While the Achaian and Trojan armies group for battle, Zeus calls for an assembly of all the gods. When they have gathered, he gives them permission to openly assist either of the factions, for Achilles must be prevented from overstepping the bounds that fate has set on his achievements. At once, Hera, Athena, Poseidon, Hermes, and Hephaistos leave to join the Achaians, while Ares, Apollo, Artemis, and Aphrodite fly to the side of the Trojans.
The battle opens with great fury. Achilles is about to kill Aeneas when Poseidon rescues the Trojan prince. Poseidon does so because Aeneas has been fated to be the sole survivor of the house of Priam. But, undaunted by divine interference of Poseidon, Achilles continues fighting, slaughtering many of the Trojans and sweeping through the field unchecked. Many Trojans die at his hands.
Book XX serves as an interlude before the aristeia of Achilles in Books XXI and XXII, which culminates in the death of Hektor. The council of the gods at the start of Book XX sets up the fighting (theomachy) between the pro-Greek and pro-Trojan deities that continue into Book XXI.
A much commented-on section of Book XX deals with Aeneas. Aeneas' fame today, of course, comes from Virgil's great epic, The Aeneid, which was modeled on Homer's works. Aeneas is introduced early on in the Iliad, but up until Book XX he plays only a minor role. In this book, his prominence serves only as a dramatic diversion whereby Homer delays the fight between Hector and Achilles.
At line 345, Poseidon prophesies that Aeneas will survive the battle. Ironically, because of Virgil, Poseidon's prophecy is true in a much greater way than Homer could possibly have intended: The Trojan survivor becomes one of the great epic heroes of world literature. One theory exists that the section on Aeneas was added to the Iliad to honor a Greek family that claimed descent from Aeneas. Whatever the validity of that idea, the Roman Empire eventually claimed Aeneas as its founder, through the Julian line. From that tradition, Virgil chose to create his epic character.
The aristeia of Achilles begins in the last part of Book XX and continues in the next two books.
theomachy a battle of the gods, frequently used in mythological traditions.
threshing floor floor or platform where seed was separated from a plant by striking the plant against the hard surface.