Lucius Septimius Severus' political actions took center stage after the civil war of 193-197, with the elimination of his rivals and the transformation of the Roman emperor from a protector of the government on behalf of the Senate to the master of the state on behalf of the Army. The concept of princeps was replaced by that of dominus.

The first dynast of the Severan dynasty married the noble Syrian Julia Domna, introducing a Middle Eastern vision of power that was more closely tied to religion and dynastic rights. During this period, coinage began depicting the emperor with divine attributes, such as a solar crown. After Severus' death in 211, Julia Domna and her circle of Syrian princesses became the true holders of power. She strengthened her eldest son, Caracalla, against his younger brother, Geta, who was assassinated less than a year after their father's death. When the praetorian prefect Macrinus killed Caracalla in 217, it was once again Julia who passed off her sister's nephew as Caracalla's son, securing his rise to power against Macrinus, who was defeated by his supporters near Antioch the following year.

In 218, Rome thus had a fourteen-year-old priest of the solar cult from Emesa as emperor: Sextus Varius Avitus Bassianus, better known as Elagabalus. His nickname came from the Arab deity he worshiped: El-Gabal. The new emperor introduced this deity to Rome, identifying it with Sol Invictus and transforming the public religion into a form of henotheism. The accounts of his reign come from his opponents and are full of gossip, but the fervor with which he sought to center Roman religious life around himself and his god was uncompromising and deeply offensive to the conservative senatorial class. He seemed unaware that he was living in a volatile time when a group of rebellious soldiers could easily attempt to elevate their own leader through violence. In 222, Elagabalus was assassinated by the Praetorians, and his cousin Alexander succeeded him, only to meet the same fate in 235. From then on, for about fifty years, the Empire would descend into military anarchy.