco in the final siege of Tenochtitlan, just to add insult to injury.) The fact that the city had been ravaged by smallpox didn’t help, and the fact Cuauhtémoc and his family were captured by the Spanish as they tried to escape put the nail in the coffin.
He wasn’t killed right away — in fact, Cortés essentially kept him around as a royal hostage for a few years — but in 1525, he claimed to have heard that Cuauhtémoc was plotting against him (with who and how, no one knows, and it’s very likely Cortés was full of shit), so he tortured him, and killed him, on February 28th.
According to Bernal Diaz de Castillo, his final words (through Malintzin interpreting them) were: Oh Malinzin [i.e., Cortés]! Now I understand your false promises and the kind of death you have had in store for me. For you are killing me unjustly. May God demand justice from you, as it was taken from me when I entrusted myself to you in my city of Mexico!