The Nerva–Antonine dynasty was a dynasty of 7 Roman Emperors who ruled over the Roman Empire from AD 96 to 192. These Emperors are Nerva, Trajan, Hadrian, Antoninus Pius, Lucius Verus, Marcus Aurelius, and Commodus. The first of these before Commodus (and excluding the co-emperor Lucius Verus) are commonly known as the "Five Good Emperors".
The first five of the six successions within this dynasty were notable in that the reigning Emperor did not have male son, and had to adopt the candidate of his choice to be his successor. Under Roman law, an adoption established a bond legally as strong as that of kinship. Because of this, all but the first and last of the Nerva–Antonine emperors are called Adoptive Emperors.
The importance of official adoption in Roman society has often been considered as a conscious repudiation of the principle of dynastic inheritance and has been deemed one of the factors of the period's prosperity. However, this was not a new practice. It was common for patrician families to adopt, and Roman emperors had adopted heirs in the past: the Emperor Augustus had adopted Tiberius and the Emperor Claudius had adopted Nero. Julius Caesar, dictator perpetuo and considered to be instrumental in the transition from Republic to Empire, adopted Gaius Octavius, who would become Augustus, Rome's first emperor. Moreover, there was a family connection as Trajan adopted his first cousin once removed and great-nephew by marriage Hadrian, and Hadrian made his half-nephew by marriage and heir Antoninus Pius adopt both Hadrian's second cousin three times removed and half-great-nephew by marriage Marcus Aurelius, also Antoninus' nephew by marriage, and the son of his original planned successor, Lucius Verus. The naming of his son Commodus as heir by Marcus Aurelius was considered to be an unfortunate choice and the beginning of the Empire's decline.
With Commodus' murder in 192, the Nerva–Antonine dynasty came to an end; it was followed by a period of turbulence known as the Year of the Five Emperors.
Nerva was the first of the dynasty. Though his reign was short, it saw a partial reconciliation between the army, the senate and the commoners. Nerva adopted as his son the popular military leader Trajan. In turn, Hadrian succeeded Trajan; he had been the latter's heir presumptive and averred that he had been adopted by him on Trajan's deathbed.
In 138, after a long reign dedicated to the cultural unification and consolidation of the empire, the Emperor Hadrian named Antoninus Pius his son and heir, under the condition that he adopt both Marcus Aurelius and Lucius Verus. Hadrian died that same year, and Antoninus began a peaceful, benevolent reign. He adhered strictly to Roman traditions and institutions and shared his power with the Roman Senate.
Marcus Aurelius and Lucius Verus succeeded Antoninus Pius in 161 upon that emperor's death, and co-ruled until Verus' death in 169. Marcus continued the Antonine legacy after Verus' death as an unpretentious and gifted administrator and leader. He died in 180 and was followed by his biological son, Commodus.
The rulers commonly known as the "Five Good Emperors" were Nerva, Trajan, Hadrian, Antoninus Pius, and Marcus Aurelius. The term was coined by Niccolò Machiavelli in his posthumously published book The Discourses on Livy from 1531:
From the study of this history we may also learn how a good government is to be established; for while all the emperors who succeeded to the throne by birth, except Titus, were bad, all were good who succeeded by adoption, as in the case of the five from Nerva to Marcus. But as soon as the empire fell once more to the heirs by birth, its ruin recommenced.
Machiavelli argued that these adopted emperors earned the respect of those around them through good governing:
Titus, Nerva, Trajan, Hadrian, Antoninus, and Marcus had no need of praetorian cohorts, or of countless legions to guard them, but were defended by their own good lives, the good-will of their subjects, and the attachment of the senate.
Edward Gibbon wrote in that their rule was a time when "the Roman Empire was governed by absolute power, under the guidance of wisdom and virtue". Gibbon believed that these benevolent monarchs and their moderate policies were unusual and contrasted with their more tyrannical and oppressive successors.
One hypothesis posits that adoptive succession is thought to have arisen because of a lack of biological heirs. All but the last of the adoptive emperors had no legitimate biological sons to succeed them. They were therefore obliged to pick a successor somewhere else; as soon as the Emperor could look towards a biological son to succeed him, adoptive succession was set aside.