The Iliad has twenty-four books, in verses of six feet called hexameters. The story covers only a few weeks of the tenth year of the Trojan War. The poem warns at the start that the war has already lasted a long time: in Book II, the omen of Aulis says that the Greeks would fight as many years as the birds devoured, "and in the tenth we will take the city."
The books group into blocks. Books I to IV bring Achilles' quarrel with Agamemnon, Zeus's promise, the catalogue of the armies, the duel of Paris and Menelaus, and the broken truce. Books V to VIII show Diomedes, the farewell of Hector and Andromache, the duel of Hector and Ajax, and Zeus's scale. In Books IX to XII are the embassy to Achilles, the Doloneia, and the assault on the wall.
Books XIII to XVII gather the battle by the ships, Zeus's deception by Hera, and the death of Patroclus. Books XVIII to XXII bring the shield of Achilles, the end of wrath, the battle of the gods, the river, and the death of Hector. The last two, XXIII and XXIV, are the funeral games for Patroclus and the ransom of Hector's body. At the end, Hector's body lies twelve days beside the ships before it is returned, as the god Hermes tells Priam.
This short time is a choice of frame. The poem does not tell the whole war: it begins with the wrath of Achilles and ends with the funeral of Hector, before the city falls. That is why it is common to read the poem as the account of a crisis, not of a campaign, in which each book advances the same conflict a little.