First off, to cast her with Eva Green is an insult in itself, because Artemisia was fucking badass. By the time I first learned of her in a battered book of my fathers about sea battles I was ten or eleven and really frustrated by the fact that there seemed to be no women in history I could identify with. And there she was, finally a woman where the book didn't say if she was beautiful or not, because for once it didn't matter. A woman, who was not just some cunning, seductive, or maybe wise queen, who sat back and let men have all the fun. There she was, a woman who was a fleet admiral in fricking ancient greece!
Not that I blame a 300 movie for historical inaccuracy (I mean, the persian king is a Goa'Uld and commands trolls) but that was plain character assaniation of one of history's coolest female heroes and my personal idol as kid, so I feel kinda compelled to put some things right:
Artemisia was the queen of Halikarnassos, a greek city. Je joined forces with Xerxes when he invaded, same as several other greek kings and queens did (no contrived rape plot needed). She commanded her own flottilla of about 5-100 ships (sources say different things, but certainly not the whole persian fleet). When Themistokles drew the persians into the gulf of Salamis, she was the only admiral brave enough to tell Xerxes that it was completely idiotic to go in there, because the strenght of their numbers and bigger ships would be a disadvantage in the straits of Salamis.
They went in there against her advice (not her jumping right into the trap like in the movie). She went in there and was said to be an extremely skilled admiral, although she did bend the rules somewhat. She had to sets of flags aboard and put up the greek ones whenever she needed to get past the greek ships and the persian one when she killed them. She realised quickly that she had been completely right about the straits and rescued what ships she could. On her way out of the fray she met her archenemy king Clamasitymus of Kalynda (also sayling with Xerxes) and used the good opportunity to sink him. Xerxes didn't hold it against her, since she was the only one who brought some ships back to him and had been right in the first place (she actually is famous for NOT having died there).
This was one smart and badass woman and she would have made one hell of a villain but what that movie did to her was an insult from start to finish!
And while we are at it Xerxes didn't really hold grudges much, because when the greeks then used Themistokles as massive skapegoat for everything that was destroyed in the war and he had to flee Athens, guess who hired him?
And as an add on:
From Herodotus' History:
"Of the other lower officers I shall make no mention, since no necessity is laid on me; but I must speak of a certain leader named Artemisia, whose participation in the attack upon Greece, notwithstanding that she was a woman, moves my special wonder. She had obtained the sovereign power after the death of her husband; and, though she had now a son grown up, yet her brave spirit and manly daring sent her forth to the war, when no need required her to adventure. Her name, as I said, was Artemisia, and she was the daughter of Lygdamis; by race she was on his side a Halicarnassian, though by her mother a Cretan.
"She ruled over the Halicarnassians, the men of Cos, of Nisyrus, and of Calydna; and the five triremes which she furnished to the Persians were, next to the Sidonian, the most famous ships in the fleet. She likewise gave to Xerxes sounder counsel than any of his other allies. Now the cities over which I have mentioned that she bore sway were one and all Dorian; for the Halicarnassians were colonists from Troezen, while the remainder were from Epidaurus. Thus much concerning the sea-force."
*steps of soapbox*