Sejanus (Lucius Aelius Sejanus) sĭjā´nəs [key], d. AD 31, Roman statesman; son of Sejus Strabo, Praetorian prefect. When his father went to Egypt as governor, he succeeded to the command of the Praetorian Guards and obtained great ascendancy over Emperor Tiberius . He was suspected of conspiring (AD 23) with Livilla in a successful plot to poison her husband, the emperor's son Drusus. He obtained (AD 29) the arrest of Agrippina the Elder . Sejanus was put to death by Tiberius, who feared that he was plotting against him.

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