But the recognition of an _imperium_ within Rome was not alone sufficient. Even when this was joined to the tribunician power, great gaps were left in the position which should be held by a true head of the state. To fill these up, and thus supply a solid foundation for autocracy, fresh grants of isolated powers were necessary; and these grants, though in theory occasional, soon became permanent in practice. The Emperor, like the tribune, possessed no distinctive official dress while he resided in Rome: hence the consular _insignia_ had to be conferred;[1586] he possessed in virtue of his tribunician power only the right of making the third proposal at the Senate: hence the grant of the _jus primae relationis_.[1587] Such grants admitted of indefinite extension, and the stage which they had reached by the date of the accession of Vespasian is partially known to us from the only official document which throws light on the powers of the early Principate. In the existing fragment of this charter, which appears to be a decree of the Senate meant to be submitted to the people for their formal assent,[1588] we find the Emperor credited with the heterogeneous powers of making treaties, extending the _pomerium_, commending candidates for magistracies, and issuing edicts as interpretations of law human and divine. The measure further exempts him from the operation of certain enactments and gives him certain privileges, not possessed by the other magistrates, in his relations with the Senate. These powers cannot be brought under any single legal designation; but, as most of them are more or less directly connected with some kind of _imperium_, the view that they were tacked on to the bill conferring the tribunician power, which received the formal ratification of the Plebs, is improbable. On the other hand, they cannot be said to have belonged originally to a law conferring the _imperium_; for the imperial biographies frequently speak of the gift of the _proconsulare imperium_ (by the Senate) and of the _tribunicia potestas_ (by Senate and People) without any hint of a general law conferring _the_ “imperium.”[1589] Yet the gift of the _imperium_ is sometimes mentioned,[1590] and if the passages of jurists of the second and third centuries, which speak of _imperium_ being conferred through a _lex_,[1591] are genuine, we must conclude that the centre of gravity in the powers of the Princeps had shifted with the course of years. Originally the casual collection of powers, which appears in the law sanctioning Vespasian’s rule, must have been a mere supplement to the two leading prerogatives—the proconsular and the tribunician powers. But it is quite possible that in the course of time the vast development and the great importance of these added privileges may have caused the enactment containing them, now known as the _lex de imperio_, to overshadow the other sources of the imperial authority.