Proponents of just war theory claim that violent force should be used to protect innocent persons from attack. In contrast, pacifists maintain that war can never be just. Just war theory concerns the moral principles that indicate the justification and limitation of violent force. Drawing upon Roman ideas of just war, Ambrose and Augustine in the fourth and fifth centuries were the first Christian writers to develop a just war theory. A coherent theory based on cases that had been considered was first developed by Gratian in the twelfth century. This theory became the basis for international law. The criteria for going to war (jus ad bellum) include just cause, just authority, right intention, last resort, public declaration, probability of success, and proportionality. A favorable evaluation of proportionality means that the good to be achieved is greater than the evil to be suffered and inflicted. In addition, justice in the waging of war (jus in bello) has focused on two principles: proportionality in regard to the means of warfare rather than the ends; and discrimination or noncombatant immunity in regard to the damage to be caused by warfare. Contemporary Christian pacifism, including much pacifism in the Anglican Communion, comes not from absolute pacifism but from the judgment that modern warfare necessarily violates just war principles, particularly those of proportionality and noncombatant immunity.