He ultimately gained such influence over Tiberius that this suspicious man, who was close and reserved to all mankind, opened his bosom to Seianus, and made him his confidant. For many years he governed Tiberius; but, not content with this high position, he formed the design of obtaining the imperial power. With this view he sought to make himself popular with the soldiers, and gave posts of honour and emolument to his creatures and favourites. With the same object he resolved to get rid of all the members of the imperial family. He debauched Livia, the wife of Drusus, the son of Tiberius; and by promising her marriage and a participation in the imperial power, he was enabled to poison Drusus with her connivance and assistance (A.D. 23).
An accident increased the credit of Seianus, and confirmed the confidence of Tiberius. The emperor, with Seianus and others, was feasting in a natural cave, between Amyclae, which was on the seacoast, and the hills of Fundi. The entrance of the cave suddenly fell in and crushed some of the slaves; and all the guests, in alarm, tried to make their escape. Seianus, resting his knees on the couch of Tiberius, and placing his shoulders under the falling rock, protected his master, and was discovered in this posture by the soldiers who came to their relief.
After Tiberius had shut himself up in the island of Capreae, Seianus had full scope for his machinations; and the death of Livia, the mother of Tiberius (A.D. 29), was followed by the banishment of Agrippina and her sons Nero and Drusus. Tiberius at last began to suspect the designs of Seianus, and felt that it was time to rid himself of a man who was almost more than a rival. To cover his schemes and remove Seianus from about him, Tiberius made him joint consul with himself in A.D. 31. He then sent Sertorius Macro to Rome with a commission to take the command of the praetorian cohorts. Macro, after assuring himself of the troops, and depriving Seianus of his usual guard, produced a letter from Tiberius to the Senate, in which the emperor expressed his apprehensions of Seianus. The consul Regulus conducted him to prison, and the people loaded him with insult and outrage. The Senate on the same day decreed his death, and he was immediately executed. His body was dragged about the streets and finally thrown into the Tiber. Many of the friends of Seianus perished at the same time, and his son and daughter shared his fate (Tac. Ann. iv. 41-59; 74; v. 6-9; Suet. Tib.; Dio Cass. lvii., lviii.; Juv.x. 65-86).
The story of Seianus is the subject of a play by Ben Jonson, entitled Sejanus, produced in 1603. (Harpers Dictionary of Classical Antiquities)
Chief administrator of the Roman Empire for the emperor Tiberius, alleged murderer of Tiberius' only son, Drusus Caesar, and suspect in a plot to overthrow Tiberius and become emperor himself.
Sejanus was related through his mother to the distinguished senatorial family Cornelii Lentuli. In AD 14, upon the accession of Tiberius, he joined his father, Seius Strabo, as prefect of the Emperor's household troops, the Praetorian Guard, and became sole prefect a year or two later. As prefect he gained the complete confidence of the Emperor.
After the death of Drusus (AD 23), he began systematically to attack the position of Drusus' mother, Agrippina the Elder, whose sons were Tiberius' probable heirs. In 25, Sejanus was refused Tiberius' permission to marry Drusus' widow, Livilla, who may have been Sejanus' accomplice in the poisoning of her husband. In 27, however, Sejanus persuaded the Emperor to take up residence on Capreae (modern Capri) and in 29 succeeded in having Agrippina and her son Nero exiled.
As consul (31), with the prospect of attaining the great administrative prerogatives of tribunician power, Sejanus fell under the suspicion of the emperor. Tiberius, repeatedly warned by his sister-in-law Antonia of Sejanus' designs, had him arrested and executed. The Senate and the populace rejoiced as his body was dragged through the streets, and a long reign of terror ensued against his adherents. (Encyclopedia Britannica)
A Roman statesman, born at Vulsinii in Etruria. He was the son of Seius Strabo, who was commander of the praetorian troops at the close of the reign of Augustus, A.D. 14 (Tac. Ann. iv. 1). In the same year Seianus was made the colleague of his father in the command of the praetorian bands; and upon his father being sent as governor to Egypt, he obtained the sole command of these troops.