We have seen that the powers on which Augustus based his position as Princeps were the _proconsulare imperium_ and the _tribunicia potestas_. In the theory of a constitution which he presented to the world the first of these prerogatives was supposed to establish his power outside Rome and Italy, the second, with its purely civic traditions, to be the basis of his influence within the central state. His object in exalting the tribunician power to the first place in Rome and her Italian dependencies now merged in the city, was to conceal as carefully as possible the military basis of his rule. The unlimited _imperium_ was to be felt only by his army and his provincial subjects. It needed little reflection to show that this principle, although in appearance the most important that underlay the Principate, was practically unworkable. Government in Rome was inconceivable without an _imperium_, and supreme government impossible without one of such an indefinite character that it should seem to stand out of relation to the regular and limited _imperia_ of consuls and praetors. This power was secured by an easy juristic device. By a special exemption, which had its prototypes in Republican history, the Emperor was allowed to _retain_ the full _imperium_ within the walls;[1585] and lawyers were careful not to declare explicitly what was implied in this retention. It might have meant—as it would have meant during the Republic—that the Emperor was not debarred by his presence in Rome from holding command abroad. It might signify that the limitations imposed by the city walls now rendered the proconsular a quasi-consular _imperium_, and this was perhaps the ruling theory. But a different line of interpretation would have rendered it easy to show that the _imperium_ here as elsewhere was unlimited. The nebulous atmosphere of this mockery of a magistracy was as well suited to the despot as to the constitutional ruler. In the actual position of the Princeps within Rome we find traces of all these theories. As a provincial ruler he governs from the capital; as commander-in-chief he keeps his praetorian guards in Italy and his fleets at Ravenna and Misenum; while as the wielder of an undefined but civic _imperium_ he gives justice, as a court of first instance or a court of appeal, and issues edicts to supplement the laws.