Sejanus holds the consulship with Tiberius in absentia in 31, receives the long-sought permission from Tiberius to marry Drusus’s widow Livilla and begins his play for power in earnest.

In the same year, the Emperor receives evidence from Antonia Minor, his sister-in-law, that Sejanus plans to overthrow him.

Precisely what happened is difficult to determine, but Sejanus seems to have covertly attempted to court those families who were tied to the Julians, and attempted to ingratiate himself with the Julian family line with an eye towards placing himself, as an adopted Julian, in the position of Princeps, or as a possible regent.

Livilla is later implicated in this plot, and is revealed to have been Sejanus's lover for a number of years, possibly even before the birth of the twins, who some (including Tiberius) suspect Sejanus to have fathered.

The plot seems to have involved the two of them overthrowing Tiberius, with the support of the Julians, and either assuming the Principate themselves, or serving as regent to the young Tiberius Gemellus or possibly even Gaius Caligula.

Those who stand in his way are tried for treason and swiftly dealt with.

Sejanus is summoned in early October to a meeting of the Senate, where a letter from Tiberius is read condemning Sejanus and ordering his immediate execution.

Sejanus is tried, dragged off to prison,and he and several of his colleagues are executed within the week.

As commander of the Praetorian Guard, he is replaced by Naevius Sutorius Macro, who, according to Tacitus, had been active in discrediting Sejanus and in directing the subsequent purge against his family and followers, with most of Sejanus' family (including his children) and followers sharing his fate.

Sejanus' former wife Apicata, on hearing of the death of her children, addresses a letter to Tiberius, accusing Sejanus and Livilla of having poisoned Drusus; she then commits suicide.

Drusus' cupbearer Lygdus and Livilla's physician Eudemus are questioned and under torture confirm Apicata's accusation.

Livilla dies shortly afterwards, either being killed or by suicide.

According to Cassius Dio, Tiberius handed Livilla over to her mother, Antonia Minor, who locked her up in a room and starved her to death.

Tacitus claims that more treason trials followed and that whereas Tiberius had been hesitant to act at the outset of his reign, now, towards the end of his life, he seemed to do so without compunction.

Hardest hit were those families with political ties to the Julians.

Even the imperial magistracy was hit, as any and all who had associated with Sejanus or could in some way be tied to his schemes were summarily tried and executed, their properties seized by the state (in a similar way, in the few years after Valeria Messalina's death, Agrippina the Younger removed anyone she considered loyal to Messalina's memory, much in the same way that Sejanus's followers were executed).

Several modern historians have challenged Tacitus' portrayal of a tyrannical, vengeful emperor.

The prominent ancient historian Edward Togo Salmon notes: "In the whole twenty two years of Tiberius' reign, not more than fifty-two persons were accused of treason, of whom almost half escaped conviction, while the four innocent people to be condemned fell victims to the excessive zeal of the Senate, not to the Emperor's tyranny".

(A history of the Roman world from 30 B.C.

to A.D. 138 (1944; rev.

ed.

1963, 1968; p. 183) One of the few surviving sources contemporary with the rule of Tiberius comes from Velleius Paterculus, who served under Tiberius for eight years (from CE 4) in Germany and Pannonia as praefect of cavalry and legatus.

Paterculus' Compendium of Roman History spans a period from the fall of Troy to the death of Livia in CE 29.

His text on Tiberius lavishes praise on both the emperor and Sejanus.

How much of this is due to genuine admiration or prudence remains an open question, but it has been conjectured that he was put to death in CE 31 as a friend of Sejanus.