Through years of crafty intrigues and indispensable service to the emperor, Sejanus had worked himself up to become the most powerful man in the empire. Exactly what caused his sudden downfall is unclear: According to Josephus, it was Antonia, the mother of Livilla, who finally alerted Tiberius to the growing threat Sejanus posed. She sent a letter to Capri in the care of her freedman Pallas.