What Was the Julio-Claudian Era?:

Ancient Roman history is divided into 3 periods:

1. Regal,
2. Republican, and
3. Imperial

Sometimes there's an additional (4)Byzantine Period.
The Imperial period is the time of the Roman Empire.

The 1st leader of the Imperial period was Augustus, who was from the Julian family of Rome. The next four emperors were all from his or his wife's (Claudian) family. The two family names are combined in the form Julio-Claudian.

The Julio-Claudian era covers the first few Roman emperors, Augustus, Tiberius, Caligula, Claudius, and Nero.

Succession:

Since the Roman Empire was new at the time of the Julio-Claudians, it still had to work out issues of succession. The first emperor, Augustus, made much of the fact that he was still following the rules of the Republic, which permitted dictators. Rome hated kings, so although emperors were kings in all but name, direct reference to succession of the kings would have been anathema. Instead, the Romans had to work out the rules of succession as they went.

They had models, like the aristocratic road to political office (cursus honorum), and, at least in the beginning, expected emperors to have illustrious ancestors. It soon became apparent that a potential emperor's claim to the throne required money and military backing.

Augustus:

The senatorial class historically passed along their status to their offspring, so succession within a family was acceptable; however, Augustus lacked a son to whom to pass along his privileges.

In 23 B.C., when he thought he would die, Augustus handed a ring conveying imperial power to his trusted friend and general Agrippa. Augustus recovered. Family circumstances changed. Augustus adopted Tiberius, his wife's son, in A.D. 4 and gave him proconsular and tribunician power. He married his heir to his daughter Julia. In 13, Augustus made Tiberius co-regent. When Augustus died, Tiberius already had imperial power.

Conflicts could be minimized if the successor had had the opportunity to co-rule.

Tiberius:

Following Augustus, the next four emperors of Rome were all related to Augustus or his wife Livia. They are referred to as Julio-Claudians. Augustus had been very popular and so Rome felt allegiance to his descendants, too.

Tiberius, who had been married to Augustus' daughter and was the son of Augustus' third wife Julia, had not yet openly decided who would follow him when he died in A.D. 37. There were 2 possibilities: Tiberius' grandson Tiberius Gemellus or the son of Germanicus. (On Augustus' order, Tiberius had adopted Augustus' nephew Germanicus.) Tiberius named them equal heirs.

Caligula (Gaius):

The PraetorianPrefect Macro supported Caligula (Gaius) and the Senate of Rome accepted the prefect's candidate. The young emperor seemed promising at first but soon suffered a serious illness from which he emerged a terror. Caligula demanded extreme honors be paid to him and otherwise humiliated the Senate. He alienated the praetorians who killed him after 4 years as emperor. Unsurprisingly, Caligula had not yet selected a successor.

Claudius:

Praetorians found Claudius cowering behind a curtain after they assassinated his nephew Caligula. They were in the process of ransacking the palace, but instead of killing Claudius, they recognized him as the brother of their much loved Germanicus and persuaded Claudius to take the throne. The Senate had been at work finding a new successor, too, but the praetorians, again, imposed their will.

The new emperor bought the continued allegiance the praetorian guard.

One of Claudius' wives, Messalina, had produced an heir known as Britannicus, but Claudius' last wife, Agrippina, persuaded Claudius to adopt her son, whom we know as Nero. as heir.

Nero:

Claudius died before the full inheritance had been accomplished, but Agrippina had support for her son, Nero, from the Praetorian Prefect Burrus whose troops were assured a financial bounty. The Senate again confirmed the praetorian's choice of successor and so Nero became the last of the Julio-Claudian emperors.

Later Successions:

Later emperors often designated successors or co-regents. They could also bestow the title of "caesar" on their sons or other family member. When there was a gap in the dynastic rule, the new emperor had to be proclaimed either by the Senate or the army, but the consent of the other was required to make the succession legitimate. The emperor also had to be acclaimed by the people.

Women were potential successors, but the first woman to rule in her own name, Empress Irene (c. 752 - August 9, 803), and alone, was after our time period.

Succession Problems:

The first century saw 13 emperors, the 2nd, 9, but then the 3rd produced 37 (plus the 50 Michael Burger says never made it to the rolls of the historians). Generals would march on Rome where the terrified senate would declare them emperor (imperator, princeps, and augustus). Many of these emperors with nothing more than force legitimating their positions, had assassination to look forward to.

Sources: A History of Rome, by M. Cary and H.H. Scullard. 1980.
Also J.B. Bury's History of the Later Roman Empire and The Shaping of Western Civilization: From Antiquity to the Enlightenment, by Michael Burger.

For more information on imperial succession, see: "The Transmission of the Powers of the Roman Emperor from the Death of Nero in A.D. 68 to That of Alexander Severus in A.D. 235," by Mason Hammond; Memoirs of the American Academy in Rome, Vol. 24, (1956), pp. 61+63-133.