The armies of Baudouin III, King of Jerusalem besieged the city for four months. On August 13th, the crusaders managed to destroy a part of the city walls.
Bernard de Tremelay, Master of the Temple, rushed into this breach and prevented other Franks from entering the city. (After the seize of Gaza, in 1149, it seemed that the Templars wanted to keep Ascalon for themselves, or, at least, the profits and looting.)
The greed of Bernard de Tremelay was his downfall. He was killed in an ambush set by Turks in the city. His body, and those of his forty knights, were hung from the city walls.
The city finally fell on August 19th 1153.
Another narrative about this episode mentions that Bernard de Tremelay and his knights rushed the breach to stop the Frankish army being decimated by the ambush planned by the Turkish inhabitants. In this version of history the Templars sacrificed themselves to prevent a disaster.