The Judgement of Paris is a very popular myth that explains the start of The Trojan War. There are different variations of the story, but this is the most common.
On Mt. Olympus
The Judgement of Paris story starts on Mt. Olympus when all the gods were gathered for a wedding. All of the important gods were there, except for Eris, the god of mischief and discord. She was excluded because nobody wanted mischief at a wedding ceremony. To get revenge, Eris wrote To the Fairest on a golden apple. She threw the apple in the direction of Hera, Athena, and Aphrodite. She ran away laughing, knowing there would be trouble.
When Hera saw the golden apple, she started bragging that it was for her. Athena quickly took it away, saying that the fairest meant the smartest. Aphrodite got mad, so she took it. She thought the fairest meant the most beautiful. The three female gods got into a big fight. They decided to go and ask Zeus who was the fairest. Zeus couldn't decide, because Hera was his wife. Zeus told them that the mortal prince, Paris of Troy, would decide.
Hermes first brought the three goddesses to bathe, then the three gods came down to earth to talk to Paris. Zeus had told Paris he could have them do any thing to help him decide. They all asked him who was the fairest. Since he couldn't decide, Paris put them through a series of tests and help him choose the winner. With no clear winner, the goddesses decided to bribe him. Hera went first, offering him the gift of power over Europe and Asia, riches and many victories. Next came Athena. She offered him the gift of wisdom, almost as much as her own. She said her would have a great mind for strategy and that he would be victorious in most all battles. Aphrodite came last. She said if he picked her, he could have the most beautiful girl in the world, Helen of Sparta. Although both Paris and Helen were married, he didn't need or want wisdom or power. He picked Aphrodite.
Paris came to visit Helen and her husband King Menelaus. They welcomed him warmly because at the time Troy was at peace with Greece. Aphrodite put her magic belt on Paris so that he would be irresistible to Helen. She instantly fell in love when she saw him. To Paris's happiness, Menelaus found out his father died and traveled to a different island. During the night Paris took Helen away to the walled city of Troy.
When Menelaus heard of his wife's kidnapping, he was enraged. He called all of the kings of Greece to help attack Troy. They built many ships, and over time, they were ready. The Judgment of Paris started the Trojan War.