In the Trojan War legend, the Trojan priest Laocoön warned that the Greeks’ wooden horse was dangerous.
After the Greek army appeared to sail away, it left the horse outside Troy. Laocoön urged the Trojans not to trust the apparent offering and is associated with the warning, “I fear the Greeks, even when bearing gifts.” In Virgil’s Aeneid, he specifically argues that the horse may conceal Greek soldiers.
The warning fails because sea serpents attack Laocoön and his sons. The Trojans interpret this horrifying event as a divine punishment for opposing the horse, so they bring it inside the city. Greek soldiers hidden within later emerge and open Troy’s gates.
The exact details differ among ancient sources. The Laocoön episode is especially famous through Virgil’s Aeneid and the ancient sculpture known as the Laocoön Group. The story is also the source of the modern phrase about fearing gifts from an enemy.