The Deep is a short early (1975) novel by John Crowley.
A visitor arrives from elsewhere on a mediaeval world. It soon becomes apparent that he (it) is only superfically human. Damaged in a skirmish between Protectors and the Just, he and we spend the rest of the book finding out how and why he was made and sent. Early on, Fauconred quotes their book to him, which says: "the world is founded on a pillar which is founded on the Deep". This turns out to be true.
Whilst a war of succession (apparently patterned on the Wars of the Roses) plays out, the visitor changes roles into secretary, then recorder; and travels to the edge of the world to meet Leviathan. Meanwhile, the slow stable world which has been "immortal" because repeating for uncounted years begins to spiral into the unknown path of development.
External links