proper declaration of war, performed by the fetiales priests (see also VII.3), was essential for Rome. Without a reasonable justification, going, morally wrong and liable to be punished by the gods. The list of allowed reasons for going to war was well-defined and fairly limited. Rome was allowed to seek redress if it had been done an injury, e.g. Roman territory or citizens had been robbed or plundered (clearly a law going back to a very early stage in Roman history). This was also valid for Roman allies - if one of them had been treated similarly, Rome was justly allowed to go to war, come to the defence of its ally, and settle the affair. Rome might even take away the ability to fight from “the wicked” and thus protect the rest of the world and spread civilization. It is easy to see how such reasoning might be abused, something that the Romans themselves remarked upon as well. In a speech that is likely fictitious and put into the mouth of a possibly equally fictitious character, Tacitus famously has the Celtic chieftain Calgacus say before the battle of Mons Graupius that “They [the Romans] make a desert and call it peace”.
