By 1094, Pope Urban II (1088-1099) received an appeal from Byzantine Emperor Alexius Comnenus for military assistance against the Turks in Anatolia. Urban had done much to restore Papal prestige after Gregory VII and the Investiture Controversy. While engaged in a papal tour of French dioceses, he stopped at Clermont on 27 November 1095, and Preached the First Crusade. The Muslim victories against the Byzantines and their constriction of pilgrimage to Jerusalem were said to be a disgrace to Christianity. Instead of pursuing strife among themselves, western nobles and knights should turn their efforts outward to the enemies of Christianity and the oppressors of the Holy Land. Thus, the Pope called for an armed pilgrimage, and those dying in the blessed campaigns of liberation would receive a heavenly reward.
Urban had been targeting mostly French nobles, and had wanted a well-disciplined body of knights under control of a Papal legate. Others were immediately attracted, mostly through itinerant preachers. Contrary to the Pope's wishes, the Peasants' Crusade began first, in the spring of 1096. It was lead by the most popular itinerant preacher, Peter the Hermit. Passing through France into Germany, its impoverished adherents survived by gifts and plunder. Met in Germany by more adherents and a few knights, it proceeded to plunder and destroy Jewish communities, in worms and Metz in particular. Upon reaching Hungary, the King Coloman would not tolerate their depredations, and routed a large segment of the force. When it arrived in tattered shape in Constantinople, the appalled Emperor ferried them across to Anatolia. The Turks soon annihilated them.
The knightly component of the Crusades was organized by the late summer of 1096. Henry IV of Germany and Philip I of France were excommunicated at the time, so the greatest kings of the West were not part of the Crusade. Urban appointed Adhemar, Bishop of Le Puy, as Papal legate and leader of the Crusader armies. The brothers of the kings of France and England--the 'second sons'--were prominent as Crusade leaders. These included Robert, duke of Normandy, and Hugh of Vermandois. The Flemmings and northwestern Franks were led by Baldwin of Flanders and his brother Godfrey of Bouillon, the Duke of Lower Lorraine. Raymond de St. Gilles led the southern French knights, while Bohemond, son of Robert Guiscard, gave up battling in Italy to join the Crusade.
They then left for Constantinople in several waves. Godfrey led his troops--as well as their bloated baggage train containing mendicants, pilgrims, merchants, and even prostitutes--along the Danube, through Hungary, into Bulgaria to Constantinople, barely avoiding serious entanglements with indigenous populations and warriors along the way. The Count of Toulouse fared much worse by taking a route through Italy, Venice, and along the Adriatic coast. On the way to Durazzo, the difficult terrain and war-like inhabitants caused his forces several losses as well as starvation. The Normans and northern French went through Italy, then crossed to Durazzo. When the whole host was arrived in Constantinople, Alexius did his best to get rid of them quickly. He quartered them outside of the city, supplying them with provisions and transportation to Asia Minor. He then told them to proceed along the southern coast of the peninsula, but they preferred to go right through its center. When they captured Nicaea in May 1097, the Emperor occupied it himself, claiming the surrounding areas for Byzantium.
At this point the Western army consisted, at the most, of 3,000 knights and 12,000 foot-soldiers. It split into two columns that were mostly autonomous. The northern force was under Robert of Normandy and Bohemond, while the southern group was commanded by Godfrey of Bouillon and Raymond of Toulouse. They soon learned why the Greeks had told them to avoid the interior--the Greek-Turkish combat, as well as Turcoman raiding, had denuded the countryside of provisions, and retreating Turks burned all else. Soon famine and drought was eating away that the armies. On July 1 at Dorylaeum in Western Anatolia, Turks and Crusaders met in battle. Bohemond's forces were initially bested by the light cavalry of the Turks. Much more agile than the knights and infantry, they were able to wear them down with arrow-fire for almost the entire day; by the afternoon, Turkish raiders were plundering Bohemond's base camp. Suddenly Godfrey's mounted knights appeared at the tops of the surrounding ridge, and the Turks were defeated by the two converging crusader columns. The victory at Dorylaeum cheered the crusaders and caused the Turks to avoid further contests at all costs, choosing instead to harass the columns as they moved east. When they reached Edessa in eastern Anatolia, Baldwin decided to break from the Crusade and establish his fief there. The rest of the host continued on to Antioch, where they settled down to a seven-month siege, and a mutual war of attrition with the Turks. Though the Christians defeated the two Seljuk releif armies, they were without siege engines or catapults, and were able to do little to undermine the city's defenses. Ultimately, though, Bohemond convinced one the of the Muslim tower guars to surrender it to him, and then proposed to his fellow knights that the first one to definitively establish a foothold in the city would have it as his own possession. Bohemond of course was the winner, and a few days after he assumed the title of prince, another Turkish relief force arrived under the amir Kitboga. The erstwhile besiegers were now under siege themselves. Under tremendous physical privation the crusaders barely survived, until the supposed discovery of a holy relic--the lance that had pierced the side of Christ during the Crucifixion--encouraged the Crusader host. On 28 June 1098, they burst out of the city and defeated the Turks.
Bohemond remained behind, and the crusaders continued the saga. They reached Jerusalem in June 1099. After a month-long siege they broke through, massacring the majority of the inhabitants--Muslim, Christian, and Jewish.