The crusaders take Jerusalem

Jerusalem had passed from the Fatimids to Turkmen chiefs allied with the Seljuks in the 1070s; in 1098 the Fatimid vizier al-Afdal took it back from the Artuqid Ilghazi and installed Iftikhar al-Dawla as governor. The Fatimids, who saw the Seljuks as the common enemy, had sought an understanding with the crusaders, but these refused to stop short of Jerusalem. As they approached, Iftikhar al-Dawla expelled the city's Christians, poisoned the wells outside the walls and had the trees cut down. The crusaders — by Raymond of Aguilers's count about 1,200–1,300 knights and 12,000 foot soldiers — reached the city on 7 June 1099.

A first assault on 13 June failed for lack of siege engines. On 17 June Genoese and English ships at Jaffa brought timber and craftsmen, and in the heat of summer, short of water, the army built two siege towers. After a priest reported a vision, the crusaders fasted and on 8 July walked barefoot in procession round the walls to the Mount of Olives. The final assault began on 13–14 July; on 15 July the men of Godfrey of Bouillon broke through the northern wall, and the governor surrendered the Tower of David to Raymond of Toulouse in return for safe conduct to Ascalon.

The capture was followed by a massacre notorious even by the harsh standards of medieval warfare. Crusader eyewitnesses describe the Temple Mount running with blood; Fulcher of Chartres, who was not present, writes of 10,000 killed in the Temple area, and Ibn al-Athir, writing over a century later, gives 70,000, a figure considered a great exaggeration. The number of victims is a matter of debate: Conor Kostick considers 40,000 plausible, while other historians think the later sources exaggerated the scale. According to Ibn al-Qalanisi the Jews who took refuge in their synagogue were burned in it; a letter from the Cairo Geniza confirms that the synagogue was burned but not that anyone died inside, and other Geniza letters tell of Jewish captives ransomed by the community of Ascalon — some Jews and Muslims survived as fugitives or captives. The Dome of the Rock and the al-Aqsa Mosque became the Templum Domini and the Templum Salomonis. On 22 July Godfrey was chosen as ruler with the title of Advocate of the Holy Sepulchre, refusing to be called king, and on 12 August he defeated al-Afdal's relief army at Ascalon. Pope Urban II died on 29 July, before the news of the victory could reach him.