Birth of the Crusades: the Council of Clermont, 1095
The Seljuk Turks and the Threat to Byzantium
The catalyst for the First Crusade came from the east, where a new and powerful force had transformed the political map of the Middle East. The Seljuk Turks had swept out of Central Asia in the early eleventh century, converting to Sunni Islam and rapidly building an empire that stretched from Persia to Syria. In 1055 they entered Baghdad, making themselves protectors of the Abbasid caliph.
The decisive moment for the Byzantine Empire came at the Battle of Manzikert in 1071. A Byzantine army under Emperor Romanos IV Diogenes met the Seljuk forces of Sultan Alp Arslan in eastern Anatolia. The Byzantines suffered a catastrophic defeat: Romanos was captured, the Byzantine army was routed, and much of Anatolia — the heartland of Byzantine military manpower — fell under Seljuk control. By the 1090s the Seljuks were camped at Nicaea, barely 100 kilometres from Constantinople itself.
The Battle of Manzikert (1071) was a turning point in the origins of the Crusades. The Byzantine defeat opened Anatolia to Seljuk settlement, cutting off Byzantine military recruitment and threatening Constantinople. It created the crisis that prompted Emperor Alexios Komnenos to appeal to the West for help.
The Appeal of Alexios Komnenos
Alexios Komnenos became emperor in 1081 and proved a capable ruler, stabilising Byzantine finances and military power. But the Seljuk threat remained serious. In 1095, Alexios sent envoys to the Council of Piacenza, asking Pope Urban II for military mercenaries to help him recover Anatolia. Alexios wanted trained professional soldiers — knights who would fight under his command, recover land, and return home. What he got was something far bigger and far harder to control.
Why did Urban II respond so dramatically? The pope saw an opportunity to extend papal authority eastward, perhaps even to reunite the Eastern and Western Churches (which had formally split in 1054 in the Great Schism). A successful expedition would burnish papal prestige, redirect the violence of European knights from tearing apart Christian society, and fulfil the duty of protecting pilgrims to Jerusalem. Urban was thinking not just as a defender of Byzantium but as the leader of all Christendom.
The Council of Clermont, November 1095
In November 1095, Pope Urban II held a church council at Clermont in central France. On 27 November, at the end of the council, Urban addressed a large crowd gathered outside the city. His speech was a defining moment in medieval history. No verbatim record survives — accounts were written down years later by different chroniclers — but the sources agree on its key elements.
Urban described the sufferings of Eastern Christians under the Seljuks. He called on the knights of the West to stop fighting each other and turn their military skills toward a holy purpose. He urged them to march to Jerusalem and liberate the Holy Sepulchre, the site of Christ’s tomb, from Muslim rule. He promised that those who died on the journey would receive a plenary indulgence — full remission of all sins. According to chroniclers, the crowd responded with the cry Deus vult — “God wills it”.
Urban II’s offer of a plenary indulgence at Clermont was revolutionary. Medieval Christians believed that sins had to be expiated through penance in this life or suffering in purgatory after death. Full remission of all sins was an extraordinarily compelling promise, removing the greatest spiritual fear of a medieval person.
Historians debate whether religious devotion or material self-interest drove crusaders. Recent scholarship has emphasised genuine religious motivation: crusading was extremely expensive and dangerous, and most crusaders made a financial loss. However, individual motives were clearly mixed.
Religious motives included the desire for spiritual reward through the indulgence, a genuine devotion to the Holy Sepulchre, and the concept of pilgrimage-combined-with-warfare (the crusade was, legally and spiritually, a form of armed pilgrimage). Social and secular motives included the prospect of land and wealth in the East for younger sons who could not inherit at home, the desire for adventure and glory, and loyalty to lords who had taken the cross. For many, religion and self-interest were genuinely inseparable.
The Rise of Militant Christianity
The idea of a holy war did not emerge fully-formed at Clermont. It had roots in earlier papal campaigns. In the 1060s and 1070s, popes had granted spiritual rewards to knights fighting Muslim rulers in Spain and Sicily. The Cluniac reform movement had gradually created a Christian culture in which the concept of a “soldier of Christ” was not just metaphorical but potentially literal.
Urban II synthesised these ideas at Clermont. By framing the expedition as a holy pilgrimage — not merely a war — he gave crusaders both spiritual reward and a sense of moral legitimacy. Knights who worried that killing was sinful could now believe their swords served God. The response across France, Flanders, Lorraine, southern Italy and England was enormous: nobles, knights and even poor pilgrims began to take the cross.
Urban II intended his call to be directed at trained knights. But the response went far beyond the noble class. In spring 1096, a charismatic preacher named Peter the Hermit gathered a large following of poor pilgrims, minor knights and common people. This “People’s Crusade” set off months ahead of the official crusade army. Lacking supplies, discipline and military experience, Peter’s followers swept through Germany, massacring Jewish communities along the Rhine (the Rhineland Massacres of 1096) before crossing into Byzantine territory. The People’s Crusade was destroyed by the Seljuks in Anatolia in October 1096 before the main army had even left Europe.
The Rhineland Massacres — in which Jewish communities at Worms, Mainz and Cologne were attacked — revealed a dark consequence of the crusading ideology. The same militant Christianity that could be directed against Muslims in the East could also be turned violently against religious minorities at home. This connection between crusading and religious intolerance would recur throughout the era.