The great Saracen invasion was at hand, and it was at the very moment of Heraclius’ triumph that Mahomet sent out his famous circular letter to the kings of the earth, inviting them to embrace Islam. If the Emperor could but have known that his desolated realm, spoiled for ten long years by the Persian and the Avar, and drained of men and money, was to be invaded by a new enemy far more terrible than the old, he would have prayed that the day of his triumph might also be the day of his death. XI. SOCIAL AND RELIGIOUS LIFE. (A.D. 320-620.) The reign of Heraclius forms the best dividing point in the history of the empire between what may roughly be called Ancient History and the Middle Ages. There is no break at all between Constantine and Heraclius, though the area, character, social life, and religion of the empire had been greatly modified in the three hundred years that separated them. The new order of things, which commenced when Constantine established his capital on the Bosphorus, had a peaceable and orderly development. The first prominent fact that strikes the eye in the history of the three centuries is that the sceptre passed from sovereign to sovereign in quiet and undisturbed devolution. From the death of Valens onward there is no instance of a military usurper breaking the line of succession till the crowning of Phocas in 602. The emperors were either designated by their predecessors or—less frequently—chosen by the high officials and the senate. The regularity of their sequence is all the more astonishing when we realize that only in three cases in the whole period was father succeeded by son. Saving Constantine himself, Theodosius I., and Arcadius, not a single emperor left male issue; yet the hereditary instinct had grown so strong in the empire that nephews, sons-in-law, and brothers-in-law of sovereigns were gladly received as their legitimate heirs. Considering this tendency, it is extraordinary to note that the whole three hundred years did not produce a single unmitigated tyrant. Constantius II. was gloomy and sometimes cruel, Valens was stupid and avaricious, Arcadius utterly weak and inept, Justinian hard and thankless; but the general average of the emperors were men of respectable ability, and in moral character they will compare favourably with any list of sovereigns of similar length that any country can produce.