In 1244, the Ayubid Sultan granted the Khwarazmiyya the permission to attack Jerusalem. The Khwarazmiyya forces began their siege of Jerusalem from 11 July 1244. The city’s defenses fell rapidly. On 15 July 1244, the Khwarazmiyya entered the city. There was extensive looting and killing and by the time the Khwarazmiyya left, the city was in such bad shape, with the streets choked with rotting corpses, that the place seemed unfit for human habitation. When the news of the pillaging and massacre at Jerusalem reached Western Europe, King Louis IX tried to organize a Seventh Crusade to the Levant. But the crusaders would never be able to retake Jerusalem.
The remaining forces of Jerusalem rallied around the Crusading orders and they clashed with the army of the Ayubid Sultan in the Battle of La Forbie (also known as the Battle of Hiribya), which began on October 17, 1244. After the experience of Khwarazmiyya’s sack ofJerusalem, the crusaders realized that no mercy would be shown to them if they lost. They fought bravely, since they knew that defeat meant death or enslavement, but the Sultan’s forces had overwhelming numerical superiority, and the crusader resistance collapsed on October 18. Over 5,000 crusaders had died, 800 prisoners were taken, including Walter of Brienne, William of Chastelneuf, Master of the Hospital, and the Constable of Tripoli.
After the fall of Jerusalem and the decisive defeat in the Battle of La Forbie, the remaining Crusader states in the Levant were in a bad shape. But instead of becoming united to face the external enemy, in Acre, they became embroiled in an internal war. This was the War of Saint Sabas, which pitted the shipping interests of Venice against the shipping interests of Genoa. The Venetians and the Genoese quarters in Acre were separated by a neutral stretch of land belonging to the monastery of Saint Sabas. For several years, the Venetians and the Genoese had been petitioning the Papacy in Rome to be granted possession of the monastery and its territory.
It is not clear to which party the Papacy had granted the monastery’s territory, since the Papal records of this momentous decision are missing. But both Venetians and the Genoese were able to flourish in Acre the papers which showed that they had the exclusive papal grant to the territory of Saint Sabas. Each side accused the other side of foul play and a war broke out. By 1256, the people in the Kingdom of Acre had forgotten that they faced the threat from the Islamic forces—they were too busy choosing sides in the battle between the Venetians and the Genoese. The Teutonic Knights sided with the Venetians while the Hospitallers sided with the Genoese. Between 1256 and 1260 most intense fighting took place. Many sections of Acre were ruined. Most of its defensive towers were destroyed.
The final fall of Acre came in 1291. The Mamluks besieged Acre in April 1291, and by May 18 they had breached its defenses. The crusaders, their families, and the local residents made a mad dash for the harbor to escape the invading army, but most were killed or enslaved. Many of those who made it into the boats drowned when the boats capsized due to overcrowding. A Templar stronghold was the last to fall. It held out till May 18, when the Templars surrendered after accepting a truce offer. But they were promptly executed.