in∙fi∙del "in-fə-del n: one who is not a Christian or who opposes Christianity.
The crusades of Medieval times were an attempt to take back what the Christians considered to be their holy land from the Muslims. The most important of these lands was Jerusalem. "Taking the Cross" meant for European noblemen to take arms for the Pope against the Infidel of Arabia, also known as the Saracen. To take the cross meant a complete pardon for past sins and favor gained in the eyes of the church. Although the crusades were for some a religious endeavor, for others it was a political move.
These crusades occurred between the years of 1096 and 1291. There were eight crusades in all. The first crusade was called for by Pope Urban II. Prior to the first crusade, the Byzantine Empire (Orthodox Christians) and their Islamic neighbors, the Saracens, had a relatively stable relationship with occasional small skirmishes. While the Saracens were in control of the holy city of Jerusalem, Christians were allowed to make pilgrimages there. However the coming of a new, more warlike and fearsome group of Muslims, the Seljuk Turks, took over control of Jerusalem and began to persecute the Christians there. These Turks invaded the Byzantine territory of the Anatolian peninsula and defeated the Byzantine army and killed their emperor at the Battle of Manzikirt in 1071. .
A new Emperor Alexius I seized control in 1081 and tried to rebuild the Byzantine Empire. Alexius I appealed for help from the West, namely the Pope Urban II. At this time the conquest of the Anatolian peninsula strained the political stability of the Muslim world. Recognizing this, Pope Urban II decided to not only answer Alexius I's appeal but to in fact, launch a much more ambitious plan than reclaiming the peninsula. He wanted to wrest back control of the city of Jerusalem from the Turks into Christian control. He also wanted to united the European monarchs under a papal banner.