Interesting thing I read about Homer. The Iliad and The Odyssey are very long pieces to memorise, and they did originate in a time before writing. One theory has it that they were actually songs.
I don't know about you, but I can sing along with the radio, with just about every song from the 60s to the 90s (after that I haven't enjoyed music so much, but the good songs do go in). That's a LOT of words to remember. I'm pretty sure there's a tie-in with memory and music, maybe something to do with rhythm or melody. Have a think about how many songs you know.