While Jerusalem had been under Muslim rule for hundreds of years, by the 11th century the Seljuk takeover of the region threatened local Christian populations, pilgrimages from the West, and the Byzantine Empire itself. The earliest initiative for the First Crusade began in 1095 when Byzantine emperor Alexios I Komnenos requested military support from the Council of Piacenza in the empire's conflict with the Seljuk-led Turks. This was followed later in the year by the Council of Clermont, during which Pope Urban II supported the Byzantine request for military assistance and also urged faithful Christians to undertake an armed pilgrimage to Jerusalem.

Jerusalem was reached in June 1099 and the Siege of Jerusalem resulted in the city being taken by assault from 7 June to 15 July 1099, during which its defenders were ruthlessly massacred. The Kingdom of Jerusalem was established as a secular state under the rule of Godfrey of Bouillon, who shunned the title of 'king'. A Fatimid counterattack was repulsed later that year at the Battle of Ascalon, ending the First Crusade. Afterwards the majority of the crusaders returned home.