" The founding of the military orders was the closing act of the drama begun by Constantine at the Milvian Bridge. Marching into Rome under the banner of the cross, he had taken a powerful and mysterious theology and bent it to his own purposes. It had promised unity; he needed unification. It had promised ultimate victory; he needed earthly victory at once. It had promised an identity that transcended nationality and language; he had needed to overcome nationalism. Most of all, he needed to convince his soldiers, the people of Rome, and the enemies who threatened him that he was driven by something higher and more noble than simple ambition. Probably he needed to convince himself as well.

Christianity gave Constantine freedom from guilt over his conquests at the same time that it lent him the zeal he needed to pursue them. Seven hundred years later, the military orders did exactly the same thing for the men who joined them and gave them a rule to spell out precisely what they would gain. That marriage of spiritual gain and political power would shape the next five centuries and the painful and protracted divorce between the two the centuries after that. "

― Susan Wise Bauer , The History of the Medieval World: From the Conversion of Constantine to the First Crusade