Early life and family
He was born in 14 BC in Rome with the name Nero Claudius Drusus, and is often referred to by historians as Drusus II, Drusus the Younger and Drusus Minor to distinguish him from his paternal uncle, Nero Claudius Drusus, the younger brother of Tiberius after whom Drusus was named. Drusus was the maternal grandson of Marcus Vipsanius Agrippa, a close friend of Augustus, and his first wife Caecilia Attica.
As a member of the Julio-Claudian dynasty, he was a close relative of all five Julio-Claudian emperors. His father was emperor, and his adoptive grandfather was the founder of the Roman Empire, Augustus. On his mother's side, he was the cousin of Caligula, a paternal cousin of Claudius, and a first cousin once removed of Nero - all future emperors of Rome.
Before Tiberius, the heirs of Augustus were the sons of Marcus Agrippa, Gaius and Lucius Caesar, whom he adopted and made heir. They advanced through their careers at the same pace and were going to rule together; however, they died young, forcing Augustus to draw another line of succession. In AD 4, Augustus adopted Tiberius on condition that Tiberius adopt Germanicus. This made Tiberius the heir of Augustus, and Germanicus the heir of Tiberius. Like the sons of Agrippa, it was the intention of Augustus that Germanicus and Drusus would rule together.[note 1]
Later that year, Drusus was married to his paternal cousin, Livilla, to bring him closer to the Julians. Tacitus says she was unattractive as a child, but grew up to be beautiful. Their daughter Julia was born not long after the marriage, and they had twin sons: Tiberius Gemellus and Tiberius Claudius Caesar Germanicus II Gemellus in 19, the latter of whom died while still an infant in 23. The birth of his sons was commemorated on coins.
Just as Agrippa's sons were, Drusus was about the same age as Germanicus, and both of them also followed parallel careers. Drusus and Germanicus held all their offices at the same age, and progressed through the cursus honorum at the same pace. Both held the office of quaestor at the same age, both were exempted from holding the praetorship, they held their first and second consulships at the same age, and both were given proconsular imperium maius when they were sent to govern Germania and Illyricum respectively.