The Crusaders made several key mistakes leading up to and during the Battle of Hattin, which contributed to their defeat. Here are the primary ones:

1. Breaking the Truce: One of the initial mistakes was the aggressive actions of Reynald of Châtillon, who repeatedly violated truces with the Muslims. His raids on Muslim caravans and an audacious plan to attack Mecca itself provoked Saladin and provided him with a casus belli, or just cause for war.

2.  Poor Strategic Decision: King Guy of Jerusalem, under pressure from the more militant factions within the Crusader states, decided to march his army to relieve the besieged city of Tiberias. This decision was made despite advice from more experienced military leaders like Raymond III of Tripoli, who suggested a more defensive strategy.
3.  Lack of Water and Supplies: The Crusader army faced a grueling march across arid terrain in the scorching heat of July without securing adequate water sources. Saladin’s forces strategically controlled the water sources, leaving the Crusaders parched and demoralized.
4.  Terrain Disadvantage: The Crusaders allowed themselves to be drawn into a battle on the Horns of Hattin, a location surrounded by rocky hills, which was unfavorable for their heavy cavalry and infantry formations. This terrain gave Saladin’s more mobile forces a distinct advantage.
5.  Failure to Protect the Rear: As the Crusader army marched, they failed to adequately protect their rear and flanks. This allowed Saladin’s forces to harass and weaken them continuously during their march, further sapping their strength before the main battle.
6.  Underestimating the Enemy: The Crusaders may have underestimated Saladin’s ability to unite various Muslim factions and his tactical prowess on the battlefield. Saladin’s strategy of continuous harassment, controlling water sources, and choosing the right terrain showcased his superior understanding of desert warfare.
7. Internal Divisions: The Crusader states were not a monolithic entity but a collection of principalities and territories with their own interests and rivalries. These internal divisions often led to conflicting strategies and priorities, weakening their collective military response.
8.  Over-reliance on Heavy Cavalry: While the heavily armored knights of the Crusader states were a formidable force, their effectiveness was reduced in the conditions of Hattin. The combination of heat, lack of water, and the terrain made it difficult for them to execute their traditional charge effectively.