Trojan Horse

Paris, a prince of Troy, took Helen, the wife of Menelaus to be his wife.  This naturally enraged Menelaus, who then strove to reclaim his wife.  This started a war between the Trojans and the Greeks.

In trying to penetrate the city of Troy, Odysseus came up with a brilliant idea.  (Some claim it was with the help of the Goddess Athena.)  A wooden horse was built.  Some of the elite of the Greek army hid in its belly.  The rest of the army dragged the horse to the wall of the city, and then sailed away.

The Trojans thought that the Greeks had sailed away, leaving the horse as a gift.  They wheeled the horse into the city.

Later, under the cover of night, the Greeks came out from the belly of the horse and opened the city gates.  This allowed the rest of the Greek army, who had sailed back, to go in and attack Troy in order to save Helen.

For more information:
http://www.stanford.edu/~plomio/history.html
http://en.wikipedia.org/wiki/Trojan_Horse