In 2007 I took a short train ride from Baku to see one of the few remaining Zoroastrian fire temples, the Ateshgah. Inside a compound that shuts out industrial suburbs on one side and nodding donkeys in the semi-desert on the other, a stone pavilion sheltered a bobbing sacred flame. My impression of an ancient faith assailed by modernity grew stronger later when, in a room on the perimeter of the precinct, I came across a gas meter. 

A red reminder must rank low among the Zoroastrians’ worries: their relations with their Muslim neighbours are tense. As Gerard Russell explains in this absorbing and thought-provoking book, they, and six other extraordinary religions he encountered during fourteen years’ diplomatic service, are ‘more vulnerable than ever’.

Traditions including secrecy and bans on marrying outside the faith partly explain this. But the widespread sectarianism unleashed by the invasion of Iraq in 2003 has made matters much worse. The Yazidis became infamous this summer when they were encircled by ISIS’s hordes. Their refusal to eat lettuce or wear blue is odd. But it is their reverence for an angel like a peacock that has led to accusations of devil worship, which the extremists then use to justify rape and enslavement. It is a misunderstanding Russell investigates and then debunks.

In southern Iraq the Mandaeans, who follow John the Baptist, have lived in the marshes for at least 1,500 years. Since 2003, nine out of ten of them have fled or been killed. In the tragicomic opening to the book, Russell recounts the moment when, during his posting in Iraq, ‘In the faded cafeteria of Baghdad’s al-Rashid Hotel, the Mandaean high priest, his brother and his cousin all looked at me, asking for my help.’ It was, he writes, ‘like being summoned to meet one of the Knights of the Round Table, or discovering that in a small village in the English countryside a community still worshipped Odin and had invited me to tea’. The surprise was that the Mandaeans still existed at all.

Russell argues that this survival has been partly due to sophistication. The religions that emerged in Mesopotamia were influenced by ideas from far-flung parts of the Persian and Roman empires that vied to dominate this continental crossroads. One vital cross-fertilisation took place in the sixth century BC when, during the Babylonian captivity, the Jews absorbed the Zoroastrian belief that good conduct would lead to eternal life. But the real period of flux occurred in the early Christian era. While the rulers of Byzantium rejected their classical heritage and tried to impose Christian orthodoxy, thinkers in the highly urbanised Levant coopted Greek philosophers such as Plato and Pythagoras in an attempt to resolve two vexing questions: why, if God was omnipotent, did evil exist, and could the powerful human mind outlast the vulnerable body?

Many came up with answers. Mani, who counted St Augustine among his followers for a time, thought he could free the spirit through strict asceticism, while the Sufi mystic Hussein ibn Mansour al-Hallaj argued that Satan had refused to bow to Adam only because of his uncompromising love of God. Although the early Islamic rulers were surprisingly tolerant of such inventiveness, al-Hallaj was executed after declaring that he himself was God. What if one of these early thinkers had prevailed?

In this book – part vivid odyssey, part lucid history – Russell aims to show us how much we have in common with these vestigial faiths, and what they share with one another. Besides the Mandaean high priest he meets Yazidi elders, Druze warlords and Copts in Kensington in his patient quest to understand precisely what they believe. With a nicely judged amount of detail, he sets out world-views that are both familiar and foreign. Christians and Muslims would nod along to the Mandaeans’ declaration of faith in one God; but the Mandaeans are also keen astrologers who believe that children who die unbaptised are comforted for eternity by trees bearing breast-shaped fruit. The Nabataeans beg mercy from the Lord of Heaven before launching into a recipe for forgiveness that requires handfuls of dead bats and rats. The Yazidis paint eggs for New Year but they also sacrifice young bulls – just as the Assyrians did before them in the same part of the world.

Then there are the kaleidoscopic links between religions. The Druze and the Yazidis, for instance, are at one on the importance of moustaches. Their belief in reincarnation and reverence for the Greek philosophers are shared by the Alawites, whose view of the importance of wine in helping them commune with God is also held by the Zoroastrians. Incidentally, the importance of wine and philosophers to Zoroastrianism explains why Ayatollah Khomeini studied Plato and once wrote a poem containing the unlikely line, ‘Let the doors of the tavern be opened and let us go there day and night.’

One tangible inheritance from this world is the handshake, which might have remained a conspiratorial gesture used by the Yazidis and their neighbours the Mithraists had Mithraism not then achieved cult status within the Roman army. To establish themselves as ‘brothers in the afterlife’, Yazidi men place a ball of moistened soil from their shrine at Lalish between their palms as they shake. Russell met two such ‘brothers’ after they had claimed asylum in North America. They told him how a Jordanian customs officer had laughed and confiscated the soil they intended to bring with them on their exodus. There are more terrible stories in this book, but I found this moment the most affecting of all.

In one sense Heirs to Forgotten Kingdoms treads a well-worn path. As Russell admits, British writers have been forecasting these esoteric remnants’ imminent disappearance for at least three centuries. But today, as their last adherents face fanatical persecution at home or dispersal in exile, the future looks undeniably grim. Gerard Russell’s timely and humane depiction of them is a compelling read.