On August 20, 1191, Crusader King Richard I the Lionheart killed approximately 3,000 Muslim prisoners from Acre at hill called Ayyadieh in full view of the Saladin's army. From the article:
"The Massacre of Ayyadieh occurred during the Third Crusade after the fall of Acre when Richard I of England had more than two thousand Muslim soldiers from the captured city killed in front of the Saracen armies of Saladin on August 20, 1191. Despite attacks by Muslim forces during the killings, the Christian Crusaders were able to retire in good order.
Massacre
After the fall of Acre, Richard I wanted to exchange a large number of Muslim prisoners from the city for the True Cross, 100,000 gold pieces and 1600 Christians held captive by Saladin.[1] A deal was struck and a deadline set for Saladin to fulfill his part of the deal.
Distrust between the two leaders developed and a breakdown of negotiations ensued, each side demanding that their opponent's hostages be released first. After the agreed time limit for the Saracens to handover the cross had expired, Richard, increasingly under the impression that Saladin was stalling, executed his hostages. On the 16th of August Richard ordered that all the prisoners from Acre should be taken to a small hill called Ayyadieh. There in full view of the Muslim army and Saladin's own field headquarters, around 3000 soldiers, men, women, and children from the city (according to Muslim sources) were put to the sword [2].
The massacre was controversial for contemporary Christian sources. The Itinerarium Peregrinorum estimated that 2700 Turkish hostages were killed but do not mention any non-combatants that were present [3]. Christian sources at the time take care to mention the strategic burden of the hostages as well as the transgressions of Saladin before the massacre was ordered. Baha ad-Din, a chronicler in Saladin's camp, indicates that even many of the crusaders disapproved of Richard's actions and cannot understand why Richard ordered the executions[4].
Parts of the Muslim Army became so enraged by the killings that they attempted to charge the Crusader lines but were repeatedly beaten back, allowing Richard I and his forces to retire in good order.
Aftermath
Any hope of regaining the True Cross disappeared after Ayyadieh; it was rumored that Saladin sent it to Damascus. By his orders the 2,300 Christian prisoners were executed in Damascus."