The southern route, reaching Europe through Egypt, was mainly maritime. It had to contend with two great difficulties: the great stretch of open water presented by the Indian Ocean, and the difficulty of navigation in the Red Sea, on the west coast of which strong north winds blow through much of the year. The first of these difficulties became less serious in the Christian era, as navigators learned to time their voyages to suit the monsoons, the winds blowing at regular seasons in the Indian Ocean. Vessels could leave an Egyptian port in July and reach India by the southwest monsoon in little over two months. The second difficulty was obviated by starting for the East not from the Gulf of Suez but from a point part way down the coast (Berenice), reached by a trip on the Nile and by caravan. This route became of greatest importance at the close of the Middle Ages. The third route, entirely overland, led from India across the mountains to the River Oxus, where it was joined by a caravan route from China. Branching near Bokhara, one part led to the Caspian Sea and up the Volga, another left the Caspian to the north and reached Europe at the Black Sea (Trebizond, Constantinople). This route traversed high mountain passes and long desert stretches, and was suitable only for the carriage of valuable articles of small bulk. For about two centuries after 1250 it was kept open by the Mongols or Tartars, who lived on good terms with the Christians; then it was blocked by the Turks. =97. Character of the crusades; number of crusaders.=—To assign to economic motives the chief part in the crusades would be a distortion of the great movement which marked the life of Europe in the two centuries following 1100. Not hope of gain but vague ideals of this life and the life to come drove hundreds of thousands of men to the perilous journey to the Holy Land from which so few returned. Indirectly commerce had its share in this movement; it had drawn the peoples closer together, stimulated curiosity and broadened interests. Men sought an outlet for their surplus energy, and a relief from the monotony of medieval life; ascetic ideals imposed upon them holy tasks which they could fulfil to the benefit of their souls. The effect can be traced in an increase in the pilgrimages of individuals to holy places. The people of Europe needed only organization and a leader to unite their scattered forces; they found their organization in the church, their leader in the Pope and his delegates, their goal in the delivery of the Holy Sepulcher from the hands of the infidels who were abusing Christian pilgrims.