This study has explored the assertion that an ancient law of nations had the traits of a primitive legal system. After considering the sources of international legal obligation in antiquity, I have reviewed the three essential areas in which law influenced ancient State relations: (1) the reception of envoys and the protection of aliens living in ancient States; (2) the making and enforcement of treaties; and (3) the rules governing the declaration of war and the actual conduct of hostilities. I have not merely sought to catalogue instances where ancient States apparently recognized these doctrinal features of a law of nations. Instead, the object has been to establish recurrent patterns of thinking and practice concerning these doctrines.

This study has thus scrupulously avoided the conclusion that there was a single, cohesive body of rules for a law of nations, recognized by all States in antiquity or that such rules were proximate to those that we regard today as being part of “modern” international law. Instead, I conclude that there was a common idea held in antiquity that international relations were to be based on the rule of law. The embrace of that idea, and not any particular structure of process or doctrine, is what qualifies ancient international law as something more than “primitive.”

It remains to elaborate these points by responding to the two most prevalent critiques of the idea that ancient international relations were based on a rule of law.