In order to understand properly the working of the prohibition of interest and its relation to manumission, it is necessary to carry the analysis one step farther to its ultimate physical basis, which was the conditioning factor of actual practice and eventually of theory also. The exhaustion of the soil of western Europe which was the result of ancient methods of agriculture, together with the rising standard of living and the competition of other more fertile agricultural regions like Egypt and North Africa resulted in the substitution of the latifundi for small landholdings.[27] As the pressure continued the latifundi in turn became economically unprofitable under forced labor (slavery) and large tracts of land were abandoned. In order to put this land under agriculture again the charge upon it had to be reduced by the substitution of (relatively) free associated labor, villeinage or serfdom. But this change cut off the economic margin upon which the structure of ancient civilization was built and is the ultimate economic reason assignable for the fall of Rome. Of course the collapse of the empire could, theoretically, have been avoided had the Romans of the first three centuries A.D. been content to live the toilsome and frugal life of the Romans of the early republic. But this was an utter impossibility in practice. This slowly working and hardly understood decline in the relative and actual ability of ancient agriculture to sustain the weight imposed upon it, enables us to see why the sinfulness of interest could be steadily indoctrined even though steadily evaded, by Christians from the beginning, while manumission was not taught at all in the beginning and only worked up to the dignity of a pious action relatively late.[28] It also explains why manumission of household and personal slaves preceded that of agricultural slaves. Of course there is nothing peculiarly Christian about this later phenomenon and the operation of other causes is discernable, but it is important for our purpose to observe that Christian practice, and Christian theory in property matters in the long run, followed the broad lines of the underlying economic evolution.[29] The application of this to the origin of Christian monasticism and to the revival of communistic theories by the later Church fathers lies at the very outside limit of our study but will be briefly touched on after we have considered the final overthrow of the communistic property concept as they appear in the earlier fathers up to and including Tertullian.