Scholars once doubted that pre-literate peoples could ever have composed and recited poems as long as the Odyssey. Milman Parry changed that.
>> “Instead of construing the Iliad and the Odyssey as either conventionally authored works or pieced-together editions, Milman Parry portrayed them as the products of a generations-long process of composition in performance,” Foley wrote. This helped revolutionize the way we understand the oral origins of epic poetry.
https://daily.jstor.org/how-do-we-know-that-epic-poems-were-recited-from-memory