The Mohammedans, in the centuries of their life in Spain, had developed an elegant and prosperous civilization. By means of irrigation and skillful planting, they had converted southern Spain into a garden. They were the most skillful agriculturists and breeders of horses and sheep in Europe, and they carried to perfection many fine arts, while knowledge and learning were nowhere further advanced than here. Through contact with this remarkable people the Christian Spaniards gained much. Unfortunately, however, the spirit of religious intolerance was so strong, and the hatred engendered by the centuries of religious war was so violent, that in the end the Spaniard became imbued with so fierce a fanaticism that he has ever since appeared unable properly to appreciate or justly to treat any who differed from him in religious belief. The Conquests of the Mohammedans.--In the fifteenth century, religious toleration was but little known in the world, and the people of the great Mohammedan faith still threatened to overwhelm Christian Europe. Since the first great conquests of Islam in the eighth century had been repulsed from central Europe, that faith had shown a wonderful power of winning its way. In the tenth century Asia Minor was invaded by hordes of Seljuks, or Turks, who poured down from central Asia in conquering bands. These tribes had overthrown the Arab's power in Mesopotamia and Asia Minor only to become converts to his faith. With freshened zeal they hurled themselves upon the old Christian empire, which at Constantinople had survived the fall of the rest of the Roman world. The Crusades.--The Seljuk Turks had conquered most of Asia Minor, Syria, and the Holy Land. A great fear came over the people of Europe that the city of Constantinople would be captured and they, too, be overwhelmed by these new Mohammedan enemies. The passionate religious zeal of the Middle Age also roused the princes and knights of Europe to try to wrest from the infidel the Holy Land of Palestine, where were the birthplace of Christianity and the site of the Sepulcher of Christ. Palestine was recovered and Christian states were established there, which lasted for over a hundred and eighty years. Then the Arab power revived and, operating from Egypt, finally retook Jerusalem and expelled the Christian from the Holy Land, to which he has never yet returned as a conqueror.