Thermopylae was a location on Earth most famous for being the location of the Battle of Thermopylae in 480 BCE. This was a mountain path by the sea, where the Sparta leader Leonidas I, three hundred Spartans, seven hundred Thespians, four hundred Thebans, and nine hundred Helots defended the pass from the Persians.

At this time, Vulcan was consumed by many minor wars. (TOS novel: The Romulan Way)

In 2375, Julian Bashir had a holoprogram featuring the battle and he and Ezri Dax planned to defend the pass. (DS9 episode: "What You Leave Behind")