in the first line of the iliad what is the iliad about

The Iliad begins with the Trojan War already in progress. Greek audiences would have been familiar with the background of the story, and here a brief summary of events is necessary to help the reader to put these events in context,

"Sing, O goddess, the anger of Achilles son of Peleus, that brought countless ills upon the Achaeans. Many a brave soul did it send hurrying down to Hades, and many a hero did it yield a prey to dogs and vultures, for so were the counsels of Jove fulfilled from the day on which the son of Atreus, king of men, and great Achilles, first fell out with one another. "