“There were no more than 12,000 crusaders that, in July 1099 after a three year campaign, got to camp under the walls of Jerusalem. Their emotion in sighting the sacred city changed into surprise when the presiding Muslim garrison declared to be ready fot an armistice. That garrison wasn’t Turkish but Arab, because the previous year Jerusalem had been retaken from the Selgiuchi by the Fatimidi, who had never confronted the Franchi. But they didn’t accept the offer perhaps because they thought a non-violent negotiation would have ruined their triumph. Therefore they demanded unconditional surrender.

The defenders, about 1000 men, resisted for 40 days. Then they surrendered. A witness present, Raimondo de Agiles, famous for his zeal described the scene as they were beheaded, killed by harrow or thrown from the towers. Others were tortured for days and days and then torched. The streets were strewn with heads, chopped hands and feet.”

"Those marvelous things lasted until the total consummation of the 70 000 citizens of Jerusalem, including the Jews, who were crowded and burned inside the synagogues.
Then the crusaders gathered in the grotto of the Santa Sepolcro that had hosted the remains of Christ, who had come into the world to preach “misericordia”, there they cried joyfully feeling worthy of him.”

--From vol. 7, pg. 112 of Storia D’Italia by MontanelliOn the first crusade year 1099