Explanation: The Late Roman Empire, whose soldiers are depicted here, was Christian.
Some Christian sects fast (generally only from specific foods, like meat) during Lent, the lead-up to Easter.
"So hungry I could eat a hippo/horse/other large animal" is a common English idiom simply meaning one is very hungry.
Augustine of Hippo was a Christian theologian of the period.
Fellow hungers for the wrong Hippo