Thucydides is a foundational author in the history of political thought. He stands at the very start of reflective thinking about politics in the western tradition and that in itself gives his voice a great freshness, force and originality. But it also presents us with some immediate problems of understanding, since the sort of distinctions we now make between political science, political theory, political history and the study of international relations did not exist in his day, though he has on occasion been claimed as the originator of each of these modern ‘subjects’.

One key aim of this series is to present each author and text in their proper cultural and historical context and to avoid importing into our understanding of them anachronistic concepts derived from later developments and theories. I have tried to take this objective seriously in various ways. First, and perhaps controversially, I have not called the text by its traditional title, ‘The Peloponnesian War’, which is not a title we have any evidence Thucydides himself used and which was seen to be one-sided even in his own time. Secondly, in structuring the work I have given precedence to the internal divisions by years and campaigning seasons that Thucydides chose to employ rather than the conventional division into ‘books’, which was again a later addition (though I have retained the latter as background headings for ease of cross-reference within the text and to the secondary literature). These two tactics are intended to help prevent us projecting false assumptions on to the work even before we start reading it.