For centuries, religion has been a fundamental concept that has had the power to unite many individuals and give them a sense of belonging. For thousands of years, polytheism was a very popular religious affiliation until the transition to monotheism. Belief in one god represented an important change in history, especially when considering Christianity. The unity of faith for Christians has been an ideal from the beginning. On the other hand, Islam and its followers, the Muslims, are united in faith and practice because of Allah, or God. Since the dawn of Christianity, the main pilgrimage destination has been the Holy Land and one of the places more sacred. it is Jerusalem: it is said that Jesus was crucified and buried here. After the Arabs conquered Jerusalem from the Byzantines in 638, Christians were still allowed to travel to the country as the Muslims were quite tolerant of their visitors. However, in the 11th century, things got worse and the Christians decided to reconquer their Holy Land. In turn, the First Crusade sought to take back what was theirs. In 1095, Pope Urban II received a letter from the Byzantine emperor Alexios I Komnenos, requesting assistance against the Seljuk Turks who had conquered lands in Asia Minor, Syria, and Palestine. Even before Urban received the call for help, he had learned that the Church of the Holy Sepulcher had been destroyed by a Muslim leader in Jerusalem. The church was later rebuilt around 1040. False stories of mistreatment of Christians quickly spread throughout the West. But the Muslims actually took advantage of the Christians who came to pray in the Holy Land and were forced to leave them alone. Nonetheless, the Pope believed that...... middle of paper......witnesses and participants. Princeton, 1921. “Crusader Letters Written from the Holy Land.” In translations and reprints from the original sources of European history. Dana Carlton Munro, tr. ed ed., vol. 1, no. 4. Philadelphia: University of Pennsylvania Department of History, 1900.Marcus, Jacob. The Jew in the Medieval World: A Sourcebook, 315-1791. New York: JPS, 1938. Munro, Dana C. “Urban and the Crusaders.” Translations and reprints from the original sources of European history. Vol 1:2. Philadelphia: University of Pennsylvania, 1895.Phillips, Jonathan. Holy Warriors: A Modern History of the Crusades. New York: Random House, 2009.Riley-Smith, Jonathan. "The Mood of the Crusaders in the East, 1095-1300." In The Oxford Illustrated History of the Crusades, edited by Jonathan Riley-Smith. Oxford: Oxford University Press, 2001.