The Battle of Thermopylae was a famous battle of the Persian War in the history of Earth.
In the year 480 BC, King Leonidas led his 300 Spartans, and 7,000 Greek allies in the defense of a mountain pass at Thermopylae, against an invading Persian army of perhaps 200,000. At the climax of the battle, the Spartans and 600 remaining Thespians fought to their deaths against the Persians, inflicting such casualties that it gave the Greek city-states enough time to organize and eventually defeat the invaders.
Julian Bashir invited Ezri Dax to experience the battle with him in 2375, after his long-time holodeck companion Miles O'Brien left Deep Space 9.
When Ezri discovered the battle had a theme ("Fighting to the last man!") similar to the Battle of the Alamo, and they were going to be the Spartans, she asked , "Have you ever talked to a counselor about these annihilation fantasies?" (DS9: "What You Leave Behind")