I’m pretty sure Dante Alighieri was not writing fanfiction, but was in fact creating a satirical work, as he wrote this during his years of being Excommunicated. Which is also part of The reason it’s referred to as The Divine Comedy (La Divina Commedia). He was excommunicated for false political crimes.

Also Dante’s Inferno was also a proof of concept for what became the modern Italian language.

( though if you’re saying fan fiction sarcastically I do agree)