A personal insult to Cassius Chaerea, tribune of a praetorian cohort, led to Caligula's assassination on the 24th of January 41.
Arrius Aper, praefect of the praetorian guards, his father-in-law, who was suspected of having murdered him, was slain by Diocletian, whom the soldiers had already proclaimed his successor.
In the second century the praetorian cohorts became ten in number, and at the end of it Septimius Severus reorganized them so that they consisted practically of barbarian soldiers and held constant conflict with the people of Rome.
Britannicus's leading partisans were banished or put to death, and the allimportant command of the praetorian guard was transferred to Afranius Burrus, a Gaul by birth, who had been the trusted agent first of Livia and then of Tiberius and Claudius.
His death was variously attributed to disease, the effects of lightning, or a wound received in a campaign against the Huns; but it seems more probable that he was murdered by the soldiers, who were averse from further campaigns against Persia, at the instigation of Arrius Aper, prefect of the praetorian guard.
During his minority the empire was ably ruled by the praetorian prefect Anthemius and Pulcheria, who became her brother's guardian in 414.
One of his first acts, after preventing the application of capital punishment to the ringleaders of the revolt, was to veto the project of protecting the khedive and his government by means of a Praetorian guard recruited from Asia Minor, Epirus, Austria and Switzerland, and to insist on the principle that Egypt must be governed in a truly liberal spirit.
Their place was filled by Poppaea, and the infamous Tigellinus, whose sympathy with Nero's sensual tastes had gained him the command of the praetorian guards in succession to Burrus.
This implied the continuance of praetorian methods of administration.
Otho had owed his success, not only to the resentment felt by the praetorian guards at Galba's well-meant attempts to curtail their privileges in the interests of discipline, but also largely to the attachment felt in Rome for the memory of Nero; and his first acts as emperor showed that he was not unmindful of the fact.