Islamic philosophic thought presents a greater diversity than medieval Christian philosophy. Many of the translators who were employed in the incomparably more numerous translations undertaken in the Muslim period were Syriac-speaking Christians, who used in the novel task the traditional technique worked out in turning Greek texts into their native language which, being Semitic, has a certain affinity with Arabic. Al-Kindi, who was the author of numerous medical works, seems to have rejected alchemy, but believed in astrology, and composed a certain number of writings dealing with questions pertaining to this science. Al-Farabi, 'the Second Teacher' after Aristotle, was considered as the greatest Muslim philosopher up to the advent of Ibn Sina, who was decisively influenced by him. Ibn Sina was a native of Bukhara and familiar with both Persian and Arabic. At the end of the fifth/eleventh century, Muslim Spain was annexed by the fanatical Almoravids, whose armies came over from Africa and defeated the Christians in 479/1086.