Military history of the Crusader states
The Seljuk–Crusader War began when the First Crusade wrested territory from the Seljuk Turks during the Siege of Nicaea in 1097 and lasted until 1128 when Zengi became atabeg of Aleppo. At the latter date, the chief threat to the Crusaders from the east and north became the Zengids. The conflict was generally fought between European Crusaders and the Seljuk Turks and their vassals. The Muslim Syrian emirates occasionally allied themselves with the Christians against rival states.
Crosses in heraldry
Heraldry emerged in western Europe at the start of the 13th century out of earlier traditions.
The Christian cross was used as a field sign by the Christian troops during the Crusades. 
In 1188, Kings Henry II of England and Philip II of France agreed to launch the Third Crusade together, and that Henry would use a white cross and Philip a red cross. The red-on-white cross came to be used by the Knights Templar, and the white-on-red one by the Knights Hospitaller (also white-on-black); the Teutonic Order used a black-on white version. Early cross or spiral-like shield decorations, not necessarily with Christian symbolism, are already found on depictions of shields of the 11th century.