Thucydides is the author of one of the earliest and most influential works in the history of political thought. His subject was the conflict we now call the ‘Peloponnesian War’, the great war between Athens and Sparta and their respective allies, which lasted from 431 to 404 BC (with a break in the middle) and ended with the defeat of Athens and the dissolution of the Athenian empire. Thucydides saw this as a momentous and historic conflict, on an unprecedented scale, and he states his ambition of producing a full and objective account that will be ‘a possession for all time’. His book does indeed contain a very detailed record of the events of the war, which includes such famous set-pieces as Pericles’ Funeral Speech, the plague in Athens, the civil disorder in Corcyra, the debates on imperialism over Mytilene and Melos, and the disastrous failure of the Athenian expedition to Sicily. But through these narratives he also presents a sustained and sophisticated study of political power itself – its exercise and effects, its agents and victims, and the arguments through which it is justified and deployed.

This was a new kind of history – rationalistic in its purpose, self-conscious and explicit in its methodology – and Thucydides himself was very concerned to distinguish it from the work of his predecessors. But it would be anachronistic to classify his ‘history’ too narrowly. It was conceived in a fifth-century BC milieu of still emergent literary forms in drama, rhetoric, logic, physics and philosophy as well as in history (all these names of ‘subjects’ are derived from Greek words), and at a time when literacy was rare. Thucydides’ work draws on most of these other genres (as well as on the earlier model of Homer’s oral epic) and we do well to approach it free from the particular assumptions we bring to historical texts in our own culture.