The present paper aims to assess the relevance of Thucydides’s study for international relations, viafocusing on his most eminent text, The Peloponnesian War. The analysis of its relevance will be donethrough a tripartite structure, in which the first two parts are symmetric. In a first part, the continuitiesbetween Thucydides’ historical account and the realist and neorealist theory of international relationswill be analysed. While in a second part, the continuities between Thucydides’ historical account andthe constructivist theory of international relations will be dealt with. Finally, in a third part a limit willbe raised, via the study of the prescriptive accuracy of The Peloponnesian War (on the grounds of newforms of violence).Key words: Peloponnesian war, realism, constructivism, International Relations, relevance, limit.