In the third book of Vergil's Aeneid, Aeneas has landed in the land of Chaonia, which is in northwestern Greece. There, he discovers Andromache, the former wife of Trojan Hector, and her new husband, Helenus, who had also been a Trojan. Andromache and Helenus are now queen and king of a land that looks like a smaller version of Troy.
Helenus was also a prophet of Apollo and he gives Aeneas a sign by which Aeneas will know that he has reached the goal of his journey (Italy).
When, in your distress, you find a huge sow lying on the shore,
by the waters of a remote river, under the oak trees,
that has farrowed a litter of thirty young, a white sow,
lying on the ground, with white piglets round her teats,
that place shall be your city, there’s true rest from your labours. (A.S. Kline translation)
Indeed, Helenus' prophecy comes true. It is repeated in Aeneid 8 by the god of the Tiber river, who appears in a dream to Aeneas. The next day, Aeneas sees the predicted sow and her litter of baby pigs.