The extraordinary impulse to scientific investigation, to historical research, to the development and perfection of the industrial arts, to the extension of commerce, to the improvement of the social and economic conditions which are so intimately connected with the comfort and happiness of mankind, imparted by the Saracen kingdoms of Southern Europe, was far from being destroyed by the absorption or conquest of their provinces or by the final extinction of their empire. The progress of their humanizing influence upon other nations had been slow and imperceptible. The philosophical ideas and principles advanced by the Arab universities were necessarily hostile to the doctrines of Christianity, to the opinions of the Fathers, to the inspiration of an infallible Pope, to the imperious claims of ecclesiastical supremacy. In consequence of their heretical tendency, they were perused in secret; and the diligence with which this prohibited literature was studied is revealed by the number of sects which arose, and the defiance of Papal authority, which is the distinguishing characteristic of European annals during the first half of the thirteenth century. The doctrines taught at Cordova and Palermo inspired those audacious mediæval reformers, far in advance of their age, whose aspirations for intellectual and religious liberty were promptly and mercilessly extinguished at the stake and on the scaffold. The spirit of resistance to Papal aggression, corruption, and tyranny, temporarily checked, in time revived, and found permanent expression in the bold and revolutionary theories of the Reformation. These great and radical changes were not spontaneously effected; the causes of their development had been in silent operation for many centuries.