Contradictory views merit examination of the cooperation between the Templar and Hospitaller military orders buring the Crusades. The rules laid down by the Orders contain much information on their mode of coexistence in the East.
Half a dozen of articles of the Rule of the Temple deals with the behavior to be adopted in the presence of Hospitallers, devoting quite some to battles. During battle a wounded Templar could join the first Christian banner available, preferentially choosing that of the Hospital. (...)
The military orders soon became accustomed to collaborating on the battle fields of Palestine, whether in Hārim (1164), Montgisard (1177), Margelion (1179), La Fontaine du Cresson, and finally Hattīn (1187). Their first combined operation dates back to the siege of Damascus, led by the armies of the second crusade in 1148. (...) The same determination allowed in 1163 a contingent of Crusaders to unblock, with the support of Templars, the Hospitaller castle of Crack des Chevalliers, that was besieged by the Atabeg of Damascus, Nūr ad-Dīn. (...)
The fraternity of arms reigning between the Knights Templar and the Hospitallers also appears from the Battle of La Fontaine du Cresson on May 1, 1187, where the Grand Masters Gerard de Ridefort and Roger des Moulins fought side by side. Templar Grand Master Gérard de Ridefort did not listen to the precautionary advice of the Hospital master when deciding to engage in an unequal fight against a column of 7,000 Muslims on the verge of to regain its bases. Hospitaller Grand Master Roger des Moulins was killed along with sixty Templars. (...) Gerard de Ridefort escaped the Ayyubid swords in pitifully fleeing, as his subordinate had prophesied at the start of the fight. This same great master caused the fall of the Frankish Holy Land, a few weeks later, prompting Guy de Lusignan to reluctantly help the city of Tiberias, besieged by Muslims. The battle of Hattīn (4 July, 1187) was fatal to the Latins who lost 230 Templars, beheaded by order of Saladin, and 120 Knights of the Hospital.
This blog is based on the paper (in French) on "Combined operations of the military orders in the Medieval Levant (12th-13th centuries)" by Pierre-Vincent Claverie; illustration source