History of the Peloponnesian War, Volume II - Books 3–4

The Peloponnesian War was really three conflicts (431–421, 415–413, and 413–404 BC) that Thucydides was still unifying into one account when he died some time before 396 BC. Although unfinished and as a whole unrevised, in brilliance of description and depth of insight this history has no superior.