March 16 marks the anniversary of the assassination of the Western Roman Emperor Valentinian III in AD 455. Though he reigned for thirty years, Valentinian III presided over the slow but steady dismemberment of the Western Empire and was considered a weak and vacillating emperor. He had risen to the throne at the age of six or seven and was therefore under the thumb of powerful figures at court for most of his reign. Fortunately for him, one of these figures was the capable general Aetius who successfully defended the empire from the potentially cataclysmic invasion of Attila and his...