What is the oldest non-biographical work of literature in which the author is also a protagonist?

Question

Dante's Divine Comedy, written in the years 1308-1320, is a long narrative poem in which the poet is also a protagonist in the story. The story also includes many real characters, such as Virgil and many Florentines who had been involved in the struggle between the Guelphs and the Ghibellines. However, it is obviously not an autobiographical work, since Dante's journey through hell, purgatory and paradise is not a real event.

This leads me to the question whether the Divine Comedy is the earliest work of literature in which the author is also a protagonist in the story. This should not be confused with works in which the protagonist is the narrator but not the historical author; narrator and author are two different concepts. (I am also excluding philosophical dialogues from this question, otherwise Plato's dialogues might be a valid answer.)

Answer 1

As written, the most obvious answer would probably be a lyrical poet, writing in first person. Sappho's poetry (ca 600 BCE) appears to be among the first in the Western tradition to use such a device. To what degree it is biographical can of course be debated.

The first writing that is definitely fiction is probably Lucian of Samosata's A True Story, written in the second century CE. In it we can read about the fantastical travels of the narrator, who at one point erect a monument on which we can read that his name is "Lucian". He and his company travels beyond the Pillars of Hercules, are taken by a whirlwind to the Moon, witness a war between the forces of the Moon and those of the Sun, travel in the belly of a giant whale, go to the Islands of the Blessed and meet the heroes of the Trojan War. A True Story is often cited as the earliest science fiction novel, containing a lot of elements we recognize from modern offerings of the genre.