Books 13–16, some 2,970 verses long, form the fourth and largest of six units of four books each into which the Iliad naturally divides; such a unit would be suitable for oral performance on a single day as part of a six-day rendition of the whole (cf. Thornton, Supplication 46ff.). Like 5–8 and 9–12, books 13–15 open with a Greek success (from a weaker position each time), now led by the Aiantes and Idomeneus; but this is followed by losses even worse than those which closed 5–8 and 9–12. The ships are endangered, Protesilaos' is burned and, in a fourth recurrence of this same pattern of success and disaster, Patroklos, sent by Akhilleus to the rescue, is slain – all this in the single day that lasts from 11.1 to 18.239. Thus the Achaean defeat finally involves, in a most personal way, the hero who had done most to precipitate it. But this must not happen too fast: to delay it is a major function of book 13, anciently entitled ἡ ἐπὶ ναυσὶ μάχη, ‘the battle at the ships’.

By the neat device of having Zeus avert his gaze, the poet gives the panic-stricken Greeks ample scope for valour.