of Mesopotamia recovered, but the entire tract between the rivers as far south as the latitude of Bagdad was ravaged, and even the two great cities of Seleucia and Ctesiphon were taken without the slightest difficulty.  Persia Proper seemed to lie open to the invader, and Carus was preparing to penetrate still further to the east, when again an opportune death checked the progress of the Roman arms, and perhaps saved the Persian monarchy from destruction.  Carus had announced his intention of continuing his march; some discontent had shown itself; and an oracle had been quoted which declared that a Roman emperor would never proceed victoriously beyond Ctesiphon, Carus was not convinced, but he fell sick, and his projects were delayed; he was still in his camp near Ctesiphon, when a terrible thunderstorm broke over the ground occupied by the Roman army.  A weird darkness was spread around, amid which flash followed flash at brief intervals, and peal upon peal terrified the superstitious soldiery.  Suddenly, after the most violent clap of all, the cry arose that the Emperor was dead.  Some said that his tent had been struck by lightning, and that his death was owing to this cause; others believed that he had simply happened to succumb to his malady at the exact moment of the last thunder-clap; a third theory was that his attendants had taken advantage of the general confusion to assassinate him, and that he merely added another to the long list of Roman emperors murdered by those who hoped to profit by their removal.  It is not likely that the problem of what really caused the death of Carus will ever be solved.  That he died very late in A.D. 283, or within the first fortnight of A.D. 284, is certain; and it is no less certain that his death was most fortunate for Persia, since it brought the war to an end when it had reached a point at which any further reverses would have been disastrous, and gave the Persians a breathing-space during which they might, at least partially, recover from their prostration.

Upon the death of Carus, the Romans at once determined on retreat.  It was generally believed that the imperial tent had been struck by lightning; and it was concluded that the decision of the gods against the further advance of the invading army had been thereby unmistakably declared.  The army considered that it had done enough, and was anxious to return home; the feeble successor of Carus, his son Numerian, if he possessed the will, was at any rate without the power to resist the wishes of the troops; and the result was that the legions quitted the East without further fighting, and without securing, by the conclusion of formal terms of peace, any permanent advantage from their victories.