September 21st or 22nd, 454, was the date on which the Roman general Flavius Aetius was assassinated, after the defeat of Attila and the Huns:
The most immediate effect of the collapse of the Huns was that the emperor Valentinian III, thirty-five years old in 454, felt no further need of Aetius. Aetius himself woul seem to have sensed this, since in that year he pressed the emperor into a marriage alliance. Aetius’ son Gaudentius was to marry Valentinian’s daughter Placidia. Since Valentinian had no son, this would have reinforced Aeitius’ political pre-eminence by making his son Valentinian’s likely successor. Valentinian, however, resented the move, and there were other western politicians wh ochafed under Aetius’ long-standing predominance, not least the senator Petronius Maximus who encouraged the emperor to act. Valentinian assassinated Aetius personally, we are told, on 21 or 22 September 454. Valentinian himself was murdered the next March by two of Aetius’ bodyguards. The disappearance from the scene of Aeitius, Valentinian and, above all, Attila marked the opening of a new (and final) era in the history of the Roman west. (Peter Heather in Cambridge Ancient History vol. 14 (2000), p. 18)