I was thinking this while reading The Canterbury Tales, which isn’t exactly the oldest I’ve read (I think that goes to Homer)
But The Canterbury Tales is just so delightful! Getting into the flow of the rhyming prose is very fun to read (I’ve just been reading the Penguin Classics Coghill translation which is fantastic)
I’ve already watched the Pasolini adaptation but I’m definitely going to revisit once I finish the book.
Since someone already said Beowulf, I’ll go a bit later and say Le Morte D’Arthur. The Song of Roland is also really good.