Although in 453 Aëtius had been able to betroth his son Gaudentius to Valentinian's daughter Placidia, Valentinian felt intimidated by Aetius, who had once supported Joannes against him and whom Valentinian believed wanted to place his son upon the imperial throne. The Roman senator [[Petronius Maximus]] and the chamberlain Heraclius were therefore able to enlist Valentinian in a plot to assassinate Aëtius. On [[September 21]], [], when at court in [[Ravenna]] delivering a financial account, Aëtius was slain by Valentinian's own hand. [[Edward Gibbon]] credits [[Sidonius Apollinaris]] with the famous observation, "I am ignorant, sir, of your motives or provocations; I only know that you have acted like a man who has cut off his right hand with his left" (''Decline and Fall of the Roman Empire'', ch. 35).
Maximus expected to be made patrician in place of Aëtius, but was blocked by Heraclius. Seeking revenge, Maximus arranged with two Hun friends of Aëtius, Optila and Thraustila, to assassinate both Valentinian III and Heraclius. On [[ March 16]] , [], Optila stabbed the emperor in the temple as he dismounted in the Campus Martius and prepared for a session of archery practice. As the stunned emperor turned to see who had struck him, Optila finished him off with another thrust of his blade. Meanwhile, Thraustila stepped forward and killed Heraclius. Most of the soldiers standing close by had been faithful followers of Aetius and none lifted a hand to save the emperor.