The stark cliffs of the Zagros Mountains on the Iran-Iraq border, and the dusty hills and plains that lie between those mountains and the city of Mosul, might seem an unlikely location for paradise. Yet Christians living here in past centuries believed that a local river called the Great Zab had once flowed from Adam and Eve’s garden. Patriarchs of the Christian Assyrian Church of the East living on its banks once signed off their letters with the salutation, “From my cell by the river of Eden”.

These days the Patriarch’s letters are sent from a less romantic spot: 7201 North Ashland Boulevard, Chicago. Successive waves of persecution have driven out the leaders of this ancient, prestigious and little-known church—including Mar Dinkha IV, the present and 120th Patriarch of Babylon, who was consecrated in Ealing, west London, and is based in the United States. As for the Great Zab, this summer it ended up as the de facto border between Kurdish forces on its southern side and the so-called Islamic State (IS) to its north. From being the garden of Adam and Eve, Iraq has become the land of Cain and Abel. Yet even its melancholy recent history can remind us that the religious conflict that scars the modern Middle East is far from inevitable.

In 1987, Christians in Iraq numbered 1.4 million. Since then, the country’s population has doubled but its Christian community has declined to 400,000. Many of these people are now internally displaced because of IS, a Sunni Muslim militant movement that drove them from their homes in August 2014 in its effort to establish an Islamic “caliphate”. The former Christian inhabitants of Mosul and the surrounding towns are now refugees in the semi-autonomous Kurdistan Region nearby, protected from the summer heat and winter snow only by UN-provided tents erected in local churchyards.

“We were given just a few hours to leave Mosul,” one of the refugees told me last summer in the sun-scorched streets of Erbil,

capital of the Kurdistan Region. “We fled to Qaraqosh [a Christian town just east of Mosul] and then Islamic State came there, too, and we had to flee Qaraqosh.”

He was one of a group of men sitting by the road under the shade of a wall; this was how they spent their days, because the tents in which they slept provided barely enough room at night and were left during the day to the women and children. Unable to afford cigarettes, the men passed the time chatting and then at mealtimes headed to the church-organised canteen that handed out free food. Not that there was much help on offer for them, the refugee said. Nobody cared about them and any aid that was supposed to reach them was being siphoned off. “Nothing like this,” he said dolefully, “has ever happened before.”