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268 science had not attained its present importance in the minds of modern nations, and even to this day it is for the most part overlooked by writers of history. The numerous causes under the action of which the Roman Empire was destined to crumble to pieces, and to become the prey of the barbarians, have been again and again set forth with much learning and skill. No doubt the ancient world had grievous internal ills. Slavery, pretorianismprætorianism [sic], corruption of morals, and aversion to matrimony, decay of civic as also of military virtue, the enervation caused by over-refinement, which had exhausted every pleasure and profaned every ideal, and which could not find in itself the means of rising above itself—such are the oft-cited causes to which the inevitable downfall of the Roman domination is ascribed.

And yet the success which almost invariably attended the efforts of vigorous emperors is proof that the state of affairs was not entirely hopeless. Down even to a very late period of the empire's history, the course of events was tolerably amenable to control and regulation, and in the face of the enemy the legions did not altogether belie their hereditary valor and discipline. Even in the palmiest days of the Roman state they had not always been victorious. The introduction of Christianity did not move the ancient world out of the ruts so much as might have been expected. Though a portion of the ancient culture was then thrown overboard, it nevertheless, on the whole, remained intact. There yet stood, under the protection of the victorious cross, temples, theatres, baths, halls of justice; the multitude of the works of art baffled the fury of the destroyers, and the papyrus rolls of the libraries still preserved unscathed the treasures which a thousand years had collected. What was needed was to oppose to the inpouring barbarian hosts from the northeast a barrier which should last until the tide had begun to ebb, and these hordes had themselves come under the influence of civilization: then all would have been well.

It was the opinion of Liebig, who also contemplated the downfall of the ancient culture from the point of view of the natural sciences, that the case was hopeless, whatever might be done. As a result of his researches on mineral manures, Liebig taught that the Roman Empire fell like the Grecian communities at an earlier day, and like the Spanish domination later, because in the countries from which the Romans derived their grain the soil had become exhausted of the mineral matters requisite for growing wheat, especially of phosphoric acid and potash. This doctrine was refuted by Conrad, who shows that the fact of the soil having been exhausted is not proved. In every instance where, according to Liebig, the soil was exhausted by improvident cropping, other reasons may be assigned for the decreased fertility; for instance, drought resulting from the decay of irrigation-works, or from reckless deforestation, and the production of marshes from the want of