For Tiberius, the public recognition of another potential successor could only increase his freedom of manoeuvre vis-a-vis the children of
Agrippina. For Sejanus, on the other hand, the elimination of Agrip- pina's children as candidates was essential for the success of his dynasdc ambitions. Nero and Drusus were accused of plotting against the emperor by a relative of Sejanus, Cassius Longinus (probably Lucius, who was consul ordinarius in a.d. 30, rather than his brother Gaius, the famous jurist (see ch. 21), who was a suffect consul in the same year). The fact that the Cassii Longini were related to the Caesaricide Cassius did not make them republicans, though that was what Gaius was to be accused of by Nero after the conspiracy of Piso many years later. The threat posed by Nero and Drusus to Tiberius and to the succession of Gemellus (with or without Sejanus as his stepfather) was real. Even after the elimination of Sejanus, Tiberius took no steps to release Drusus from prison. It is likely that Agrippina and her sons, seeing the danger that Sejanus represented, thought it necessary to plan for Tiberius' removal before Sejanus' position had become unchallengeable.
It was Germanicus' mother the younger Antonia, the young men's grandmother, who warned Tiberius in a letter delivered to him personally through her freedman M. Antonius Pallas that Sejanus' consolidation of his power was not just aimed against Agrippina and her children, but beginning to threaten Tiberius' own chances of polidcal survival. With Sejanus as protector of Tiberius' heir, and no other candidates for the Principate surviving, Tiberius' own role would have been played out. And given that it was Sejanus who was responsible for Tiberius' personal security, Antonia must have pointed out to him that Sejanus would have no further interest in keeping Tiberius alive once Agrippina and her offspring no longer existed. It was a powerful argument, and Tiberius summoned Germanicus' remaining son, Gaius Caligula, to the safety of his household at Capri. He did not prevent Sejanus from executing Nero.
In over seventeen years as emperor, Tiberius had not ordered the execution of one single senator. The old man's well-planned and efficient elimination of Sejanus on 18 October a.d. 31 consequently came as a great shock to Rome. His agent was another equestrian public servant, Sutorius Macro, prefect of the urban vigiles: he brought two letters from Tiberius. One was read out to the Senate in Sejanus' presence; it was lengthy and impenetrable (in Juvenal's words, 'grandis et verbosa') and only after a long time did it come to the point: Sejanus was denounced as a traitor. While the Senate, and Sejanus himself had been kept guessing, Macro took command of the praetorians, authorized by Tiberius' second letter. Sejanus had expected to be granted tribunicia potestas as Tiberius' colleague. Instead he found himself stripped of his office and arrested. He was executed the same day; so were his wife and daughter. It was claimed that eight years before, Sejanus and Livilla had together poisoned Tiberius' son, Livilla's husband Drusus.
Sejanus' fall enabled a number of figures who had been supporters of Germanicus to return to the centre of the political stage, under the protection of the younger Antonia. Some of them were to give support to the regimes of her grandson Caligula, and then her son Claudius. Lucius Vitellius, who was to become Claudius' principal adviser and the father of another later emperor, was consul ordinarius in a.d. 34, and in 3 5 a suffect consulship was held by his friend Valerius Asiaticus from Vienne, whose son was to be betrothed to the emperor Vitellius' daughter, and whose grandson was to be a powerful figure into the next century (M. Lollius Paulinus Decimus Valerius Asiaticus Saturninus, cos. a.d. 94, cos. II a.d. 125). Flavius Sabinus {praefectus urbi under Nero, Otho and Vitellius, and the brother of Vespasian), entered the Senate in a.d. 34 or 3 5. Galba has already been mentioned; his successor as suffect consul in a.d. 3 3 was Lucius Salvius Otho, whose father, a novus homo, had reached the praetorship early in Tiberius' reign as a result of the favour of Livia. Otho's daughter had once been betrothed to Germanicus' son Drusus; his elder son Lucius Titianus was to reach the consulship in 5 2, become proconsul of Asia, and like his father, promagister of the Arval Brethren; his younger son became emperor.[417]
On the other hand the overthrow of Sejanus did not make any difference to Tiberius' hostility to Agrippina herself. Neither she nor Drusus were released from prison or exile, and they both died in a.d. 33. Her daughters could be made harmless without being killed. In 33, Tiberius married Drusilla to Lucius Cassius Longinus, and Germanicus' youngest daughter, lulia Livilla, to the powerful and loyal Marcus Vinicius; his grandfather, the consul of 19 B.C., had been one of Tiberius' early generals in Illyricum and won the ornamenta triumphalia for his services in Germany. The father, consul ordinarius in a.d. 2, was highly regarded as an orator; Vinicius himself had been consul in a.d. 30 (the year in which Velleius Paterculus dedicated his history to him), and perhaps was among those who felt insulted, if not threatened, by Sejanus' predominance. By entrusting Livilla to him, Tiberius was marking him out as someone to whom the empire too might be entrusted; and indeed (despite Caligula's banishment of Livilla in 39)
Vinicius was powerful enough to be the major contender for the succession after Caligula's removal in 41. The third daughter, Agrippina the Younger, had already been married in a.d. 28, to Cn. Domitius Ahenobarbus (cos. a.d. 52). Through his mother Antonia the Elder, he was the grandson of Mark Antony and Augustus' sister Octavia. It is hardly surprising that the couple avoided having children so long as Tiberius was alive. Only in the last year of Tiberius' life was Ahenobarbus exiled on a charge of incest with his sister, Domitia Lepida. Tiberius also forced Asinius Gallus to end his life in a.d. 33, after three years of house-arrest. Tiberius' hatred for him went much further back than Gallus' association with Agrippina and alleged support for Sejanus. Nevertheless three of his sons survived to take office again under Caligula (Servius Asinius Celer, cos. 38, executed in 47; Asinius Gallus, banished in 46; and Asinius Pollio, proconsul of Asia 38/39).
Tacitus notes that the attacks on Sejanus and Livilla in the Senate were led by 'men with the great names Scipio, Silanus, Cassius'. If Tacitus wished to imply that the political significance of these men derived from their republican ancestry, that was not the whole story. Their links with the domus Caesaris mattered as much, if not more. These men, and others, used the freedom provided by Tiberius' absence from Rome to indulge in an orgy of recrimination, accusing their personal opponents of having been associated with Sejanus. Some of those who suffered were no doubt indeed close associates of Sejanus - though it is interesting that even his uncle, Quintus Iunius Blaesus, was not formally condemned and executed, but committed suicide after Tiberius renounced his amicitia. Blaesus' two sons even survived until 36. Indeed, some of those keenest to attack Sejanus' memory were related to him: the grandfather of the two Cassii, Quintus Aelius Tubero, had been Sejanus' stepfather. The trials of the next few years were certainly not the result of any plan by Tiberius to round up those who had participated in Sejanus' 'conspiracy' against him: there had been no such conspiracy.
But it suited other political figures to suggest that there had. The charge of association with Sejanus was used as a cover for political, family and personal hatreds in such a way as to give the impression that there must have been a major conspiracy organized by Sejanus in which half the Senate had been involved. Rumour exaggerated his power to such an extent that it was even said that Tiberius had given instructions that, if Sejanus' supporters in the praetorian guard posed a threat, Germanicus' children might have to be released from prison to act as a rallying-point for those loyal to the dynasty. But the minute number of those directly convicted of being Sejanus' associates suggests that they were not executed for being conspirators, but because they might resent the way in which a loyal servant and his wife and daughter had been dealt with by Tiberius. Had Sejanus managed to remove all the offspring of Germanicus, he might have been a real threat to Tiberius. As it was, the conspirator was not Sejanus, but Tiberius.