Lucius Aelius Sejanus (or Seianus) (20 BC– October 18, 31 AD) was an ambitious soldier, friend and confidant of Tiberius, and for a time the most influential and feared citizen of Rome.
Sejanus was born at Volsinii, in Etruria, to the family of Lucius Seius Strabo, a knight who became praetorian prefect under Augustus. By Roman custom he was known as Aelius Sejanus after his adoption into the more prestigious Aelian gens.
He was appointed praetorian prefect on the accession of Tiberius, as the colleague of his father. On his father's appointment to the governorship of Egypt in 15, he became sole commander of the Praetorian Guard, and began to increase his power.
After the death of Tiberius' son Drusus in 23, Sejanus consolidated his power over the Senate, and concentrated the scattered elements of the Praetorian guard into a single camp outside the Viminal Gate of Rome. Despite failing in an attempt to marry Drusus' widow Livilla in 25, which would have made him part of the ruling house, he increased his power further upon Tiberius' retirement to Capri in 27.
In 31, despite his equestrian rank, he shared the consulship with Tiberius, and finally received permission to marry Livilla. Sejanus felt his position was unassailable, and plotted to seize power for himself. Tiberius discovered the plot, however, and Macro, prefect of the Vigiles, arrested him. After Sejanus was executed, Macro succeeded him as commander of the Praetorian Guard. Many of Sejanus' friends and allies were executed or committed suicide after his fall. His three children were killed; his divorced wife, Apicata, killed herself after accusing him and Livilla of poisoning Drusus.
Sejanus in literature
Ben Jonson made the story into a 1603 play entitled Sejanus, His Fall. Sejanus was played by Patrick Stewart in the TV adaptation of Robert Graves's book I, Claudius.
Sejanus' fall from power is recounted in detail by Roman historians, particularly Tacitus.