In 275 BC, a troop of five hundred soldiers stood guard around General Scipio Aemilianus during the Siege of Numantia. These men were not yet an imperial institution but temporary escorts for high-ranking officials in the Roman Republic. Commanders with imperium held public office and were provided with lictors to protect their persons. When no permanent bodyguard existed, senior field officers like Scipio relied on selected soldiers from their legions. This practice continued through the late Republic as generals campaigned across Hispania Citerior and beyond. By 40 BC, Octavian and Mark Antony each maintained Praetorian Guards within their respective spheres of influence. Octavian installed his praetorians inside the pomerium, the sacred boundary of Rome, marking the first time troops were permanently garrisoned there. At Actium in 31 BC, Octavian commanded five cohorts while Antony led three more. After defeating Antony, Octavian merged these forces into a single unit numbering at most 5,400 men organized into nine cohorts. As Augustus became Rome's first emperor in 27 BC, he retained this force as his personal security escort.
Imperial Power And Politics
In AD 41, members of the Praetorian Guard discovered Claudius hiding behind a curtain after assassinating Caligula. They proclaimed him emperor because they needed an imperial figure to justify their own existence. Claudius compensated them with a bonus worth five years' salary. The Guard's political power grew under Sejanus, who became sole prefect in AD 15 and concentrated all cohorts under his command. He poisoned Drusus Julius Caesar in AD 19 and eliminated competitors until Tiberius ordered his execution in AD 31. In AD 68, Nymphidius Sabinus promised each Praetorian 7,500 denarii to abandon Nero for Galba. When Galba refused payment, Otho bribed twenty-three Speculatores to proclaim himself emperor instead. Galba and Piso were lynched on January 15th. During the Year of Four Emperors, Vitellius disbanded existing cohorts and established sixteen new ones totaling nearly 16,000 men. Vespasian later reduced the guard back to nine cohorts while appointing his son Titus as prefect. In 193, Didius Julianus purchased the empire from the Praetorians after they auctioned it off following Pertinax's assassination.