The 11th century saw an increased zeal for pilgrimages, and from this time travelers to the Holy Land were very numerous. For greater security they often joined themselves in companies and marched under arms. It needed little to transform such pilgrims into crusaders.
Holy Land Pilgrimage - Abuse of the pilgrims by the Turks
The Arab conquest of the Holy Land had not interrupted the stream of pilgrims, for the early caliphs were more tolerant of unbelievers than Christian emperors of heretics. But after the coming of the Seljuk Turks into the East, pilgrimages became more difficult and dangerous. The Turks were a ruder people than the Arabs whom they displaced, and in their fanatic zeal for Islam were not inclined to treat the Christians with consideration. Many tales floated back to Europe of the outrages committed on the pilgrims and on the sacred shrines venerated by all Christendom. Such stories, which lost nothing in the telling, aroused a storm of indignation throughout Europe and awakened the desire to rescue the Holy Land from the grasp of the "infidel."
Holy Land Pilgrimage - The Christian and Infidel in the Holy Land
The ranks of the crusaders were constantly filled by fresh bands of pilgrim knights who visited Palestine to pray at the Holy Sepulcher and cross swords with the infidel. In spite of constant border warfare much trade and friendly intercourse prevailed between Christians and Moslems. They learned to respect one another both as foes and neighbors. The crusaders' states in Syria became a meeting-place of East and West.