In Search of Zarathustra: the first prophet and the ideas that changed the world, by Paul Kriwaczek

He gave us monotheism - and Freddie Mercury

The Parsees are often likened to the Jews. From the Indian state of Gujarat, this small group of believers with its distinctive interest in fire-worship has spread into a worldwide diaspora, making notable contributions wherever they settled. In India, it was a Parsee who established the first printing press and the oldest newspaper and captained the first national cricket team. A Parsee was the first Indian undergraduate at Oxford, another the first English baronet of Indian origin, another the first Indian-born MP. On the modern roll of honour are the conductor Zubin Mehta and Freddie Mercury.

Parsees (meaning Persians) are the last remnant of Zoroastrianism, a religion that one dominated much of the Middle East and central Asia. As Paul Kriwaczek shows, it left more of a mark on Judaism, Christianity and Islam than any of this holy trinity would care to admit. The followers of the prophet Zoroastra or Zarathustra or Zarathushtra (depending on how close to the old Persian you want to get; it translates as "rich in camels") have been around since 1200BC. They enjoyed several peaks of influence, notably as the state religion under the Iranian-based Achaemenid empire, which stretched from the Nile to the Indus and from the Caucasus to the Arabian Sea until swept away by Alexander the Great in 330BC. However, they were reduced to a rump and exiled by the spread of Islam from the seventh century onwards.

Zoroastra's distinctive contribution was to teach of a single god, Ahura Mazda, rather than the crowded pantheons favoured by all other religions at the time. When the Jews were taken in captivity to Babylon in the sixth century BC, they came into contact with such beliefs and integrated them into their own credo and, ultimately, that of Christianity. Just as influential was Zoroastra's description of life on earth as a cosmic battle between Ahura Mazda and the fiendish Ahriman, the forerunner of the Christian Devil. The picture of a final confrontation, with salvation for the blessed and damnation for the wicked, predates all other accounts of a day of judgement.

Kriwaczek has hit upon a fascinating and neglected subject which, with his background as a BBC producer in the Middle East, he is well-equipped to illuminate. He faces several handicaps en route: the almost complete absence of historical evidence about Zoroastra; the wishy-washy paucity of the writings attributed to him; and the efforts of subsequent generations of Muslims to bury his memory. All of these he deals with manfully, taking his readers back to ancient times with imagination and style, moving deftly between the present, the recent past and the mists of time.

My main problem, though, is the overall route Kriwaczek takes. Starting at length with Nietzsche, whose Thus Spake Zarathustra in 1883 (a philosophical tract arguing against morality) brought the prophet to modern attention, he circles round and round his subject, clambering back though time. It is only in the final chapter that we find out exactly what can be known about Zoroastra from historical, archaeological and theological debate. That would have been my starting point. This is an upside-down book, which may sound a nice literary device but can be deeply frustrating.

The good in it wins through, however. Kriwaczek is particularly strong on the almost unconscious survival of elements of Zoroastrian belief in modern Iran. I especially liked his description of playing peeping Tom at the desert shrine of Yazd, where a flame has reputedly been burning since the year 470. He watches as Iranian women take off their shapeless black chadors (but keep on their headscarves) to reveal underneath their brightly coloured Zoroastrian costumes. They sing under the myrtle trees, in a joyous and informal celebration. As an image of the heterodox nature of belief in lands that we in the West caricature as religiously intolerant, this says it all.

The reviewer's 'Heaven: a traveller's guide' is published by HarperCollins next week