I know there were attempts at this by the Romans and Parthians. But, what if it actually took place? Obviously there would be lasting good will between the two powers. But, how long would it last and what benefits would we see? If it's before the Romans become Christian, would we see greater Zoroastrian influence on Roman religions (I don't think you can count Mithraism, because I don't see much Zoroastrian beliefs in that creed).