Greece was comprised of autonomous city-states (poleis), which included oligarchies as well as democracies. Despite the important political and social differences between city-states, these states shared a common language, worshipped the same gods, relied on the same Homeric epics as a guide to moral values, and shared cultural traditions at periodic panhellenic festivals. For these reasons, it is possible to speak of a common “Greek” set of cultural and religious values and norms. (1)
Although there are a handful of examples in our sources of treaties purporting to regulate the conduct of warfare, the Greek law of war was primarily an unwritten set of norms arising from Greek custom. There is one formal agreement from the classical period that addresses the conduct of war. In theory it applied to much of Greece but was largely ignored in practice. The Amphictyonic Council was an association including the majority of Greek city-states that was formed to protect and oversee the oracle and sanctuary at Delphi.
To say that the law of war was customary is not to imply that it occupied a lesser status in the eyes of the Greeks than written laws and treaties. Today customary international law, particularly in its traditional form that relies on states’ practice, is more controversial and contested than positive law in some quarters. The Greeks did not have this reaction to customary law. They used the same word?nomos?to refer to customs and written statutes.