Lives of the Necromancers/Gerbert
As a consequence of this state of things the more curious men of
Europe by degrees adopted the practice of resorting to Spain for the purpose of enlarging their sphere of observation and knowledge. Among others Gerbert is reported to have been the first of the Christian clergy, who strung themselves up to the resolution of mixing with the followers of Mahomet, that they might learn from thence things, the knowledge of which it was impossible for them to obtain at home. This generous adventurer, prompted by an insatiable thirst for information, is said to have secretly withdrawn himself from his monastery of Fleury in Burgundy, and to have spent several years among the Saracens of Cordova. Here he acquired a knowledge of the language and learning of the Arabians, particularly of their astronomy, geometry and arithmetic; and he is understood to have been the first that imparted to the north and west of Europe a knowledge of the Arabic numerals, a science, which at first sight might be despised for its simplicity, but which in its consequences is no inconsiderable instrument in subtilising the powers of human intellect. He likewise introduced the use of clocks. He is also represented to have made an extraordinary proficiency in the art of magic; and among other things is said to have constructed a brazen head, which would answer when it was spoken to, and oracularly resolve many difficult questions.  The same historian assures us that Gerbert by the art of necromancy made various discoveries of hidden treasures, and relates in all its circumstances the spectacle of a magic palace he visited underground, with the multiplied splendours of an Arabian tale, but distinguished by this feature, that, though its magnificence was dazzling to the sight, it would not abide the test of feeling, but vanished into air, the moment it was attempted to be touched.
It happened with Gerbert, as with St. Dunstan, that he united an aspiring mind and a boundless spirit of ambition, with the intellectual curiosity which has already been described. The first step that he made into public life and the career for which he panted, consisted in his being named preceptor, first to Robert, king of France, the son of Hugh Capet, and next to Otho the Third, emperor of Germany. Hugh Capet appointed him archbishop of Rheims; but, that dignity being disputed with him, he retired into Germany, and, becoming eminently a favourite with Otho the Third, he was by the influence of that prince raised, first to be archbishop of Ravenna, and afterwards to the papacy by the name of Silvester the Second. 
Cardinal Benno, who was an adherent of the anti-popes, and for that reason is supposed to have calumniated Gerbert and several of his successors, affirms that he was habitually waited on by demons, that by their aid he obtained the papal crown, and that the devil to whom he had sold himself, faithfully promised him that he should live, till he had celebrated high mass at Jerusalem. This however was merely a juggle of the evil spirit; and Gerbert actually died, shortly after having officially dispensed the sacrament at the church of the Holy Cross in Jerusalem, which is one of the seven districts of the city of Rome. This event occurred in the year 1008.