The aristeia of a warrior is defined simply as that warrior's greatest battle, the battle in which he reaches his peak as a fighter and hero. Throughout the Iliad, many of the characters have aristeias; Book V is the aristeia of Diomedes.
Book V, sometimes referred to as the Diomedia, has its own internal unity and may once have constituted an independent poem, or bardic lay, about the exploits of the Achaian hero Diomedes, which was adapted by Homer and included in the Iliad. The long account of the deeds of Diomedes has little to do with the main plot of the Iliad in any direct sense and could easily have been omitted or given in less detail, but it has several important artistic functions. Diomedes is a heroic Achaian figure, comparable to Achilles in prowess, gallantry, courage, and divine favor, but with the significant difference that he is always courteous, self-controlled, and respectful, even when in dispute with his king, Agamemnon. The tale of Diomedes presents an alternative model of a hero with whom to compare Achilles and by which to judge Achilles' defection from the army during the heat of battle. Diomedes has no more reason to fight for Menelaos than Achilles has. Diomedes has not received war prizes that equal those of Agamemnon or Achilles. Yet when battle arises and he is called upon to do his duty, Diomedes fights with unmatched intensity. Achilles sits in his tent. Additionally, the Diomedia is the first and most impressive of the long series of battle scenes and scenes of personal combat that now follow in the absence of Achilles.
