Thomas Arnold (1795-1842) first published Volume 3 of his edition of Thucydides' History of the Peloponnesian War in 1835. It contains Books 6-8 of the History, covering events from the Athenian Sicilian expedition, which began in 415 B.C.E., to the battle of Cynossema in 411 B.C.E. The text and apparatus is based on the third edition of Bekker (1832). However, Arnold freshly collated a number of Greek manuscripts, including the important tenth-century Laurentian manuscript, which led to some revision of Bekker's text. Arnold's major contribution to Thucydidean scholarship lies in the detailed topographical and historical notes accompanying the text, which explain the geographical and political background to the History. For many generations Arnold's work has provided an indispensable guide through the complex geo-political context of the History, enabling students to appreciate its narrative, language and place in historiography.