While making this exact face.
Just ... Scottish Spartans? How does THAT work?
You know where else can you find Scottish Spartans? English translations of Greek plays. You're going to learn a little about translation theory, so go ahead and give yourself a preemptive wedgie.
Dynamic equivalence is the idea that you shouldn't translate stuff literally but rather in such a way that will cause the same reaction in the mind of the translation recipient as it would with the recipient of the original text. You've probably heard the Polish word kurwa, which means "bitch" or "slut" but is used much in the same way as Americans use "fuck," i.e. as everything from a noun to adjective to interjection. That's why the famous "fuck" scene in Boondock Saints was translated into Polish using kurwa instead of the straight translation of the word "fuck" (pierdolic/jebac). That's dynamic equivalence.
Warner Bros. Pictures
So, a century or so back, when English dudes were translating Greek theater plays and came across lines written in the Spartan variant of Greek, they looked for a dialect that English people would perceive the same way Athenians perceived Spartan Greek. That is, a dialect spoken by battle-obsessed madmen. It didn't take them long to decide to write all the Spartan lines in Scottish English after making sure no crazy Scottish person heard them calling Scots crazy. (If you tried to do the same thing with American English, you'd probably give Spartans Texan accents.)
Check out one such Scottish-Spartan translation of Aristophanes' Lysistrata:
"Assess them, ye tickler, wi' such tender chucks I feel as if I were an altar-victim."
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"And throw ye another haggis on the barbie."
In light of this, it makes perfect sense that 300 is a filmed STAGE ADAPTATION of the Thermopylae story. It would explain the lead's Scottish accent, the exaggerated violence, and the almost theatrical production values. Keep in mind, though, that this would be the kind of theater production where the first two rows receive free plastic tarps due to all the flying bro sweat.
Plus, at the end of 300, it turns out that the entire story was told by one of Leonidas' soldiers. That character is clearly acting as the choragus, the leader of the chorus in Greek theater who narrates the story and sometimes even inserts himself into it. This effectively makes 300 the second secretly theatrical pop culture staple after Super Mario Bros. 3.