"The Battle of Thermopylae" is intended as the alternate for questions which might have "Tau is exactly six" as the answer.

For example: "What would be one consequence of a new state law which defines the ratio of a circle's circumference to diameter as exactly three?"

I bet that you can't write a question for which "Tau is exactly six." and "The battle of Thermopylae" are both answers which gain any credit...