The Principate was, in the theory of the constitution, an elective office, and one based on the principle of occasional delegation. It was necessary for the life of the state that there should be a magistracy,[1674] but it was not necessary that there should be a Princeps. Hence there was no institution such as the Republican _interregnum_ to fill up the gap left by the vacancy of the throne,[1675] and the fact that such gaps did occur in the history of the Principate shows that the possibility of government by magistrates, senate, and people was no mere fiction. The abstract idea of a Principate was indeed perfectly realised at the death of the very first Princeps, in so far as responsible men in the Roman world had a perfectly definite idea of the precise powers that must be vested in an individual in order to save that world from anarchy. Yet Tiberius can pretend to hesitate, not merely about assuming the office, but about the nature of the office which he assumes;[1676] and, although on the accession of his successor, Gaius Caesar, the _soliti honores_ were conferred _en bloc_, yet the idea that the creation of a Princeps was an act of special investiture always clung to the office. It was obvious so far as the choice of the person was concerned, but it even affected the powers conferred, and we have seen that the grants made to Emperors of the second and third centuries were in all probability different, both in form and in matter, from those made to Emperors of the first.[1677] The electing body was the Roman people, chiefly represented by the Senate but still retaining in its own hands the formal ratification of most of the powers conferred. But the powerlessness of this sovereign is of the very essence of the history of the Principate. As a rule, all that it can do is to recognise an _imperium_ already established by the army, whether this establishment be due to the tacit consent of praetorians or legionaries or to the active use of their swords. The crucial point in the creation of an emperor is his salutation by his army as _imperator_. Such a salutation did not mean that the general who accepted it was Princeps; it meant only that he was a candidate for the Principate. The act itself was one of revolution; its legality depended upon its success. Did the legions in other provinces accept the candidature, the Senate immediately fulfilled its formal task; did rival aspirants meet in battle, it was always ready to welcome the survivor. To be truly a Princeps was to receive the customary honours and offices from the Senate, and Vitellius was acting in the true spirit of the constitution when he adopted as the formal date of his accession (_dies imperii_) the day on which his claims had been ratified by the fathers.[1678] Vespasian was acting contrary to that spirit when he regarded as the beginning of his the moment at which he had been saluted _imperator_ by the legions of Egypt.[1679]