Much of the content of the "Iliad" is very much the same, and without a special device such as the one used by Homer, the story would be completely mundane. This special literary device that Homer elevates from a simple artifice to an invaluable benefit to his work is the simple metaphor.
A metaphor is known usually as just a simple use of language to take one object and compare it to another object--however not in the same was as a simile. Homer does however also use similes, and his ability to combine an expert use of simile and metaphor enable him to create a work definetely worth reading.
The following example shows how Homer uses similes to ilicit the action of his ancient tale.
"The two immortals stepped briskly as wild doves,
quivering, keen to defend the fighting men of Argos."
-Fagles, Iliad 189.896-'7
Overall Homer's use of simile and metaphor adds brilliant and vibrant life to this epic poem that simply wouldn't have it without this great addition.