The issue on the location of urban barracks and of the headquarters of the prefecture is, however, of particular importance, and in recent years has received adequate attention. The dangerous places that will be considered are enclosed public places. As in the Republican era, also in imperial times the security of the aristocratic residences remained a private matter. The topography of the barracks and of the guard posts of the vigiles in the fabric of Rome were gradually defined, with subsequent interventions during the first two centuries of the Imperial age, which can only be partly reconstructed. Robert Sablayrolles who has dedicated a reference monograph to the libertini milites in 1996, does not rule out that the construction plan of the barracks of the vigiles dates back to the Augustan age. Sablayrolles is the one to offer the most comprehensive and debated review on the structures identified and divided into sure, probable and still unknown.