The Severan Dynasty includes the increasingly troubled reigns of Septimius Severus (193–211), Caracalla (211–217), Macrinus (217–218), Elagabalus (218–222), and Alexander Severus (222–235). The founder of the dynasty, Lucius Septimius Severus, belonged to a leading native family of Leptis Magna in Africa who allied himself with a prominent Syrian family by his marriage to Julia Domna. Their provincial background and cosmopolitan alliance, eventually giving rise to imperial rulers of Syrian background, Elagabalus and Alexander Severus, testifies to the broad political franchise and economic development of the Roman empire that had been achieved under the Antonines. A generally successful ruler, Septimius Severus cultivated the army's support with substantial remuneration in return for total loyalty to the emperor and substituted equestrian officers for senators in key administrative positions. In this way, he successfully broadened the power base of the imperial administration throughout the empire, also by abolishing the regular standing jury courts of Republican times.

Septimius Severus's son, Marcus Aurelius Antoninus—nicknamed "Caracalla"—removed all legal and political distinction between Italians and provincials, enacting the Constitutio Antoniniana in 212 which extended full Roman citizenship to all free inhabitants of the empire. Caracalla was also responsible for erecting the famous Baths of Caracalla in Rome, their design serving as an architectural model for many subsequent monumental public buildings. Increasingly unstable and autocratic, Caracalla was assassinated by the praetorian prefect Macrinus in 217, who succeeded him briefly as the first emperor not of senatorial rank. The imperial court, however, was dominated by formidable women who arranged the succession of Elagabalus in 218, and Alexander Severus, the last of the dynasty, in 222. In the last phase of the Severan principate, the power of the Senate was somewhat revived and a number of fiscal reforms were enacted. Despite early successes against the Sassanian Empire in the East, Alexander Severus's increasing inability to control the army led eventually to its mutiny and his assassination in 235. The death of Alexander Severus ushered in a subsequent period of soldier-emperors and almost a half-century of civil war and strife. Thus the Pax Romana, which had started at the death of Octavian, ended after about 200 years.