For nearly two decades, Lucius Aelius Sejanus built his position alongside Emperor Tiberius, becoming the most powerful man in Rome after the ruler himself. His downfall in October 31 CE was as spectacular as his rise. Who was the man who transformed the Praetorian Guard into a tool of political control and almost seized supreme power?
An Equestrian with Great Ambitions
Sejanus was born around 20 BCE in the Etruscan city of Volsinii, into a family of the equestrian order. This was the second highest social class in Roman hierarchy, but for someone with truly imperial ambitions, it represented a glass ceiling. His father, Lucius Seius Strabo, managed to reach the position of Praetorian Prefect during Augustus’s reign, opening doors to high politics for his son.
Sejanus’s family was not without powerful connections. His grandfather maintained close relations with senatorial families through marriage to Terentia, sister of Gaius Maecenas’s wife, one of Augustus’s strongest political allies. These connections would prove invaluable in Sejanus’s subsequent career.
A key moment in his life was his adoption into the Aelius family, one of the more prestigious Roman families. According to Roman custom, he then took the name Lucius Aelius Sejanus. Such adoptions were common as a means of social advancement and building political alliances in ancient Rome.
Architect of the New Praetorian Guard
When Tiberius became emperor in 14 CE, he appointed Sejanus as Praetorian Prefect alongside his father. This was standard procedure to ensure command continuity, but Sejanus quickly became much more than a loyal executor of orders. When Strabo was appointed governor of Egypt in 15 CE, his son remained sole commander of the most powerful military formation at the empire’s heart.
It was then that Sejanus began reforms that forever changed the character of the Praetorian Guard. Previously, Praetorian cohorts were dispersed across different locations in and around Rome. Sejanus consolidated all units into one military camp, creating a concentrated force in the capital’s center. This had far-reaching consequences, transforming the guard from the emperor’s personal bodyguard into a potent political tool capable of intervening in every sphere of public life.
Sejanus’s reforms extended far beyond the military. Under his leadership, the guard began to involve itself in public security, civil administration, and eventually, direct political intervention as well.
These changes outlived Sejanus himself, shaping the exercise of imperial power in Rome for centuries. Many historians believe he created the model by which the Praetorians later deposed and elevated emperors.
Master of Court Intrigues
Sejanus enjoyed complete trust from Tiberius and used this to systematically eliminate potential rivals. His main targets were members of the imperial family who could challenge his influence or block his path to even greater power. The sons of Germanicus and Agrippina the Elder, Nero and Drusus, fell victim to his intricately woven schemes.
The darkest chapter in Sejanus’s biography involves his alleged role in the death of Drusus the Younger, Tiberius’s only son. For years, Sejanus had an affair with Julia Livilla, Drusus’s wife.
According to ancient sources, the pair allegedly poisoned her husband in 23 CE. Rumors went even further, suggesting that the real father of Gemellus, Tiberius’s official grandson, was none other than Sejanus. Today, it is difficult to determine how much truth lies in these accusations, and how much is later propaganda to justify his downfall.
His methods towards inconvenient senators were equally ruthless. He organized fabricated accusations and show trials, exploiting the atmosphere of suspicion pervading Tiberius’s reign. The system of delatores—paid informers—flourished under his patronage, paralyzing Roman political life with fear of false charges of treason.
The Shadow Ruler
The turning point in Sejanus’s career came in 26 or 27 CE, when Tiberius made the surprising decision to retire to the island of Capri. The emperor, tired of court intrigues and beset by growing paranoia, withdrew from state duties. Sejanus remained in Rome as the de facto administrator of the empire, controlling access to the ruler and filtering all information sent to the island.
For the next several years, the Praetorian Prefect was the most powerful and feared citizen of Rome. His authority had virtually no limits, and his ambitions grew alongside his influence. Anyone wishing to obtain anything from the emperor first had to go through Sejanus. Senators sought his favor, and those who lost it faced trial and execution.
Already in 25 CE, Sejanus attempted to formalize his position by marrying Livilla, but Tiberius refused. Marriage to the widow of the imperial son would have made him a member of the ruling family and a potential contender for the throne. Despite his trust in the prefect, Tiberius was not ready to so radically elevate his status. Sejanus had to wait several more years for his ambition to be realized.
The Pinnacle and the Chasm
The year 31 seemingly fulfilled all of Sejanus’s dreams. He served as consul with Tiberius – the highest office in the Roman Republic, still prestigious despite its lack of real power. Furthermore, the emperor finally approved his marriage to Livilla. Sejanus must have felt he had achieved everything he dreamed of in nearly two decades of arduous climb.
At that very moment, convinced of his unreliably secure position, the prefect allegedly began plotting a coup. He wanted to seize absolute power for himself, no longer sharing it with the aging emperor. This was the mistake that would cost him his life.
Antonia Minor, mother of Germanicus and one of Rome’s most respected women, warned Tiberius of his trusted minister’s plot. The emperor, responding with uncharacteristic speed and decisiveness, used Macro, an officer of the guard, to carry out Sejanus’s arrest. The whole event unfolded on October 18, 31 CE at a Senate meeting, where a letter from the emperor was read – starting with praise for the prefect, but ending with the command for his arrest.
The Final Reckoning
Sejanus’s fall was swift and complete. The very day he was arrested, the Senate sentenced him to death. The man before whom all Rome had trembled that morning was dead by evening. Macro, who conducted the operation, immediately assumed his post as Praetorian Prefect, proving the system built by Sejanus functioned perfectly well without its creator.
The consequences of the prefect’s fall hit everyone associated with him. His friends and supporters were hunted down and killed in a wave of repressions that swept Rome in the following months. Sejanus’s three children were executed to erase even the memory of his bloodline. Apicata, his former wife, committed suicide but left a note in which she revealed details of Drusus the Younger’s poisoning.
Autor
Rory Thornfield
Rory's grandfather left behind a wartime diary filled with accounts of a minor Burma skirmish that history books never mentioned. Reading it, Rory realized: behind every famous battle are dozens of forgotten struggles, each with its own human drama.
His preferred topics: The overlooked corners of military history – secondary campaigns, shadow battalions, local conflicts that never made headlines. From medieval sieges to twentieth-century expeditions, he focuses on the soldiers, not the generals. The people who faced impossible choices and carried those experiences forever.
Rory strips away the romanticism without losing respect for those who served. He combines tactical analysis with personal stories, examining human endurance and moral complexity rather than celebrating warfare. His writing is balanced, thoughtful, and deeply researched.
Outside work, Rory visits forgotten battlefields (now quiet farmland), photographs war memorials nobody tends anymore, and interviews veterans' families.