Lucius Aelius Sejanus, Roman politician (born 20 BC)

AD 31 (XXXI) was a common year starting on Monday of the Julian calendar. At the time, it was known as the Year of the Consulship of Tiberius and Sejanus. The denomination AD 31 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

Lucius Aelius Sejanus, commonly known as Sejanus, was a Roman soldier and confidant of the Roman Emperor Tiberius. Of the Equites class by birth, Sejanus rose to power as prefect of the Praetorian Guard, the imperial bodyguard, of which he was commander from AD 14 until his execution for treason in AD 31.