The found manuscript trope

 I was thinking of this with the Quijote, which purports to be a translation of a found manuscript written in Arabic.  Where did this trope come from? Was Cervantes the first to use it?

Well, it is actually a feature of the novels Cervantes was parodying, like Amadís de Gaula. I should have thought of this first. But, by parodying this trope, rather than using it in earnest, Cervantes was the first in using it to highlight rather than diminish fictionality. His is the first metafictional use of the device, then. 

I'm probably wrong about this, since I haven't read Amadís.