“…the emperor became a cruel tyrant, as well as an abettor of cruelty in others. Of this the cause and origin was Aelius Sejanus.” (Tacitus)1
The beginning of the end for Tiberius was due to the would be usurper Sejanus’ plot to take the throne. Tiberius was a distrustful and private emperor who held one man in confidence above all others, this man was Aelius Sejanus. Sejanus was the low born Praetorian prefect who had won the emperors favor due to Tiberius’ military background. Sejanus used his position to advance in the world by conspiring against Tiberius son, Drusus. Sejanus and Drusus had long held each other in enmity since their time in Pannonia putting down a rebellion. Sejanus first attempt at the throne was by betrothing his daughter to the son of Claudius, who was Tiberius nephew. This plan was thrown awry when Claudius son accidentally died.
In the year 23 the long feud between Drusus and himself grew to a head when during an argument Drusus struck Sejanus in the head and declared, “A stranger was invited to assist in the government while the emperor’s son was alive.” (Tacitus) This enraged Sejanus enough to plot the death of Drusus through the slow use of poison in the hopes that it would pass as natural causes. Sejanus was able to corrupt Drusus wife, Livilla, and hoped to use their affair, and his plans to marry her in the future, to finally enter into the struggle for the throne. It is curious Livilla would betray her husband and the security of him being guaranteed the position for emperor for the risk of following after Sejanus who may never be emperor and was clearly using her. By September of that year Sejanus plan had come to fruition and Drusus had died by what seemed to be natural causes. This was incredibly damaging to Tiberius already jaded view of the role of the princeps and led to him being even more withdrawn from politics and the people. When Sejanus brought the subject of marriage to Tiberius he was quickly shut down and warned that he was over stepping his bounds.
After this plan failed Sejanus decided to turn Tiberius against the senate by playing off his latent mistrust of others. His constant goading drove Tiberius to leave to city of Rome and spend his days in Campania in the year 26 and eventually the island of Capri where he stayed until his death. With Sejanus alone in Rome he was free to act how he saw fit and remove anyone he say as a threat to his power, killing many people, including all but one of Germanicus sons, the future emperor Claudius. It is believed that Sejanus tried to win the favor of the Julii and over throw Tiberius. When Tiberius found out about Sejanus’ plotting he had to find a way to stop him without alerting Sejanus to his plan and fighting back. He sent many contradictory letters in order to confuse enemy and ally alike, the last of which summoned Sejanus to a senate meeting where the rest was read demanding his immediate arrest and execution.
Sejanus was tried and sentenced, his body thrown down the Gemoian Stairs where it was torn to pieces by the mob. Riots ensued where anyone in the streets linked to his tyrannical reign was brutally murdered. For a period of time almost every ally of Sejanus was tried for treason and it is then that the truth of Drusus murder was revealed when Apicata, Sejanus ex-wife, revealed every part of the plot including Livilla who according to Cassius Dio was locked in a room by her mother and starved to death. It is in this time that Tiberius set a precedent of tyranny by trying everyone associated with Sejanus for treason and having them all killed.
Sejanus suffered posthumously for his crimes through the punishment of Damnatio memoriae wherein all of his statues and his name removed from public records.