Of the Moslem civilisation as a whole, it must be said that on the material side, in Spain and the East, it was such a success as had not been attained under the Romans previously (though it was exceeded in Egypt by the Lagids), and has not been reached in Christian Spain since the fall of Boabdil. Economically, the Moorish regimen was sound and stable in comparison with that of imperial Spain, which, like Rome, merely set up a factitious civilisation on the basis of imported bullion and provincial tribute, and decayed industrially while nominally growing in empire and power. When the history of Spain from the seventeenth century onward is compared with that of the Saracens up to their overthrow, the nullity of explanations in terms of race qualities becomes sufficiently plain--unless, indeed, it is argued that Moorish blood is the secret of Spanish decadence. But that surmise too is folly. Spanish decadence is a perfectly simple sociological sequence;[395] and a Spanish renascence is not only conceivable, but likely, under conditions of free science and free thought. Nor is it on the whole less likely that the Arab stock will in time to come contribute afresh and largely to civilisation. The one element which can finally distinguish one race from another--acquired physiological adaptation to a given climate--marks the Arab races as best fitted for the recovery of great southern and eastern regions which, once enormously productive, have since the fall of the Roman and Byzantine Empires been reduced to sterility and poverty. The Greeks in their recovered fatherland, and the French in Algeria, have not thus far been much more successful than the Turks in developing material prosperity. If North Africa, Syria, and Mesopotamia are again to be rich and fruitful lands, it must be in the hands of an acclimatised race; and the Arab stocks are in this regard among the most eligible.