Christian military orders appeared following the First Crusade. The foundation of the Templars in 1120 provided the first in a series of tightly organised military forces which protected the Christian colonies in the Middle East, as well as fighting non-Christians in Spain and Eastern Europe.
The principle feature of the military order is the combination of military and religious ways of life. Some of them like the Knights of St John and the Knights of St Thomas also cared for the sick and poor. However they were not purely male institutions as nuns could attach themselves to a convent of the orders. One significant feature of the military orders is that clerical brothers could be, and indeed often were, subordinate to non-ordained brethren.
The role and function of the military orders has sometimes been obscured by the concentration on their military exploits in Syria, Palestine, Prussia, and Livonia. In fact they had extensive holdings and staff throughout Western Europe. The majority were laymen. They provided a conduit for cultural and technical innovation, for example the introduction of fulling into England by the Knights of St John, or the banking facilities of the Templars.
Joseph von Hammer in 1818 compared the Christian military orders, in particular the Templars, with certain Islamic models such as the shiite sect of Assassins. In 1820 Jose Antonio Conde has suggested they were modelled on the ribat, a fortified religious institution which brought together a religious way of life with fighting the enemies of Islam. However popular such views may have become, others have criticised this view suggesting there were no such ribats around Palestine until after the military orders had been founded. Yet the innovation of fighting monks was something new to Christianity.
(The date given is that for militarisation)