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The Praetorian Guards were usually the only significant military unit in Rome if not Italy. There was an urban militia (vigiles), and the German bodyguard of the Emperor, however, the Guards were by far the most formidable military force in the capital. This and their unique access to the Emperor meant that they were in a position to intervene in Imperial affairs. The Emperor came to depend on the Guard for his safety and over time the Imperial bodyguard began to become ‘conscious of their power’ power.’<ref>Bingham, p 167</ref>. The ruler of the Roman World was at their mercy if they acted in unison and decisively. They Guards were instrumental in the deposition of countless Emperors the exact number is unknown.

The Praetorians because of their proximity to the absolute ruler of the known world knew that his power was depended on deference and the unthinking obedience of the population. The Imperial Bodyguard, under Prefects such as Sejanus, recognized that ultimately power depended on brute force and that they had a monopoly on violence in Rome. As a result, the Imperial Guard played a huge role in the history of the Empire. They had the ability, which the Senate did not have of making and unmaking the absolute ruler of the Roman world. It should be remembered that the guards could only depose Emperors who were weak or during times of crisis. For the majority of their existence, strong rulers controlled the elite bodyguard. There are long periods in the 2nd century, for example, when the bodyguard is not mentioned in the sources, because they were tightly controlled by rulers, such as Hadrian .<ref>Bingham, p 178</ref>.