Patroclus dies for wearing Achilles' armor and going too far. When the Trojans reach the ships, the aged Nestor suggests that Patroclus ask Achilles for his armor, "in the hope that the Trojans, taking you for him, will withdraw from the fight." Patroclus makes the request, and the narrator comments that he "was going to ask for his own death, the baleful fate."
Achilles grants it, with one limit: after driving the Trojans from the ships, Patroclus must return, and he must not lead the attack all the way to Troy, "so that none of the gods who live forever, coming from Olympus, may intervene; for Apollo, who strikes from afar, loves them greatly." In prayer, Achilles asks Zeus to bring his friend back safe and sound, and Zeus grants only half: Patroclus will drive the war away from the ships, but will not return alive.
Patroclus puts out the fire on the ships, kills Sarpedon, son of Zeus, and pursues the Trojans to the wall. The poem says that he "committed a great madness" and that "the mind of Zeus is always stronger than that of men." Three times Apollo pushes him back from the wall and warns that fate does not want Troy to fall by his spear. Then the god himself strikes him from behind and disarms him, the Trojan Euphorbus wounds him, and Hector kills him. Dying, Patroclus says that Moira, Apollo, and Euphorbus killed him, and that Hector stripped him only in third place; he prophesies that Hector will soon die at the hands of Achilles.
The death of Patroclus has three causes that the poem does not separate: Zeus's plan, which had already been announced; Achilles' order, which sent him to fight in his armor; and Patroclus's own choice, which passes the limit. It is this death that brings Achilles back to war.