Aurelian, Latin in full Lucius Domitius Aurelianus, (born c. 215—died 275, near Byzantium [now Istanbul, Turkey]), Roman emperor from 270 to 275. By reuniting the empire, which had virtually disintegrated under the pressure of invasions and internal revolts, he earned his self-adopted title restitutor orbis (“restorer of the world”).

Aurelian, born near the Danube River, had established himself as an army officer when, about 260, from outside pressure and internal fragmentation of authority, the frontiers of the empire suddenly collapsed. With his compatriot Claudius, Aurelian led the cavalry of the emperor Gallienus (253–268), and, upon Gallienus’s assassination in 268, Claudius became emperor. The new ruler quickly suppressed the rebellion of the usurper Aureolus, but, after a reign of 18 months, Claudius died. His brother Quintillus, who ruled about three months, died or was killed, and in September 270 Aurelian succeeded as emperor.

Aurelian quickly set about restoring Roman authority in Europe. He turned back the Vandals from Pannonia (in present-day central Europe) and after a series of battles expelled the Alemanni and Juthungi from northern Italy and chased the Juthungi across the Danube. Returning to Rome, he quelled a revolt at the imperial mint. For protection against tribal incursions, the emperor ordered the construction of a new city wall around Rome, much of which still stands and still bears his name.