Rubaiyat/Omar Khayyam.
This movie is a complete fiction - nothing is known about Omar Khayyam's life. In fact, it is not even known with certainty whether or not he composed the verses he used in the movie (or rather, the actor playing him used). Also, the producers seem to have forgotten a little about Arabian history:
1. The assassin sect was called the "Thuggee," not the "Assassins."
2. The rulers of Persia at this time were what is now called "Moogol," that is, they were part Mongol, part African, and part Arabic.
3. It is not known what went into the "Greek fire."
4. It is unlikely the Romans could have invaded so far into Persia.
5. After the Sultan's death, the Queens would shave off their hair, put on the white robes of a penitent, and leave the Sultan's house forever; alternatively, they could choose to die with the Sultan through the rite of suttee - they would be placed on the burning pyre along with their husband's body. (As seen in Jules Verne's famous novel, some women were forced into an act of suttee against their will.)
6. The Thuggees killed both men, women and children.
7. Omar composed his calendar with the aid of seven other scholars, and it was the sultan's desire that he do so, to do away with the old calendar.