The Year of the Four Emperors, AD 69, was the first civil war of the Roman Empire, during which four emperors ruled in succession: Galba, Otho, Vitellius, and Vespasian. It is considered an important interval, marking the transition from the Julio-Claudians, the first imperial dynasty, to the Flavian dynasty. The period witnessed several rebellions and claimants, with shifting allegiances and widespread turmoil in Rome and the provinces.

In 68, Vindex, legate of Gallia Lugdunensis, revolted against Nero and encouraged Galba, governor of Hispania, to claim the Empire. The latter was acclaimed emperor by his legion in early April. He was notably supported by Otho, legate of Lusitania. Soon after, the legate of a legion in Africa, Clodius Macer, also rebelled against Nero. Vindex was defeated by the Rhine legions at the Battle of Vesontio, but they too rebelled against Nero. Finally, on 9 June 68, Nero committed suicide after having been declared a public enemy by the Senate, which made Galba the new emperor. However, Galba was unable to establish his authority over the Empire, as several of his supporters were disappointed by his lack of gratitude. He especially adopted Piso Licinianus as heir (Galba was childless and elderly), instead of Otho, who, it had widely been assumed, would be chosen. Angered by this disgrace, Otho murdered Galba on 15 January with the help of the Praetorian Guard, and became emperor instead. Unlike Galba he rapidly earned considerable popularity, notably by bestowing favours and emulating Nero's successful early years.

Otho still had to face another claimant, Vitellius, who had been acclaimed by the legions of the Rhine on 1 January 69. Vitellius won the First Battle of Bedriacum on 14 April. Otho committed suicide the next day, and Vitellius was appointed emperor by the Senate on 19 April. The new emperor had little support outside of his veterans from the German legions though. When Vespasian, legate of Syria, made his bid known, he received the allegiance of the legions of the Danube as well as many former supporters of Galba and Otho. After his acclamation in Alexandria on 1 July, Vespasian sent his friend Mucianus with a part of his army to fight Vitellius, but the Danubian legions commanded by Antonius Primus had not waited for Mucianus and defeated Vitellius' legions at the Second Battle of Bedriacum on 24 October. Vitellius was subsequently killed by a mob on 20 December. Mucianus arrived several days after and swiftly secured Vespasian's position in Rome (Primus had acted independently from him).

The death of Vitellius did not end the civil war, as the Rhine legions still rejected the rule of Vespasian and the new Flavian dynasty. Some Batavi provincials led by Civilis had fought them since Vitellius' acclamation. In 70, the new regime finally won the legions' surrender after negotiations, mainly because they lacked an alternative to Vespasian. Later, the new regime distorted the eventsespecially through the writings of the historian Tacitusin order to remove the embarrassment of having relied on the Batavi to fight Roman legions. The Batavi were therefore said to have revolted against Rome, and the events dubbed the Revolt of the Batavi.

Nero ( NEER-oh; full name: Nero Claudius Caesar Augustus Germanicus; 15 December AD 37 – 9 June AD 68) was the fifth Roman emperor and the last emperor of the Julio-Claudian dynasty, reigning from AD 54 until his suicide in 68. He was adopted by the Roman emperor Claudius at the age of 13 and succeeded him to the throne. Nero seems to have been popular with the members of his Praetorian Guard, and with lower-class commoners in Rome and the provinces, but was deeply resented by the Roman aristocracy. Most contemporary sources describe him as tyrannical, self-indulgent and debauched. After being declared a public enemy by the Roman Senate, he committed suicide aged 30.

Nero was born at Antium in AD 37, the son of Gnaeus Domitius Ahenobarbus and Agrippina the Younger, a great-granddaughter of the emperor Augustus. When Nero was two years old, his father died. His mother married the emperor Claudius, who eventually adopted Nero as his heir; when Claudius died in 54, Nero became emperor, with the support firstly of the Praetorian Guard, and then of the Senate. In the early years of his reign Nero was advised and guided by his mother Agrippina, his tutor Seneca the Younger, and his praetorian prefect Sextus Afranius Burrus, but he soon sought to rule independently, and to rid himself of restraining influences. His power struggle with his mother was eventually resolved when he had her murdered. Roman sources also implicate Nero in the deaths of his wife Claudia Octavia – supposedly so that he could marry Poppaea Sabina – and of his foster-brother Britannicus. Most Roman sources present Nero as sexually dissolute. He is said to have "married" a freedman Pythagoras, acting the part of bride at the ceremony. After Poppaea's death in unclear circumstances, Nero in short succession married an aristocratic woman Statilia Messalina and another freedman, Sporus, whom he had castrated.

Nero's practical contributions to Rome's governance focused on diplomacy, trade, and culture. He ordered the construction of amphitheaters, promoted athletic games and contests, and made public appearances as an actor, poet, musician, and charioteer. This scandalised his aristocratic contemporaries as these occupations were usually the domain of slaves, public entertainers and infamous persons. The provision of such entertainments made Nero popular among lower-class citizens, but his performances undermined the Imperial dignity. The costs involved were borne by local elites either directly or through taxation, and were much resented.

During Nero's reign, the general Corbulo fought the Roman–Parthian War of 58–63, and made peace with the hostile Parthian Empire. The Roman general Suetonius Paulinus quashed a major revolt in Britain led by the Iceni's queen Boudica. The Bosporan Kingdom was briefly annexed to the empire, and the First Jewish–Roman War began. When the Roman senator Vindex rebelled, with support from the eventual Roman emperor Galba, Nero was declared a public enemy and condemned to death in absentia. He fled Rome, and on 9 June AD 68 he committed suicide. His death sparked a brief period of civil war known as the Year of the Four Emperors.

Most Roman sources offer overwhelmingly negative assessments of his personality and reign. The historian Tacitus claims the Roman people thought him compulsive and corrupt. Suetonius tells that many Romans believed that the Great Fire of Rome was instigated by Nero to clear land for his planned "Golden House". Tacitus claims that Nero seized Christians as scapegoats for the fire and had them burned alive, seemingly motivated not by public justice but by personal cruelty. Some modern historians question the reliability of the ancient sources on Nero's tyrannical acts, considering his popularity among the Roman commoners. In the eastern provinces of the Empire, a popular legend arose that Nero had not died and would return. After his death, at least three leaders of short-lived, failed rebellions presented themselves as "Nero reborn" in order to gain popular support.