The term Praetorian derived from the tent of the commanding general or praetor of a Roman army in the field—the praetorium. They were an elite recruitment of Italians (Roman citizens and Latins). The emperors also often employed a small separate unit of bodyguards, distinct from and, in a degree, as a counterbalance to the Praetorian Guard 1. It was a habit of many Roman generals to choose from the ranks a private force of soldiers to act as guards of the tent or the person. They consisted of both infantry and cavalry. In time, this cohort came to be known as the cohors praetoria, and various notable figures possessed one, including Julius Caesar, Mark Antony and Augustus (Octavian). As Caesar discovered with the Legio X Equestris, a powerful unit more dangerous than its fellow legions was desirable in the field. When Augustus became the first ruler of the Roman Empire in 27 BC, he decided such a formation was useful not only on the battlefield but in politics also. Thus, from the ranks of the legions throughout the provinces, Augustus recruited the Praetorian Guard.
Original form of the Guard
The group that was formed initially differed greatly from the later Guard, which came to be a vital force in the power politics of Rome. While Augustus understood the need to have a protector in the maelstrom of Rome, he was careful to uphold the Republican veneer of his regime. Thus he allowed only nine cohorts to be formed, originally of 500, then increased to 1,000 men each, and only three were kept on duty at any given time in the capital. A small number of detached cavalry units (turmae, sing. turma) of 30 men each were also organized. While they patrolled inconspicuously in the palace and major buildings, the others were stationed in the towns surrounding Rome; no threats were possible from these individual cohorts. This system was not radically changed with the appointment by Augustus in 2 BC of two Praetorian prefects, Quintus Ostorius Scapula and Publius Salvius Aper, although organization and command were improved.
Through the machinations of their ambitious prefect, Lucius Aelius Sejanus, the Guard was brought from the Italian barracks into Rome itself. In 23, Sejanus convinced Tiberius to have the Castra Praetoria (the fort of the Praetorians) built just outside of Rome. One of these cohorts held the daily guard at the imperial palace switching roles in between patrols (most of the guard in the imperial palace had shifted roles from morning till evening). Henceforth the entire Guard was at the disposal of the emperors, but the rulers were now equally at the mercy of the Praetorians. The reality of this was seen in 31 when Tiberius was forced to rely upon his own cohors praetoria against partisans of Sejanus. Although the Praetorian Guard proved faithful to the aging Tiberius, their potential political power had been made clear.
Participation in wars
While campaigning, the Praetorians were the equal of any formation in the Roman Army. On the death of Augustus in 14 his successor Tiberius was faced with mutinies among both the Rhine and Pannonian legions. According to Tacitus, the Pannonian forces were dealt with by Tiberius’ son Drusus, accompanied by two Praetorian cohorts, the Praetorian cavalry and some of the German bodyguard. The German mutiny was put down by Tiberius’ stepson Germanicus, his intended heir, who then led the legions and detachments of the Guard in an invasion of Germany over the next two years. The Guard saw much action in 69, fighting well for Otho at the first battle of Bedriacum. Under Domitian and Trajan, the guard took part in wars from Dacia to Mesopotamia, while with Marcus Aurelius, years were spent on the Danubian frontier. Throughout the 3rd century, the Praetorians assisted the emperors in various campaigns.
Following the death of Sejanus, who was sacrificed for the Donativum (imperial gift) promised by Tiberius, the Guards began to play an increasingly ambitious and bloody game in the Empire. With the right amount of money, or at will, they assassinated emperors, bullied their own prefects, or turned on the people of Rome. In 41 Caligula was killed by conspirators from the senatorial class and from the Guard. The Praetorians placed Claudius on the throne, daring the Senate to oppose their decision.