Saying one thing through another, without a word of comparison: instead of saying that something is like another thing, one says that it is. The image transfers to the subject the qualities of the thing it has been identified with.
In the Aeneid
Why does it please you so much to surrender to this mad grief, sweet husband? This does not happen without the will of the gods; it is not lawful for you to take Creusa as your companion, nor does the lord of high Olympus permit it. Long exiles await you, and a vast sea to plough.
“a vast sea to plough” treats the crossing as farming: the boat opens the sea the way the plough opens the earth. The image makes exile a hard and long labor, not a simple journey.
Book II: The Fall of Troy, Creusa
No goddess is your mother, nor Dardanus the founder of your line, treacherous one; the bristling Caucasus bore you among hard crags, and Hyrcanian tigers gave you their breast.
What new madness is this? Where are you going now, where, he said, O wretched citizens? You are not burning an enemy or the hostile camp of the Argives: you are burning your own hopes. Here I am, your Ascanius.
We are broken, alas, by the fates, he said, and carried off by the storm. You yourselves will pay for these penalties with sacrilegious blood, you unhappy ones! For you, Turnus, the crime, for you the wretched punishment awaits; and with late vows you will worship the gods. For me, rest is assured, the whole harbor is at my door; I am deprived of a happy death.
Book VII: The Arrival in Latium, Latinus
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