With the establishment of the Empire, the antagonism between Rome and Persia became still more strongly marked, and a struggle commenced which lasted with little intermission until the foundation of the Mahommedan Caliphate. In this struggle the advantage was not always, as we should like to think, on the side of the Europeans. While Augustus reigns, Horace boasts, there is no occasion to dread the “dreadful Parthians[773]”; but Corbulo is perpetually fighting them, and when Nero commits suicide, the legend immediately springs up that the tyrant is not dead, but has only betaken himself beyond the Euphrates to return with an army of Rome’s most dreaded enemies to lay waste his rebellious country[774]. Towards the close of the first Christian century, Trajan, fired, according to Gibbon, by the example of Alexander, led an army into the East and achieved successes which enabled him to add to his titles that of Parthicus[775]; but the whole of his Oriental conquests were given back by the prudent Hadrian on his succession to the throne. During the reign of Marcus Aurelius, Avidius Cassius obtained some solid victories on the frontier; but Macrinus is said to have bought off the Parthians with a bribe of nearly two millions of money. The rise of the Sassanian house and the retransfer of the leadership from the Parthians to their kinsmen in Persia proper brought about the reform of the Persian religion, and added another impulse to the increasing strength of Persian national feeling. Alexander Severus may have gained some successes in the field over Ardeshîr or Artaxerxes, the restorer of the Persian monarchy[776]; but in the reign of the last named king’s son and successor Sapor, the capture of the Emperor Valerian with his whole army, and the subsequent ravaging of the Roman provinces in Asia by the victors, showed the Republic how terrible was the might of the restored kingdom[777]. Aurelian, the conqueror of Palmyra, did much to restore the prestige of Roman arms in the East; and although he was assassinated when on the march against Persia, the Emperor Carus shortly after led a successful expedition into the heart of the Persian kingdom[778]. In the reign of Diocletian, indeed, the Persians lost five provinces to the Romans[779]; but under Constantine the Great the Romans were again vanquished in the field, and the Persians were only prevented by the heroic resistance of the fortified town of Nisibis and an incursion into their Eastern provinces of tribes from Central Asia from again overrunning the Asiatic possessions of Rome[780].