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Assassination

Although in 453 Aetius had been able to betroth his son Gaudentius to Valentinian's daughter Placidia, Valentinian felt intimidated by Aetius, who some 30 years prior had supported Joannes against him and who, Valentinian believed, wanted to place his son on the throne. The Roman senator Petronius Maximus and the chamberlain Heraclius were therefore able to enlist Valentinian in a plot to assassinate Aetius. The ancient historian Priscus of Panium reports that on 21 September 454, while Aetius was at court in Ravenna delivering a financial account, Valentinian suddenly leaped from his seat and declared that he would no longer be the victim of Aetius's drunken depravities. He held Aetius responsible for the empire's troubles and accused him of trying to steal the empire from him. When Aetius attempted to defend himself from the charges, Valentinian drew his sword and together with Heraclius, struck Aetius on the head, killing him instantly. Later, when Valentinian boasted that he had done well in disposing of Aetius, someone at court responded, "Whether well or not, I do not know. But know that you have cut off your right hand with your left." Edward Gibbon credits Sidonius Apollinaris with this famous observation.

Maximus expected to be made patrician in place of Aetius, but was blocked by Heraclius. Seeking revenge, Maximus arranged with two Huns who were friends of Aetius, Optila and Thraustila, to assassinate both Valentinian III and Heraclius. On 16 March 455, 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.