7.  The weakness produced by this division encouraged the enemies of the Romans, whom the dread of Constantine’s power had hitherto kept quiet, to take up arms.  Of these the most formidable was Sa’por king of Persia. 8.  The abilities of Sapor showed that he merited a throne; he had scarcely arrived at maturity when he led an army against Tha’ir king of Arabia, who had harassed Persia during his minority; the expedition was completely successful.  Tha’ir was slain, and the kingdom subdued.  The young conqueror did not abuse his victory; he treated the vanquished with such clemency, that the Arabs gave him the title of Doulacnaf or protector of the nation.

[Sidenote:  A.D. 338.]

9.  On the death of Constantine, Sa’por invaded the eastern provinces of the Roman empire; he was vigorously opposed by Constan’tius, and the war was protracted during several years with varying fortune.  At the battle of Sin’gara, the Romans surprised the Persian camp, but were in their turn driven from it with great slaughter by the troops which Sapor had rallied.  The eldest son of the Persian king was, however, brought off as a prisoner by the Romans, and the barbarous Constan’tius ordered him to be scourged, tortured, and publicly executed. 10.  Though Sa’por had been victorious in the field, he failed in his chief design of seizing the Roman fortresses in Mesopota’mia; during twelve years he repeatedly besieged Ni’sibis, which had been long the great eastern bulwark of the empire, but was invariably baffled by the strength of the place, and the valour of the garrison.  At length both parties became wearied of a struggle which exhausted their resources, and new enemies appearing, they resolved to conclude a peace.  Sa’por returned home to repel an invasion of the Scythians; Constan’tius, by the death of his two brothers, found himself involved in a civil war which required his undivided attention.

11.  Constan’tine had scarcely been seated on his throne, when he attempted to wrest from Con’stans some of the provinces which had been assigned as his portion.  He rashly led his army over the Julian Alps, and devastated the country round Aquile’ia where, falling into an ambuscade, he perished ingloriously.  Con’stans seized on the inheritance of the deceased prince, and retained it during ten years, obstinately refusing to give any share to his brother Constan’tius. 12.  But the tyranny of Con’stans at last became insupportable.  Magnen’tius, an enterprising general, proclaimed himself emperor, and his cause was zealously embraced by the army.  Con’stans was totally unprepared for this insurrection; deserted by all except a few favourites, whom dread of the popular hatred they had justly incurred prevented from desertion, he attempted to escape into Spain, but was overtaken at the foot of the Pyrenees, and murdered. 13.  The prefectures of Gaul and Italy cheerfully submitted to the usurpation of Magnen’tius; but the legions of Illyr’icum elected their general,