The Trojan Horse is a tale from the Trojan War about the stratagem that allowed the Greeks to finally enter the city of Troy and end the conflict. In the canonical version, after a fruitless 10-year siege, the Greeks constructed a huge wooden horse, and hid a select force of men inside. The Greeks pretended to sail away, and the Trojans pulled the horse into their city as a victory trophy. That night the Greek force crept out of the horse and opened the gates for the rest of the Greek army, which had sailed back under cover of night. The Greeks entered and destroyed the city of Troy, decisively ending the war.
The main ancient source for the story is the Aeneid of Virgil, a Latin epic poem from the time of Augustus. The event does not occur in Homer’s Iliad, which ends before the fall of the city, but is referred to in the Odyssey. In the Greek tradition, the horse is called the “Wooden Horse” (Δούρειος Ἵππος, Doúreios Híppos, in the Homeric Ionic dialect).
Metaphorically a “Trojan Horse” has come to mean any trick or stratagem that causes a target to invite a foe into a securely protected bastion or space. It is also associated with “malware” computer programs presented as useful or harmless to induce the user to install and run them.
According to Quintus Smyrnaeus, Odysseus came up with the idea of building a great wooden horse (the horse being the emblem of Troy), hiding an elite force inside, and fooling the Trojans into wheeling the horse into the city as a trophy. Under the leadership of Epeios, the Greeks built the wooden horse in three days. Odysseus’ plan called for one man to remain outside of the horse; he would act as though the Greeks abandoned him, leaving the horse as a gift for the Trojans. A Greek soldier named Sinon was the only volunteer for the role. Virgil describes the actual encounter between Sinon and the Trojans: Sinon successfully convinces the Trojans that he has been left behind and that the Greeks are gone. Sinon tells the Trojans that the Horse is an offering to the goddess Athena, meant to atone for the previous desecration of her temple at Troy by the Greeks, and ensure a safe journey home for the Greek fleet. The Horse was built on such a huge size to prevent the Trojans from taking the offering into their city, and thus garnering the favor of Athena for themselves.
While questioning Sinon, the Trojan priest Laocoön guesses the plot and warns the Trojans, in Virgil’s famous line “Timeo Danaos et dona ferentes” (I fear Greeks even those bearing gifts), which became known as ‘beware of Greeks bearing gifts,” Danaos being the ones who built the Trojan Horse. However, the god Poseidon sent two sea serpents to strangle him and his sons Antiphantes and Thymbraeus, before any Trojan believes his warning. According to Apollodorus, it was Apollo who sent the two serpents since Laocoon had insulted Apollo by sleeping with his wife in front of the “divine image”. Helen of Troy also guesses the plot and tries to trick and uncover the Greek men inside the horse by imitating the voices of their wives. Anticlus would have answered, but Odysseus shut his mouth with his hand. King Priam’s daughter Cassandra, the soothsayer of Troy, insists that the horse would be the downfall of the city and its royal family. She too is ignored, hence their doom and loss of the war.