There's one iron-clad rule of pseudo-historical action roleplaying. You do not kill the messenger. By "iron-clad", we mean of course that everybody and his dog breaks it - but only with dire consequences.
So sending in a messenger is almost guaranteed to be a good way to get your players arguing, leading inevitably to the aforementioned dire consequences, which you can then honestly blame on the actions of the PCs and not on any deception or foul tactics on your part.*
* In the sense that you did actually use deception and foul tactics, of course.
In the real world of the Sandals & Spartans universe, of course, the 300 movie doesn't exist. That's the premise of this entire comic, after all. But most of the other things we know and love (such as testosterone-overloaded battle scenes) do, albeit modified by the lack of 300:
- Greekballs is a serious documentary about keftedes.
- Gerard Butler is known (barely) for doing voiceovers for poorly selling computer games, but gains widespread fame after his appearance in the first Futurama movie.
- Dominic West is known primarily for his role in Spice World.
- Nerdy guys make YouTube videos of themselves sword fighting in Renaissance era costumes instead of bare chested.
- Without the success of 300 to spark interest in historical epics, Xena, Warrior Princess was never revived with a movie and a new series, and remains an obscure short-running TV show.
- The Odyssey was never made into a film. Greek mythology fans never had it so good.
- The major historical epic background that pervades all of Western culture is Ben Hur, despite it never being much good. The original film was remade recently into a new, updated television series with a bigger budget, high-tech computerised special effects, and edgy writing. And it sucked.
- Throughout the 90s and 2000s, all the greatest Hollywood blockbusters were big-budget psychological thrillers.
- The Comic Irregulars exist and are making a screencap comic based on Avatar.
Stelios: Oh, we are in so much trouble.
King Leonidas: It's just a misunderstanding.
Stelios: You killed their messenger!
King Leonidas: He was an assassin! The spaghetti was poisoned.
Stelios: I don't think the Persians had spaghetti.
King Leonidas: IT. WAS. PASTA!
Captain Artemis: Relax. With my battle plan and terrain advantage, 300 level 1 fighters is enough to hold off an indefinite number of minions.
King Leonidas: I'll talk to Circus again.
King Leonidas: He should see reason when I explain to him what happened.
King Leonidas: I'm a skilled diplomat!
Captain Artemis: According to my calculations, we'll take 299 casualties. The remaining fighter will have levelled up enough times to be practically invincible.
King Leonidas: Hey, I already talked him into letting us fight in the shade!