Zoroastrianism is one of the world's great ancient religions. In present-day Iran, significant communities of Zoroastrians (who take their name from the founder of the faith, the remarkable religious reformer Zoroaster) still practise the rituals and teach the moral precepts that once undergirded the officially state-sanctioned faith of the mighty Sasanian empire. Beyond Iran, the Zoroastrian disapora is significant especially in India, where the Gujarati-speaking community of emigrants from post-Sasanian Iran call themselves 'Parsis'. But there are also significant Zoroastrian communities to...