The arrest and punishment of members of the senatory elite was entrusted to the praetorians because their main duty was the protection of security of the emperor and his family and not that of the Urbs and its inhabitants. The protection of the Urbs was the task of soldiers, who were commanded by the most important of the senators of Rome, the urban prefect. The primary role was that of guarding the residence of the Princeps and to escort him personally in both public and official contexts. Cassius Dio, referring to ad 27 and explaining the etymology of the Palatium, talks about the residence of Augustus being near to his general quarters. In the picture that Suetonius draws in Chapter 49 of his Life of Augustus of the distribution of troops in the province, of the creation of the military fleets and of the urban troops, the civilian personnel responsible for the safeguarding of the person Princeps is understandably absent.