The Byzantine Emperor Alexius I asked for help to defeat the Seljuk Turks, who were Muslims.
Seeing a great opportunity to provide papal leadership, Pope Urban II responded to the request by rallying warriors of Europe to liberate Jerusalem and the Holy Land (Palestine) from the infidel (nonbelievers) Muslims.
These series of Expeditions are known as the Crusades .
The word crusade, which is derived from the Latin crux ("cross"), is a reference to the biblical injunction that Christians carry their cross.
Crusaders wore a red cloth cross sewn on their tunics to indicate that they had assumed the cross and were soldiers of Christ. It made all crusaders, irrespective of rank or background, appear to be a unified army. It reminded the crusaders that they were fighting a holy cause. The red cross was added to flags and banners.
Nobles hoped to add to their personal fortunes and strengthen the power of monarchs.
For knights, this was a chance to use their fighting skills, something they enjoyed and did well. They were delighted to have such a worthy battle to fight. They also wanted to defend Jerusalem, the “fief of God”.
For peasants, this was a chance to escape from their dreary life in the feudal system. The pope promised that if they died while fighting a holy crusade, they would automatically be welcomed into heaven.
For others, it was a chance to have an adventure, and perhaps even to get rich.
Robin of Loxley (Robin Hood) returns from fighting the 3 rd Crusade. While King Richard is also away, his brother John, is a corrupt leader. Robin defies John and becomes an outlaw until King Richard returns.