Scholars have long praised the overall topographic accuracy of Thucydides' account of the campaign at Pylos (iv 3–6, 8–23, 26–41); and among the numerous details mentioned, only two apparent inaccuracies have been identified, both involving measurements. One, an inaccurate estimate of the length of Sphakteria, has been previously explained as nothing more than a simple numeral corruption and is, in any case, irrelevant for understanding the military narrative. But the other, the underestimated width of the southern harbour entrance, remains a serious error which implies a fundamental misconception of relevant local geography and has made the account of Spartan strategy incomprehensible. Furthermore, its impact on the question of Thucydides' investigative methodology has been considerable, since most commentators, thinking the information reliably transmitted, have concluded that Thucydides never visited Pylos and somehow accepted misinformation on this crucial point. However, close study of the passage suggests that a textual corruption, not Thucydides, is responsible for the present inaccuracy.