The capture of Jerusalem by the Khwarezmians in August had caused great alarm among both the Christian and the Muslim states. Al-Mansur, the Emir of Homs and an-Nasir Dawud, ruling Kerak, joined the Templars, the Hospitallers, the Teutonic Knights, the Order of Saint Lazarus and the remaining forces of the Kingdom of Jerusalem to take the field against the Egyptian Sultanate.
The two armies met near La Forbie, a small village northeast of Gaza. On the allied side, Al-Mansur was present in person, commanding about 2,000 cavalry and a detachment of troops from Damascus. The overall Christian command was given to Walter IV of Brienne, Count of Jaffa and Ascalon, although Robert of Nantes, Patriarch of Jerusalem, and Philip of Montfort, Constable of Jerusalem, were also present. The Christian army consisted of about 1,000 cavalry and 6,000 foot soldiers. The Transjordanian forces were under the command of Sunqur al-Zahiri and al-Waziri, and consisted of about 2,000 mounted Bedouin. The Egyptian army was commanded by a Mamluk officer named Baibars which was slightly inferior in strength to its opponents.
Al-Mansur advised the allies to fortify their camp and take the defensive, waiting for the undisciplined Khwarezmians to disperse and leave the Egyptians at a considerable disadvantage. However, Walter, to whom the overall command had been given, was unwilling to refuse battle when he had the advantage of numbers, a rarity for the Christians of Outremer. The allied dispositions were as follows: Christians on the right wing, near the coast, the Emir of Homs and the Damascenes in the center, the Bedouin on the left.