Persian it is. Cos half of the Arab conquests consisted of lands formerly making up the Persian Sassanid empire. Had the Byzantines and Persians not fought so many wars and wearied themselves over the 2-3 preceding centuries, the Arabs would probably not be so successful. The illiterate Arabs weren't administrators so they got their Persian subjects to do all the bureaucratic work, so eventually Persian came to such importance.
Anyone's welcomed to the next question......
Anyone's welcomed to the next question......
