Gaius Maecenas
Sejanus was born in 20 BC at Volsinii, Etruria, into the family of Lucius Seius Strabo. The Seii were Romans of the equestrian class (or knights), the lower of the two upper social classes of the Roman Republic and the early Roman Empire. Sejanus' grandfather maintained relations with senatorial families through his marriage with Terentia, a sister of the wife of Gaius Maecenas, who was one of Emperor Augustus' most powerful political allies.