Thucydides’ account of ‘the war of the Peloponnesians and the Athenians, how they waged it against each other’ between 431 and 411 bc, has never been easy to read. At the end of the first century bc, in the earliest comments on the text that survive, Dionysius of Halicarnassus said that those who could master its Greek ‘are easily counted’. Lorenzo Valla, presenting his translation into Latin to the Pope in 1452, explained that the eight books into which it had come to be divided, ‘these eight towns, just so that you know this, my Imperator, for perhaps you know not what sort of towns you ordered me to take, are situated in the loftiest regions, in craggy mountains, and defy missiles, battering rams, ladders, trenches and the mines of sappers’. Thucydides knew, and made no apology. ‘The absence of the element of fable in my work may make it seem less easy on the ear, but it will have served its purpose well enough if it is judged useful by those who want to have a clear view of what happened in the past and what – the human condition being what it is – can be expected to happen again some time in the future in similar or much the same ways. It is composed to be a possession for all time and not just a performance-piece for the moment.’

Yet it stops suddenly, in mid-sentence, seven years before the war had ended (though there are insertions that Thucydides could only have made, if it was he who made them, when it had). And its style apart, the text is unusual. No one had written as he did, and no one was to do so in the same way again. It is more than a chronicle, recalls epic, has elements of tragedy and is intended to be of use; but Thucydides’ few conclusions do not convince and he does not say what its use might be. It falls across all our genres and is diminished when assigned to any.