The Crusades Explained: Causes, Campaigns and Consequences

The Crusades, in Wikipedia's definition, were a series of military campaigns launched by the papacy between 1095 and 1291 against Muslim rulers "for the recovery and defence of the Holy Land", as part of a wider crusading movement that later turned against pagans, Christian dissidents and the papacy's other enemies. That 196-year core runs from a pope's sermon in central France to the fall of the last crusader strongholds on the Levantine coast.

The world Urban II spoke into

Wikipedia's background section explains why the call landed when it did. Jerusalem had been under Muslim rule since Caliph Umar took it in 638, and by the mid-tenth century three rival caliphates had emerged — Umayyad, Fatimid and Abbasid, compared in the early caliphates. In 1071 the Seljuk leader Alp Arslan crushed the Byzantines at Manzikert, opening Anatolia to Turkoman migration.

In the Latin West, church reformers had strengthened the papacy, the 1054 mutual excommunications had divided Catholic West and Orthodox East, and theologians working under Gregory VII had concluded that dying in a just war equated to martyrdom. Penitential pilgrimage to Jerusalem was popular, and attacks on pilgrims were increasingly frequent. In March 1095 envoys from the Byzantine emperor Alexios I asked Urban II for military aid at Piacenza.

Clermont, 27 November 1095: one speech, several versions

At the Council of Clermont on 27 November, Urban announced a campaign against the Turkomans. Wikipedia notes accounts differ on whether he promised reduced penance or full remission of sin, and that the crowd "reportedly" cried Deus vult — "God wills it!"

Fordham University's Internet Medieval Sourcebook shows why everything is hedged. "The acts of the council have not been preserved," it notes; what survives are accounts by chroniclers — Fulcher of Chartres, Robert the Monk, the anonymous Gesta Francorum, Balderic of Dol and Guibert of Nogent. The versions differ. Fulcher's has Urban promise that those who die fighting "shall have immediate remission of sins". Robert's, written "perhaps 25 years after the speech", is the one with the crowd crying "It is the will of God!" — and the Sourcebook notes Robert used the Gesta as a source, as did Balderic. So agreement between some versions is partly copying. That is the problem set out in primary and secondary sources and in spotting bias in history writing.

The First Crusade and the Crusader states

Popular enthusiasm outran Urban's plan. Wikipedia describes Peter the Hermit's followers setting out from March 1096 and the anti-Jewish Rhineland massacres led by Count Emicho, beginning at Speyer on 3 May 1096. Kilij Arslan destroyed the People's Crusade at Civetot on 21 October.

The princes' armies followed. Antioch fell after a long siege in June 1098, and Jerusalem was taken on 15 July 1099; over the next two days, Wikipedia says, the crusaders "slaughtered the population and looted the city". Four Crusader states resulted: Edessa, Antioch, Tripoli and the Kingdom of Jerusalem.

Worked example. Wikipedia's figures show how much of the army was left by the end. At Constantinople the host numbered 60,000–100,000, including 30,000 non-combatants. About 40,000 reached Antioch. At Ascalon on 12 August 1099 roughly 9,000 infantry and 1,200 knights fought — 10,200 in total, about 25.5 per cent of those at Antioch and between 10 and 17 per cent of the range counted at Constantinople. After most went home, Godfrey of Bouillon was left with 300 knights and 2,000 foot soldiers. All of these figures are estimates; the percentages are only as good as the counts behind them.