A great civilization is not conquered from without until it has destroyed itself within.
The essential causes of Rome’s decline lay in her people, her morals, her class struggle, her failing trade, her bureaucratic despotism, her stifling taxes, her consuming wars.
A law of Septimius Severus speaks of a penuria hominum—a shortage of men.4 In Greece the depopulation had been going on for centuries. In Alexandria, which had boasted of its numbers, Bishop Dionysius calculated that the population had in his time (250) been halved. He mourned to “see the human race diminishing and constantly wasting away.”
Only the barbarians and the Orientals were increasing, outside the Empire and within.
The holocausts of war and revolution, and perhaps the operation of contraception, abortion, and infanticide, had a dysgenic as well as a numerical effect: the ablest men married latest, bred least, and died soonest. The dole weakened the poor, luxury weakened the rich; and a long peace deprived all classes in the peninsula of the martial qualities and arts. The Germans who were now peopling north Italy and filling the army were physically and morally superior to the surviving native stock; if time had allowed a leisurely assimilation they might have absorbed the classic culture and reinvigorated the Italian blood.
the population of Italy had long since been mingled with Oriental strains physically inferior, though perhaps mentally superior, to the Roman type. The rapidly breeding Germans could not understand the classic culture, did not accept it, did not transmit it; the rapidly breeding Orientals were mostly of a mind to destroy that culture; the Romans, possessing it, sacrificed it to the comforts of sterility.
Rome was conquered not by barbarian invasion from without, but by barbarian multiplication within.
Will Durant 1944
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