The first Athenian intervention in Sicily is one of the most opaque episodes in Thucydides. The historian for once dispenses with a full record and confines himself explicitly to the major events of the campaign. What then emerges is a disconnected narrative of geographically separate actions, most of them trivial. There is no attempt to give a synoptic picture or explain the problems of strategy, and the lack of coordination has (not surprisingly) impressed many critics. The episode is remarkable for another reason. For once we have that rarest of rare birds, an independent control source for Thucydides. Since 1930 there has been available a brief fragment of papyrus, usually ascribed to Philistus, which provides an extraordinarily detailed, if fragmentary, report of a portion of the campaign. The fragment has become a standard reference, and it is reported, not always accurately, in the more recent scholarship on the Peloponnesian War. But there has been little attempt to come to terms with the historiographical problem it poses. Not only does the fragment give a large amount of detail which has no counterpart in Thucydides, but its narrative, as it is usually interpreted, is formally inconsistent with Thucydides' chronology. The new fragment is most probably the work of a Sicilian historian, well acquainted with the events of 427/6, and it is – to put it mildly – disturbing to find a contradiction in what should have been an easily verifiable sequence of events.