The Siege of Jerusalem took place from September 20th to October 2nd 1187, when Balian of Ibelin surrendered the city, resulting the absolute conquer of the Kingdom of Jerusalem by Saladin. This conquer was the excuse to launch the Third Crusade in 1189.
After days of Muslim attacks with hundreds of casualties, Saladin decided to move his camp towards the Mount of Olives, where Jerusalem´s wall was lighter. The walls were constantly pounded by the siege engines, catapults, mangonels, petraries, Greek fire, crossbows, and arrows. Finally, the wall was mined and the crusaders were incapable of pushing Saladin´s troops back from the breach, although the Muslims couldn´t either gain entrance to the city.
The civilians were in great despair, and finally Balian had to surrender the city unconditionally.