At an academic conference a few years ago, I met a bishop from a Catholic diocese in the Middle East. The bishop reflected on meeting local Muslim leaders just after his appointment. They were polite, he said, but not especially warm, as they suspected Christianity as a foreign influence. Still, they allowed that they were pleased the Church had sent them an actual Arab. “At least they managed to find us one of our own,” they said.

The bishop laughed as he told this story. The Church had “managed to find” an Arab Christian? It shouldn’t have been a surprise. Christianity was born in the Middle East, and the bishop’s ancestors, all Christians, had lived there for centuries. He himself had been born and raised in the country to which the Church had assigned him. But, in the last 100 years, the Christian population of the Middle East has shrunk dramatically, a consequence of genocide and mass emigration. Increasingly, people find it hard to remember that sizable Christian communities ever existed in the region.

In his valuable new book, Heirs to Forgotten Kingdoms, Gerard Russell describes some of these Christian communities, along with several other religious minorities that somehow have managed to endure in the Middle East. The book is part history and part travelogue. Russell worked for a decade in the region as a British and U.N. diplomat and speaks fluent Arabic and Afghan Persian. He spent four years researching the book. As a result, he speaks with an authority that outsiders often lack. And he does so in an engaging manner, with insight, humor, sympathy, and admiration for the groups he describes.

In addition to Coptic Christians in Egypt and Chaldean Christians in Iraq, Russell describes six such groups. There are the Mandaeans in southern Iraq, who reject Abraham but follow John the Baptist—a much greater miracle-worker than Jesus, they say. There are the Yazidis of northern Iraq, about whom most Americans first learned last summer, when ISIS militants trapped a group of them on Mount Sinjar. Yazidis revere an angel they call Melek Taoos, the Peacock Angel. This angel once rebelled against God, they say, but eventually repented and received forgiveness. Muslims see a similarity with the evil angel of Islamic tradition, Iblis, and accuse Yazidis of devil-worship. The Druze in Lebanon believe in reincarnation and the Universal Mind. Russell argues that they carry forward the religion of Pythagoras.

Another chapter describes the Zoroastrians, who maintain the ancient religion of the Persian Empire, a monotheistic, dualist faith centered on a divinity called Ahura Mazda. In Pakistan, Russell spends time among the Kalasha, the last pagan tribe that remains in the country, the descendants, perhaps, of Alexander the Great’s soldiers. Most interesting, for Christians, is his visit to the Samaritans, who still worship on Mount Gerazim in Israel, a practice Jesus himself discussed with the Samaritan woman at the well.

Three themes unite Russell’s treatment of these groups. First, there is the blunt fact of their survival over centuries in an often hostile environment. In part, Russell credits their longevity to a tradition in Islam of comparative tolerance. No equivalent faiths survived in Christian Europe, he notes. But it would be a distortion to ascribe their endurance wholly to Islamic open-mindedness. After all, these groups survived for centuries under Byzantium as well, and no one writes about Byzantine religious toleration. Although Islam often left these groups alone for decades at a time, they all suffered periodic, and brutal, repression.

These groups survived, as Russell himself makes clear, principally for two reasons. First, they hid—both literally and figuratively. They typically chose to live in remote regions (Mandaeans in the marshes and Druze in the mountains, for example) where central governments found it difficult to reach them. The persecution these groups suffer in modern times, Russell suggests, may simply reflect the fact that it is much harder for them to hide nowadays. And they kept their religious beliefs a secret from outsiders, sometimes even from lay practitioners. With the exception of Christians—more on this in a moment—these are esoteric, mystery religions. Only Yazidi sheikhs, for example, are allowed to know the faith’s “inner messages.” There is no catechism and no publicly available sacred text.

Second, the groups have shown a remarkable steadfastness in their faith. “The communities in this book have refused every inducement to abandon their religious beliefs and customs,” Russell writes, “and have often endured insult or violence in order to stand by them.” (They sometimes endure well-meaning, but nonetheless condescending, treatment today. The leader of the Samaritans reflects on the fact that their Passover celebration on Mount Gerazim has become a huge tourist attraction: “I don’t like to be an exotic, but that’s how it is. Anyone keeping a tradition is exotic.”) Their beliefs are precious to them in a way many people in the West no longer appreciate. And they have held fast to their identities, which are typically communal as well as religious. One does not believe in the Druze religion, for example. One is a Druze. Intermarriage, for all these groups, is a grave offense.

Another of Russell’s themes is the link to antiquity. Time and again, he notes how these groups have maintained practices and beliefs from the pre-Abrahamic, pagan world. I have already mentioned the connections he sees between the Druze and the followers of Pythagoras. He finds echoes of ancient Babylonian religion in the Mandaeans, as well as commonalities with the Manichees. Aspects of the Yazidi faith remind him of ancient Mithraism. In the chants of the Coptic liturgy, he writes, one can still hear the music of the Pharaohs. Sometimes these links seem a bit forced, as when he discusses the similarities between Coptic monasteries and ancient Egyptian temples, right down to the sort of perforated bread they give visitors. But his insights are interesting.

Finally, there is the theme of displacement and the question of what happens now. Because of recent persecution, many members of these communities have emigrated to the West. More than 90 percent of Mandaeans have left Iraq since 2003, for example. There is a community of Yazidis in Lincoln, Nebraska.

Will these communities survive in their new environments? Russell hopes so. He describes some touching examples of endurance, like the time he heard a clerk speaking Aramaic in a supermarket in suburban Detroit. But he wonders how long it can last. For all its great achievements, America has a way of destroying traditional identities, and it’s difficult to maintain one’s distinctive customs for very long. He wonders whether escape to the West isn’t “a back-loaded contract for immigrant communities—get the benefit of prosperity now, pay the loss of identity later.” Still, it beats annihilation, which is what threatens these groups at home.

There is one problematic aspect of the book, and that is the way Russell groups Christians together with these other communities. It’s true that, like the Yazidis and the other communities he describes, Christians are not Muslims. But, in all other respects, their histories and present realities differ greatly.

Take the Copts, for example. At a conservative estimate, they make up 10 percent of the Egyptian population. That’s more than eight million people. How can one compare their situation to that of the 4,000 Kalashas in Pakistan, or the 750 remaining Samaritans in the world today? Moreover, Copts are hardly an esoteric religion. They may have a different calendar from other churches and an unfamiliar fasting discipline, but they have been an important part of Christian history from the beginning. Both St. Anthony, the founder of Christian monasticism, and St. Athanasius, the great defender of Nicene orthodoxy, were Copts. And, notwithstanding some theological differences with Western Christians, they are recognizably part of the Christian world today.

There is a danger in treating Copts and other Middle Eastern Christians like this. A major obstacle to getting American Christians interested in the plight of Middle Eastern Christians is the fact that they seem so foreign, so distant from the lived experience of Christianity in the United States. Accounts like Russell’s inadvertently emphasize the “otherness” of Middle Eastern Christians, thereby making it even less likely that they will draw the attention of Americans in a position to help. Of course, this is not Russell’s intention. As I say, he has genuine sympathy and admiration for all these groups, including the Christians. But his portrayal of them may have an unintended and unfortunate effect.

Nonetheless, this is an enjoyable and valuable book, instructive and a pleasure to read. It should appeal to anyone with an interest in the history of religion and the Middle East—indeed, anyone with an interest in the human spirit itself.