Greek customary law of war drew a clear distinction between intra-Greek wars, i.e. the armed conflict between adversaries which shared cultural and religious ties, and wars with opponents who were not part of the Ancient Greek world. The rules of warfare pertaining to conflict between Greek city-states contained rules for male soldiers, which included rules on sparing the lives of other Greeks, but also, those pertaining to women. This paper explores the participation of women in warfare, as well as the customary rules concerning rape, which can be deemed to have the force of law in armed conflict. In conclusion, a humanization of warfare may be recognized, albeit bearing in mind the concept of international relations and factors that affected the ancient customary rules of warfare.