The people of ancient Rome knew of a tragic hero Drusus (Drusus the Elder), the younger brother of Tiberius who died in a campaign. But there was another, younger and lesser known, Drusus in Tiberius’ family. He was Nero Claudius Drusus (Drusus the Younger, nicknamed Castor), the only son of Tiberius. The elder Drusus may have been a hero, but Castor seemed to be mostly overlooked first by his own family, as well as future historians.

Born from the union of Tiberius, stepson of Augustus and Vipsania, daughter of Marcus Agrippa, Castor seemed to be well-positioned for greatness. His marriage to Livilla, the granddaughter of Mark Antony and the sister of Germanicus also strengthened his place within the imperial family. However, these advantages, as well as the fact that Castor himself was a capable statesman, did not serve him at the end and he was easily eclipsed by Germanicus. His death, rumoured to be by poison in the hands of his own wife, aroused no suspicions at the time, which may be an indication of his poor health.
Who was Castor, Really? Finding Castor in the Ara Pacis Augustae
What we know of Castor are mostly pieced together from the lives of his relatives who took center stage as well as from ancient historians such as Suetonius and Tacitus who would give him a brief mention or compare him unfavorably to Germanicus. However, his handling of the mutiny after the death of Augustus has proven him to be as capable a leader as Germanicus – if not more so. The nickname Castor linked him to one of the divine guardians of Rome and possibly became one of the factors which strengthened his father’s position in Ancient Rome.

Thomas de Quincey, in The Caesar, wrote that “Tiberius left no children; but Drusus, the younger of the two brothers, by his marriage with the younger Antonia, (daughter of Mark Anthony,) had the celebrated Germanicus, and Claudius, (afterwards emperor)” – of course, he was proven to be mistaken in regards to the existence of Tiberius’ son, but he may be forgiven as examinations of the Ara Pacis Augustae also left scholars arguing about the identity of the young figure standing near the figure of Tiberius and the lady standing near them.
It is in connection with these figures that scholars have been facing a difficulty. The Ara Pacis was erected ceremoniously on 4 July 13 BCE, and dedications were made to it annually by the public as it represented the imperial family. Therefore, the relief would have very likely needed to be kept up to date. However, the imperial family has undergone a series of changes after from Agrippa’s death in 12 BCE, which drastically changed Tiberius’ own status and familial relationships.

Scholars, recognizing the family group of Tiberius in 13 BCE as unchanged, included Tiberius’ first wife Vipsania. The woman in the background, whose hand rests on the boy’s head, is identified as her aunt, Agrippa’s sister, Vipsania Polla. The boy was identified as Agrippa’s own son, Lucius, instead of Tiberius’ son, Castor. However, Lucius and his brother Gaius had actually been adopted by Augustus in 17 BCE and would have realistically be placed nearer their adoptive father. Castor, Tiberius’ only son, is not mentioned.
Other scholars conclude the designer to be making necessary adaptations to the Ara Pacis as occasion demanded. They therefore recognize the lady as Julia, Augustus’ daughter and the second wife of Tiberius. The feminine figure in the background becomes a nurse to the boy, who was still identified as Lucius. The question of the presence or absence of Castor is again not raised.

This view would have perhaps led to the less offensive identifications at the time. No doubt that the presence of Vipsania as the wife of Tiberius on a monument erected in the emperor’s honor would have been an offense to the emperor after Tiberius’ marriage with his daughter Julia. Due regard was likely had for the imperial family with the result that the figure originally designed as Vipsania was remodelled as Julia.
If we were to identify the little boy as Castor, we would recognize the skilful treatment of a difficult problem, which was that of representing Castor with Tiberius and Julia in such a manner as to suggest that Julia is not his mother. The boy’s pose indicates his connection with his father and stepmother. But the maternity of Julia is subtly discounted by the device of permitting the nurse in the background to lay her hand on his head, while Julia maintains a restrained, albeit kindly, attitude toward him.

A matter of succession: The political rise and marriages of Tiberius
Before adopting Tiberius, Augustus had adopted his own two grandsons who were born from the union of his right-hand man Marcus Vipsanius Agrippa and his daughter Julia. However, there were no hint in any surviving text of the birth names of his grandsons, Gaius and Lucius Caesar. This may mean that either they were never referred to by their birth father’s name, or that their birth names were suppressed as soon as Augustus adopted them. Augustus himself had been born Gaius Octavius and, at the age of eighteen, had taken the name of his great-uncle to become Gaius Julius Caesar. Although he was briefly known as Octavian, there was never any public document which refers to him as the cognomen Octavianus. That is, Augustus had systematically suppressed the memory of former family ties within the “Julian” family he had created and imposed on the Forum – and he did precisely this to the people who he looked upon as his successors.
In his youth, Tiberius was married to Vipsania Agrippina, daughter of Marcus Vipsanius Agrippa. After the death of Agrippa in 12 BCE, Augustus commanded Tiberius to divorce Vipsania in order to marry Julia. According to Suetonius, Tiberius divorced Vipsania in 11 BCE. Later, with the death of Gaius and Lucius, Augustus reluctantly recognized Tiberius as his successor. Although he was the last resort as heir to Augustus, Tiberius was an able commander. By 20 BCE he was evidently high enough on the military rankings to be able to accompany Augustus to the east to reclaim the standards lost to the Parthians by Crassus thirty-three years earlier. He was appointed governor of Gaul in 16 BCE and given his first consulship three years later.

Augustus adopted Tiberius in 4 CE and named him as his successor. However, as a part of his adoption, Tiberius was required to adopt Germanicus – making Germanicus his imperial successor instead of his own son, Castor. This was a deliberate decision by Augustus, who had shown a pattern of suppressing old familial relationships after adoptions and therefore would have wanted to distance Tiberius from his “old” family. Another, more important, reason was that Augustus wanted to keep his successors in his own bloodline. The two sons of Agrippa and Julia would have continued the Julian blood if they had lived long enough to succeed him. Tiberius, who was of Claudian descent, did not fit this requirement. He therefore needed to marry Julia and beget children from her. However, it was soon apparent that Augustus would never have any Julian-blooded grandchildren from this union. He therefore turned to Germanicus who, despite also being a Claudian descent, was married to Augustus’ own granddaughter Agrippina who was of Julian blood and has produced more than one heirs of his own blood for future successors. Castor did not fit in in this plan. Castor’s marriage to Germanicus’ sister Livilla, who was of the Claudian branch of the family, made him and his own children ineligible for any consideration of being Augustus’ successor.

The Divine Twin in Tiberius’ rule
The popular legend in regards to the nickname Castor – a patron god of the praetorian guards, is that it was an ironic nickname given to Drusus the Younger after a he came to blows with one of the guards. Indeed, Castor is traditionally depicted as hot headed and quick to anger. However, there is another dimension to this nickname which made it possible that he was already called Castor much earlier than the altercation with the Praetorian Guard. His father, Tiberius, was an ardent lover of myth who was especially interested in the twin gods, Castor and Pollux, particularly their life of constant warfare, their immortal love for each other, the death of one and the sacrifice of the other to resurrect him.Tiberius rebuilt the temple of Castor and Pollux, dedicating it in his own name and that of his brother Drusus, who had died in 9 BCE, and associating their names to those of the twin gods as an emotive political statement.
Tiberius also renamed the temple as “Pollux and Castor” – making Pollux the elder brother, clearly seeing himself as this figure. He was proclaiming himself as Pollux the immortal and Drusus as Castor, the dead twin. This is an ironic comparison as it equated Castor, the mortal tamer of horses, with Drusus who died of a fall from his horse. At the same time, Tiberius knew as well as, if not better than, anyone the practical value of the myths of the divine twins to a Roman statesman. The twins were the saviour gods, heralds of military victory, beloved in Rome for five centuries invoked by the people every day. Without his brother Drusus taking the part of Castor, it was entirely possible that Tiberius turned to his son to fill this highly sentimental role by giving him the nickname Castor and keeping him close to the running of the empire although he was not his heir.
Tacitus mentioned Castor and Germanicus together at the beginning of the Annals as the potential heirs of Tiberius, despite the fact that Germanicus’ succession guaranteed at this point and Castor was not considered his heir until Germanicus’ death. The two young men continued to be friendly rivals and Tiberius took pains to ensure that he did not give more power or position to one over the other. However, even without this precaution, Germanicus enjoyed the more important military command granted to him by Augustus and greater popular favor.
That time Castor saved the day
Two mutinies, in Pannonia and Germany began when the troops become restless upon the death of Augustus. Legions became unruly when normal duty was suspended for the period of mourning for Augustus and took the opportunity of the death of the emperor to revolt. The mutiny in Germany, where Germanicus was in charge, had an additional political element to this uprising: these soldiers also hoped that Germanicus might become the new emperor of Rome.

Germanicus hastened to the camp and met with an assemblage of his troops. He ordered them to assemble according to their companies and bring forth their standard before attempting to employ rational argument. However, his men responded by reciting their grievances in detail. They then offered Germanicus supreme power. In response, Germanicus flamboyantly drew his sword and threatened to kill himself. The soldiers were unimpressed – one soldier even offered Germanicus his own sword to use. Germanicus’ gesture was widely considered by scholars as “hysterical”, “desperate” and “ludicrous”.
After this failure, Germanicus forged a letter written in the name of the emperor that offers discharge to twenty-year veterans, released sixteen-year veterans from duty, and asserts that legacies should be doubly paid (Ann. 1.36.3). The letter had the desired effect on the troops and the concessions, unapproved by the emperor, were granted. Germanicus was thus able to temporarily restore order. However, as he granted consessions which were larger than those agreed by Tiberius, he later used his own funds to make up the differences. However, the forged letter lowers some people’s opinion of Germanicus. Tacitus himself comments that the money paid was “stolen” from the treasury (Ann. 1.37.2).
Castor was sent by Tiberius to Pannonia. As with Germanicus, Tiberius sent a letter to his son which says that he could grant only some concessions and the rest must be referred to the senate. Unlike Germanicus, Castor insisted to the soldiers that he could do little without consulting Tiberius. The soldiers angrily shouted abuse at Castor and the situation quickly grew worse. However, an eclipse of the moon frightened the superstitious soldiers as they viewed it as a bad omen, and Castor took this opportunity to play on the soldiers’ misgivings.
By playing upon the soldiers’ fears of the eclipse, Castor manages to turn a chance affair of nature to his advantage. Although he was not a practiced orator, he spoke with natural dignity of a statesman and called an assembly of the soldiers to rebuke them. He compromised by offering to write to Tiberius of their demands without offering additional consessions from himself. He then took further action by having the two leaders of the mutiny, Percennius and Vibulenus, killed. After the mutiny was concluded, Castor returned home without further ceremony to help his father run the empire.