by roads, which gave its armies the great advantage of concentrating rapidly on any point that was menaced. Its population was incomparably greater than that of any neighbour; its generals and engineers and the equipment of its troops were unsurpassed in the world; and the emperors of capacity were sufficiently numerous to have atoned for the incompetence of a few. An observer speculating upon manifest destiny, and knowing nothing more of the earth than was known a little earlier to the elder Pliny, might surely have said with reason in Trajan's time, that sooner or later the eagles would certainly fly in triumph over the whole habitable world. Even now, though we can trace the stages of decadence, it is difficult not to be astonished at the completeness of the ruin. Summing up the most obvious causes, we seem to see that the institution of slavery deprived Italy of a large part of her natural and best defenders; that the burden of taxes produced a depopulation in the provinces, as men ceased to marry, or escaped across the border and joined the barbarians; and that while Rome was thus losing her life-blood, Germans and Parthians were acquiring the arts of war, and becoming conscious of their strength. Even so, we have to fall back upon other explanations—upon famines and pestilences that desolated provinces, and upon an upheaval of peoples in the far East, resulting in an exodus of Tartars across Europe—fully to understand why the attack on the Roman Empire became so strong, and was at last so weakly combated.
Optimists are fond of showing that, after all, all happened for the best in the best of all possible worlds.[1] A larger polity, making country life and local institutions possible, supplanted the rule by municipal garri-
