that question has been around for a very very long time...and while not stated in the film, it underlies a lot in the movie.
One word in advance: this is not a historical Persia...this is more the sort of Persia you might find on Riverworld, where people from all parts of history have gathered: Prince Dustan's adopted father, in addition to being the King of Persia (King of Kings), but he also broke the power of the Assassins - which would mean he is also the Great Khaan.
Arabic script exists alongside main characters speaking of "the gods"* in an empire big enough to make Xerxes envious.
(not sure if anyone ever did ostrich racing, though)
There's more than a few light-skinned people in this movie...but at least this time the casting people tried to get actors who looked like they came from Spain, North Africa, and the Mediterranean and Turkish/Iranian Plateaus.
(most unlike, say, Gladiator, where all the Senators, Emperors, and centurions looked like they had just left Scotland)
There's talk of gods and greater powers here...but unlike Clash of the Titans, there is no divine interventions.
Gemma Arterton does a splendid job portraying the Princess Tamina.
* = And that was said by the Princess of Alamut...which historically was one of the two power bases for the Assassins - but not here.
though they do show us a hint that Alamut and the Assassins do have a connection.
Interestingly, unlike most movies, Prince Of Persia has no Big Huge Fight Scene[tm] near the end. There's lots of fights and battles during the film...but it is more like chess: positioning of the pieces towards your goal. (and I liked how they did this)
Though, at the end, I'm left wondering...how much will Dustan tell his brothers of what just happened? And how much will he tell anyone else?
this could be crossovered with almost anything -
- Primeval (the stone of the dagger looks anomalyish)
- Supernatural (the sands of time could be more dangerous than the Colt, the archangels...a definate game-changer)
- Highlander (whether this is the future or the past, one can picture Immortals easily in this realm)
and before I forget..."Did I ever tell you about the Mbaka?"