How does the author use foreshadowing in The Pharsalia?

The remarkable naumachia of Book 3 has a specific function: it is the inevitable consequence of sacrilege, but, as Caesar departs for Spain before it takes place, it is a substitute for the real struggle, a metaphor which foreshadows that struggle and conveys further just what Lucan, and the Massiliotes, mean when they speak of "sacred wounds."