It is necessary to begin a history of the middle ages with reference to the decline of the Roman Empire. This decline was caused by various circumstances, but chiefly by the weakened condition of society. Instead of rearing a respectable lower and middle class, the Roman aristocracy kept the mass of the people in slavery, so that at length society consisted of but a comparatively small number of privileged persons, including the military, and vast numbers of serfs or slaves――the hangers-on of great men――and in effect paupers. ‘The freedom of the ancient world expired in the course of ages,’ says Alison, ‘from the small number of those who enjoyed its benefits. The ruling citizens became corrupted from the influence of prosperity, or by the seduction of wealth; and no infusion of energy took place from the lower ranks to renovate their strength or supply their place.’ Besides this general, there was a special cause. In 321, Constantine transferred the imperial abode from Rome to Byzantium, a city situated on the Bosphorus, and afterwards called Constantinople. In his endeavors to make this city the seat of government, Constantine only partially succeeded; for it generally happened after his day that there was one emperor in the East and another in the West, and not unfrequently two or three different individuals in the provinces, at the head of considerable military forces, claiming partial and even universal empire. Rome itself, and the countries of western Europe, were soon taken posession of by barbarous intruders, and lost all the characteristics and individuality of empire; but Constantinople continued for a thousand years the abode of men who had still the name of emperors, reckoning themselves the descendants of the Cæsars, although they had long ceased to wield anything but the shadow of power. Constantine was himself instrumental in dismembering his empire, having before his death divided it among no fewer than five individuals――namely, his three sons, Constantine, Constans, Constantius, and his two nephews, Dalmatius and Annipalianus, both of whom bore in addition the surname of Cæsar――a name still popular among a people who wished themselves to be considered Roman.