The theme of man's mortality is introduced immediately into the poem in its opening lines:
Rage--Goddess, sing the rage of Peleus son Achilles,
murderous, doomed, that cost the Achaceans' countless losses,
hurling down to the House of Death so many sturdy souls,
great fighters' souls, but made their bodies carrion,
feasts for the dogs and birds,
and the will of Zeus was moving toward its end.
This will be a tale of death, with mortal bodies destroyed and souls released to make their spiritual journeys. Thus man lives in a mortal state, his fate determined by "the will of Zeus." Death will not be glorified here; broken bodies left on the field of battle will become "feasts for the dogs and birds."
As the tale develops, however, man's mortality becomes the state through which he may demonstrate sacrifice, courage, and heroism. Hector refuses to remain within the safety of the gates of Troy, despite the desperate pleadings of his wife and parents who fear his death. Achilles welcomes fighting to his own death, feeling deep guilt over the loss of his dear friend Patroclus. Priam faces death to bring home his son Hector's body. These characters are willing to sacrifice their own mortality, with courage, for a good they deem greater than their own lives.
Throughout the poem, man's mortality is explored in terms of the capriciousness of the gods who intervene in human affairs. Humans live or die as the gods determine, and the power of Zeus is supreme:
. . . Father Zeus held out his sacred golden scales:
in them he placed two fates of death that lays men low--
one for Achilles, one for Hector breaker of horses--
and gripping the beam mid-half the Father raised it high
and down went Hector's day of doom, dragging him down
to the strong House of Death--
The Iliad develops the idea that human beings are mortal, their deaths determined by immortal gods; how they face death, however, is a matter of free will. Human beings may choose to be heroic.