*Lucius Domitius Aurelianus, 270–275 A. D.* Aurelian’s first task was to clear Italy and the Danubian provinces of barbarian invaders. Two incursions of the Alamanni into Raetia and Italy were repulsed, the latter with great slaughter. But the emperor recognized that the security of Italy could no longer be guaranteed and so he ordered the fortification of the Italian cities. The imposing wall which still marks the boundary of part of ancient Rome was begun by Aurelian. A horde of Vandals were beaten and driven out of Pannonia and a victory was won over the Goths in Moesia. But the exposed position of Dacia, and the fact that it was already in large part occupied by the barbarians, induced Aurelian to abandon it altogether. The rest of the Roman settlers were withdrawn to Moesia, where a new province of Dacia was formed behind the barrier of the Danube. *The overthrow of Palmyra.* Aurelian was now ready to attempt his second and greater task, the restoration of imperial unity. And in this the East first claimed his attention. There Vaballathus, the son of Odaenathus, ruled over Palmyra, supported and directed by his mother, Zenobia. At the outset Aurelian had recognized his position but in 271 Vaballathus assumed the title of Augustus and thereby declared his independence of Roman suzerainty. He was able to extend his authority over Egypt and a great part of Asia Minor. In 272 Aurelian set out to bring back the East to its allegiance. He speedily recovered Asia Minor, and entered Syria, where he signally defeated the famous Palmyrene archers and mailed horsemen at Emesa. He then crossed the desert and laid siege to Palmyra itself. Zenobia tried to escape, but was taken, and the city surrendered. The queen and her family were carried off to Rome but Palmyra was at first spared. However, it rebelled again when Aurelian had set out for Rome. Thereupon the emperor returned with all speed and recaptured the city. This time it was utterly destroyed. The authority of Rome was once more firmly reëstablished in the East. *The reconquest of Gaul.* Following his conquest of Palmyra, Aurelian proceeded to overthrow the already tottering empire of the Gauls. At the death of Postumus in 268, Spain and Narbonese Gaul had acknowledged the Roman emperor Claudius Gothicus. After several successors of Postumus had been overthrown by the mutinous Gallic soldiery, Publius Esuvius Tetricus was appointed emperor in Gaul and Britain. However, foreseeing the speedy dissolution of his empire, he secretly entered into negotiations with Aurelian. The latter invaded Gaul and met the Gallic army at the plain of Chalons. In the course of the battle, Tetricus went over to Aurelian, who won a complete victory. Britain and Gaul submitted to the conqueror (274 A. D.). Thus the unity of the empire was restored and Aurelian assumed the title of “Restorer of the World” (_restitutor orbis_).