Marcus Agrippa Postumus (12 BC – August 14 AD), later named Agrippa Julius Caesar, was a grandson of Roman Emperor Augustus. He was the youngest child of Marcus Vipsanius Agrippa and Julia the Elder. Augustus initially considered Postumus as a potential successor and formally adopted him as his heir, before banishing Postumus from Rome in AD 6 on account of his ferocia ("beastly nature"). In effect, though not in law, the action cancelled his adoption and virtually assured Tiberius' emplacement as Augustus' sole heir. Postumus was ultimately executed by his own guards shortly after Augustus' death in AD 14.
Postumus was a member of the Julio-Claudian dynasty, the first imperial family of the Roman Empire. His maternal grandparents were Augustus and his second wife, Scribonia. Postumus was also a maternal uncle of Emperor Caligula, who was the son of Postumus' sister Agrippina the Elder, as well as a great-uncle of Nero, the last Julio-Claudian emperor, whose mother, Agrippina the Younger, was Caligula's sister.
Postumus was initially named "Marcus Agrippa" in honour of his father, who died shortly before his birth and so the surname Postumus was added. After the death of his older brothers, Lucius and Gaius Caesar, Postumus was adopted by his maternal grandfather, Augustus. A lex curiata ratified his adoption from which Postumus assumed the filiation Augusti f., meaning "son of Augustus". Postumus was then legally the son of Augustus, as well as his biological grandson. As a consequence, Postumus was adopted into the Julia gens and took the name "Julius Caesar". His name was changed to Agrippa Julius Caesar.
Agrippa Postumus was born in Rome in 12 BC, approximately three months after his father, Marcus Vipsanius Agrippa, had died in the summer. He was born into the equestrian gens Vipsania. His father was one of Augustus' leading generals and his mother, Julia the Elder, was the daughter of Augustus and his second wife, Scribonia. Postumus was the third son and last child of Agrippa and Julia; his older siblings were Gaius Caesar, Julia the Younger, Lucius Caesar and Agrippina the Elder. Both of his brothers, Gaius and Lucius, were adopted by Augustus after the birth of Lucius in 17 BC.
Before Gaius left Rome for Asia, Gaius and Lucius had been given the authority to consecrate the Temple of Mars Ultor (1 August 2 BC), and they managed the games that were held to celebrate the dedication of the Temple. Postumus, still a student, participated in the Lusus Troiae ("Trojan Games") with the rest of the equestrian youth. At these games, according to Cassius Dio, 260 lions were slaughtered in the Circus Maximus, there was gladiatorial combat and a naval battle between the "Persians" and the "Athenians" and 36 crocodiles were slaughtered in the Circus Flaminius.
At first Augustus opted not to adopt Postumus so that Agrippa would have at least one son to carry on his family name. However the untimely deaths of principes Lucius (d. AD 2) and Gaius (d. AD 4) forced Augustus to adopt Postumus, his only remaining biological grandson, and Tiberius, Augustus' eldest stepson from his third wife, Livia, on 26 June AD 4 to secure the succession. He agreed to adopt Tiberius if Tiberius first adopted Germanicus. Upon his adoption into the Julii Caesares, Postumus assumed the name Marcus Julius Caesar Agrippa Postumus. After the adoptions of AD 4, in the event of Augustus' death the title of princeps would pass first to Tiberius and then to Germanicus.
It was not intended that Postumus receive the emperorship; instead he was meant to be the heir to Augustus' bloodline. He would receive Augustus' name, property and bloodline but not the title of princeps. Indeed, Postumus was not given any special schooling or treatment after his adoption. In AD 5, at the age of 17, he received the toga virilis and his name was added to the list of aristocratic youth eligible for training as military officers. That differed greatly from the honours received by his brothers, both of whom were inducted into the Roman Forum by Augustus himself to commemorate their adoptions, given the title Princeps Iuventutis ("Leader of the Youth") and promised the consulship five years in advance, to be held when they reached 19.
In AD 6, an uprising began in the Roman province of Illyricum. Augustus sent Tiberius to crush the revolt with his army, and after a year of delayed results, he sent Germanicus in his capacity as quaestor to assist in bringing the war to a swift end. The reason, Dio says, that Germanicus was chosen over Postumus is because Postumus was of an "illiberal nature".
Postumus was known for being brutish, insolent, stubborn and potentially violent. He possessed great physical strength and reportedly showed little interest in anything other than fishing. He resisted all efforts to improve his behavior, which forced Augustus to "abdicate" him from the Julii in AD 6 and banish him to a villa at Surrentum, near Pompeii. As an abdicated adoptee (adoptatus abdicatus), he lost the Julian name and returned to the gens Vipsania. The ancient historian Velleius Paterculus had this to say of the banishment:
The following year, in 7 AD, Augustus had the Senate make Postumus' banishment permanent and had him moved to Planasia (now Pianosa, Italy), a small island between Italy and Corsica. Augustus bolstered the natural inaccessibility of the rocky island by having an armed guard installed there. The Senate was ordered never to allow his release.
No consensus has emerged as to why Augustus banished Postumus. Tacitus suggests that Augustus' wife, Livia, had always disliked and shunned Postumus, as he stood in the way of her son, Tiberius, succeeding to power after Augustus since Postumus was a direct biological descendant of Augustus, unlike Tiberius. Some modern historians theorise that Postumus may have become involved in a conspiracy against Augustus. Postumus was held under intense security.
Postumus' sister Julia was banished around the same time (AD 8), and her husband, Lucius Aemilius Paullus, was executed for allegedly plotting a conspiracy against Augustus. There was later a conspiracy to rescue Julia and Postumus by Lucius Audasius and Asinius Epicadus. Audasius was an accused forger of advanced age and Asinius was half-Illyrian. According to Suetonius, Audasius and Epicadus had planned to take Julia and Postumus by force to the armies. It is unclear what their exact plan was or even to which armies Suetonius was referring because the conspiracy was discovered early in its planning, possibly before they had even left Rome.
Augustus made no effort to contact Postumus until AD 14. In the summer of that year Augustus left Rome, never to see the capital again. The main ancient sources of information about the period, Tacitus and Cassius Dio, suggest that Augustus left Rome in the company of only one trusted friend, the senator Paullus Fabius Maximus. They left for Planasia to pay Augustus' banished grandson a highly controversial visit.
Fabius and then Augustus died on their return without revealing what they had been doing. Tacitus reports their visit to Planasia as a rumour although Dio reports it as fact. According to the historian Robin Lane Fox, the alleged visit has sometimes been dismissed by modern scholars. However it has been shown that Augustus and Fabius were absent from Rome in mid-May of AD 14. Augustus' adopted grandson, Drusus the Younger, was then being admitted into the Arval Brethren, and an inscription (ILS, 5026) shows that both Augustus and Fabius voted in absentia to admit him into the priesthood.
There was much gossip over the outcome of their expedition. Tacitus recounts the rumour that Augustus had decided to reverse his decision and make Postumus his successor. In his account Fabius indiscreetly told his wife what had occurred during the trip, and that cost him his life. Augustus' wife, Livia, too was said to have poisoned her husband to prevent Postumus from becoming the successor and thus supplanting her son, Tiberius. While modern historians, including Fox, agree that such stories are highly unlikely, there is evidence that Augustus' journey was historical. "It is the last act in Augustus' long marathon of finding and keeping an heir to the new Empire."