The death of Drusus on September 14th AD 23 left Tiberius without a direct heir. It had considerable implications for the imperial family.
Normally, we (as indeed would many of the ancient commentators) would be sceptical about any accusation of poisoning. People died suddenly in antiquity. People died young. Medical science was very basic. Mostly, there was no way of knowing why someone died (unless they were stabbed or strangled or beheaded, the last of which tends to be relatively clearly marked on the corpse). So, when a powerful individual died, there was often a temptation to look for a hidden hand behind the death.
But merely because the evidence is shaky, it doesn’t mean poisoning was not employed. It seems very likely that the emperor Claudius was poisoned. And, in this instance, as well, the evidence points to poison. Tacitus, normally sceptical about such gossip, believes it to have been so.
The story of the discovery of the poisoning is horrific and retold in Dio, 58.11 and Annales 5.9. Sejanus fell from power. He was killed, as was to be expected. But his young children were also murdered. The boy knew what was happening, but his sister was too young. Stories circulated that she raped before being strangled since in a perverse operation of legal and religious custom, it was not allowed to execute a virgin. When the news reached Apicata, their mother, she killed herself, and left a note in which she accused Sejanus and Livilla, sister of Germanicus and wife of Drusus, of having conspired to poison Drusus.
Livilla and Sejanus were rumoured to be lovers, and to have been lovers from before Drusus’ death. Secrets of imperial bedrooms can rarely be kept, but gossip and rumour must have followed the imperial family around. Truth is difficult to reach. There was a persistent theme under the early emperors of the formation of political relationship through sexual relationships, notable in the career of Messalina. Yet, what easier way was there of ruining the reputation of an imperial princess than making allegations about her sexual promiscuity?
This was evidently more than a case of a bereaved and suicidal mother having one last act of revenge. Tiberius has the slaves in Drusus’ household tortured. Two of them, Eudemus and Lygdus, a eunuch, confessed to having poisoned Drusus with a slow-acting poison, so that it would like an extended illness (Annales 4.8; Annales 4.10-11). The story of the affair came out.
In retrospect, the most obvious beneficiary was Sejanus. He had removed the emperor’s son, a man openly hostile to him. This meant that Tiberius had no adult male member of the family on whom to rely. But as the senators wept for the loss of Drusus (and perhaps also were remembering the recent loss of Germanicus), Tiberius ordered the sons of Germanicus to be brought into the senate house. These he commended to the senators, as he had commended them to the trust of their uncle, Drusus. It was evident that they were now expected to succeed Tiberius to the throne (Annales 4.8).
This is one of the oddities of the episode. Drusus had children, Julia and Tiberius Gemellus. The latter was still young, having been born in late 19 (Annales 2.84), soon after the death of Germanicus. Julia was about 18 on the death of her father and probably already married to another Drusus, the son of Germanicus. It was the Germanican line, directly descended from Augustus, on which the imperial family rested its hopes.
To have a chance of imperial power, Sejanus needed to insert himself into the imperial family. He had already betrothed his daughter to Claudius’ son. But he would need a brilliant marriage himself, to take him to the heart of the family. His most obvious predecessor, Agrippa, had married Julia, the emperor’s daughter. He also needed to remove the competition: the sons of Agrippina and Germanicus
In spite of all this very obvious familial and court politics, Tiberius finished his speech to the senate on Drusus’ death by hoping for a return to the Republic. Tacitus imagines the senators’ bewilderment (Annales 4.9).
But without a family member to support him, Tiberius came to rely more on Sejanus. Sejanus was able to enhance his position and authority in Rome and achieve something close to dominance.