Thoughts provoked by the Iliad

I'm plowing through Homer's Iliad. Well, actually I'm only in Book 3, but it feels like I'm plowing through it. As I read it, though, I'm reminded by what Bernard Knox said in the Introduction of this volume - that the Greeks in Homer's day had no conception of the after-life being granted to mortals. Immortal deities were lucky to have everlasting existence, but mere mortals died and then retired to an eternal, black sleep. (In this context, Knox comments on the cruelty and capriciousness of the Greek gods, who in intervening in the lives of people and in many cases causing needless suffering and death, they lacked any sense of decent morality given that they did not have to die and be vanquished for all eternity.) I was wondering, however, if this view that death was the end, without afterlife, was true for the Greeks throughout their history, or if it was true only for Homer's age. It seems that I have read that the after life was commented on by later Greek philosophers.