Nothing shows the great influence of the Church so much as the Crusades. The followers of Mohammed had captured Jerusalem (637). Four and a half centuries later, the Holy City was captured by Muslim Turks (1076), and they ill-treated Christian pilgrims. Peter the Hermit and Urban the Pope then roused all Christian Europe against them. In a sermon at Clermont (1095) in France, Urban thus addressed the crowd:
"Oh, race of Franks, set apart from all other nations by your Catholic faith and the honour which you render to the Holy Church, to you our discourse is addressed. From the confines of Jerusalem and from the city of Constantinople a grievous report has repeatedly been brought to our ears -- namely, that an accursed race has violently invaded the lands of the Christians with pillage and fire. They have either destroyed the churches of God or used them for the rites of their own religion.
"Let the deeds of your ancestors encourage you: the glory and greatness of King Charlemagne and your other monarchs, who have extended the sway of the Holy Church over lands previously pagan. Let the Holy Sepulchre of our Lord and Saviour, which is possessed by the unclean nations, arouse you. Let hatred therefore depart from among you; let your quarrels end, let wars cease. Enter upon the road to the Holy Sepulchre; wrest that land from the wicked race, and subject it yourselves. That land which, as the Scripture says, 'floweth with milk and honey,' was given by God into the power of the children of Israel. Jerusalem is the centre of the earth."
When Pope Urban had thus spoken, all who were present cried out, "It is the will of God! It is the will of God!"
So began the epoch of the Crusades. There were many Crusades, at various periods, through two hundred years. Jerusalem was taken (1099), and lost again later (1187) -- and it was never regained by Christians till General Allenby captured it during the World War of 1914-18. Thus the Crusades failed in their main purpose, and their failure discredited the Church whose power they had at first so greatly increased.
Yet the Crusades had vast results. Through all these years, men of all classes -- kings, princes, barons, merchants, soldiers -- were travelling from Europe to the Holy Land, and there they came into close touch with the luxury and mystery of the East. They learnt much from the culture of the Saracens, and they brought back with them some of the luxuries of the East -- carpets, silks, spices, etc.
All this trade brought great wealth to the towns, especially to Venice and Genoa in Italy, and then to the Hanseatic (i.e. leagued) towns of Gemany.
Once again, during the Crusades, the East taught the West, as in the days of the ancient empires.