The Praetorian Guard (cohors praetoria) was established in Rome as an elite squad of personal bodyguards of the Roman emperors. They accompanied the Emperor on all his campaigns. There are a number of factual reports regarding the involvement of the Praetorian Guard in the political system of Rome. In the Roman Empire, the ruler who controlled the army, the legions and more importantly, the Praetorian Guard had better control over his empire.
Roman emperor had to earn the respect of his subjects; and, at the same time, expect his commands to be obeyed. The Praetorian Guard acted as intermediaries between the emperor and the people. The Guard commanded a stature higher than the Roman legions and the auxiliaries. Their role was to maintain order in Rome. They also acted as the police force for the country of Italy. They were normally recruited from the city of Rome itself and not from its neighboring provinces -- unlike the legions and auxiliaries
Emperor Augustus Caesar started the Praetorian Guard in 367 B.C. following the murder of Julius Caesar (Winnat, date unknown). As the Guard was primarily responsible for the emperors' safety, the Emperor could induct into the Guard any person he saw fit for the position. It was also at the Emperor's discretion that any guard could be ousted as unfit. Members of the Praetorian Guard had a special uniform, received a double pay and also received bribes from the public and the elite, which were given to them in the guise of bonuses for their cooperation (RelicHunter Online, date unknown)
The Praetorian Guard consisted of nine cohorts of 500 men each (Roman Empire Online). A tribune, together with two equestrians, commanded a cohort. Praetorian Prefects, who were below senatorial rank, commanded the guard. The service time for the Praetorian Guard was sixteen years after which they were held back from discharge. Their service time was much shorter that that of the other type of warriors in the Roman Empire.
There was no effective system of selecting the Emperor in Rome as there was in the Greek Empire. The old Emperor, the Senate, the Praetorian Guard and the army selected the new Emperor. The Praetorian Guard gained complete authority in the Emperor's selection. The Emperor, in turn, rewarded the guards. This increased the influence and the power of the Praetorian Guard in the Roman Empire. The Guard became an instrument of political repression and an engine of political change.
They eventually started killing the emperor and then giving the throne of Rome to the highest bidder in the Empire (History Alive Online, date unknown). The Praetorians and the regular legions received bonus payments to celebrate the new emperor's accession to the throne. Servius Sulpicius Galba (3 BC - AD 69) who ruled between A.D. 68-69 stated, "I choose my soldiers; I do not buy them." He was however, one of the rare successors to the Roman throne who did not want to bribe the Praetorian Guard. The Praetorian Guard, in a conspiracy organized by Otho, assassinated Galba. He had reigned for only seven months.
Thus started the practice of selling the throne to the highest bidder -- the start of the downfall of the Roman Empire. In the next 100 years, Rome had 37 different emperors, 25 of whom were assassinated. Constantine in 312 A. D eventually closed down the Guard.
With the immense power, there was a lot of prestige associated with being a Praetorian guard. The applicants were generally from the Praetor caste although some noble families from the patrician houses also sent their sons and daughters to join the Guard. A panel chosen by the Pontifex interviewed the applicants. After selection, the recruits were sent off to 'The Nest.' It was located in the Western Empire where the recruits were trained (Empyreans Praetorians Online, date unknown).
The recruits, on completing their training and testing were then initiated into the Guard in a mysterious ceremony held at dusk on the summer and winter solstices, swearing to an oath, "I, (name of inductee), pledge my life, my honor, and my service to the Praetorian Guard. I pledge to uphold the laws of the Empire, and to defend her in all things. Let my ancestors witness this oath and all know that its violation shall be my…