After the events of the Iliad and the death of Hector, the Trojan War still wasn't over. Neither the Greeks nor the Trojans seemed to be able to win, until one of the Greek kings, Odysseus of Ithaca, had an idea.
"Build a big wooden horse on wheels," he said, "big enough for a bunch of Greek soldiers to hide inside it." So the Greeks did. Then the Greeks all pretended to sail home (except the ones hiding inside the horse!). They acted like they had given up and left. But really they hid just around the corner.

Soon the Trojans found the horse. "What is it?" they asked each other. Nobody knew. (The Greek soldiers hiding inside kept very quiet). Then they found a Greek soldier hiding nearby. He said (though this was part of the trick) that the other Greeks hated him and they had left him behind. So the Trojans asked him what the horse was for. He said it was an offering to Athena.

Well, the Trojans didn't want to upset Athena either, so they rolled the big horse into the city of Troy. It was so big it wouldn't go through the gate, and they had to tear down a piece of the city wall to get it in. They left it at the temple of Athena, and then  the Trojans had a big party to celebrate the end of the war. (Still the Greek solder inside the horse kept very quiet).

Finally everyone fell asleep, and NOW the Greek soldiers came out of the Trojan Horse and killed the guards on the walls. They signalled to the other Greeks to come attack Troy. They could get in now because the walls were torn down. There was a big battle and the Greeks won. All the Trojan men were killed, and all the women and children were taken back to Greece as slaves.