Roman Empire

The Roman Empire ruled the Mediterranean world for nearly five centuries in its Western half and for fifteen centuries in its Eastern half, longer than any state in European history. The conventional date for its founding is 27 BC, when the Senate confirmed Octavian's settlement of the preceding month and granted him the title Augustus. The conventional date for its end is 476 AD, when Odoacer deposed Romulus Augustulus and sent the imperial regalia to Constantinople. In between, more than seventy emperors held the throne — by inheritance, adoption, civil war, and the sword of the Praetorian Guard.

The dynastic history of the imperial Romans is messier than the regnal lists suggest. The Julio-Claudians (27 BC–68 AD) descended from Augustus by adoption and intermarriage but ended with the suicide of Nero in the chaos of the Year of the Four Emperors. The Flavians (69–96) were a single family of provincial Italian origin. The Antonines (96–192) practiced adoptive succession — the Five Good Emperors selected capable adult heirs from outside their bloodlines — until Marcus Aurelius broke with the principle and named his biological son Commodus heir. The Severans (193–235) came from North Africa. The Crisis of the Third Century saw twenty-six emperors in fifty years, most of them murdered by their own troops.

The Empire was refounded by Diocletian (284–305), who divided it into a Tetrarchy of senior and junior emperors and doubled the imperial bureaucracy. Constantine the Great reunited it, converted to Christianity, and founded a new capital at Byzantium in 330. The Theodosian dynasty made Trinitarian Christianity the official religion in 380 and was the last to rule the whole empire before its permanent administrative partition. The Western half collapsed under Germanic pressure in the fifth century; the Eastern half outlived it by a thousand years as the Byzantine Empire.

The Roman dynastic legacy is more thematic than genealogical: the imperial throne descended by adoption, succession, or coup more often than by blood, and the dynasties listed in regnal histories are scholarly conventions rather than self-conscious houses. But the political vocabulary of the imperial Romans — emperor, senate, consul, dictator, tribune — and the legal codifications produced under Theodosius and Justinian shaped European governance until the modern period.