Christianity is under siege in the very place where it was born. Hundreds of thousands of Christians have fled Iraq and Syria in the face of Islamic extremism and conflict. After a six-week trip across the Middle East in which I met church leaders and embattled congregations, it is clear to me that Christianity is hanging by a thread, and may not survive in some places. Some Christians said that after the brutality they had suffered and witnessed, they feared that relations with their Muslim neighbours could never be restored. In Iraq the situation is critical. I visited the monastery of St Matthew, which has occupied a mountain top above the plain of Nineveh, in the north of the country, since the fourth century. Below you can hear artillery blasts and see western airstrikes on Islamic State positions. When Christianity stretched across the Roman empire, 7,000 monks worshipped here: today only six are left, and hardly anyone dares visit the ancient site which could soon become just a relic of Christianity in the region. Many of the inhabitants of the Christian villages in the valley below the monastery have fled to Irbil, in Kurdistan, where more than a thousand displaced Christian families are camped in a half-built shopping mall. Leila and Imad Aziz fled Mosul last summer when Islamic State occupied the city, and gave Christians the same harsh choices faced by their ancestors under Muslim rulers centuries ago: convert to Islam, leave the city, or pay the jizya -- a heavy Christian tax. "We can't go back to Mosul for fear of being killed, kidnapped or robbed," Imad told me. Like many Christians the couple once had a good life and a successful business. Leila crosses herself as she remembers passing through Isis roadblocks where their money, jewellery, even clothes were taken. "We can't ever return to Mosul as we have nothing left there" says Leila. Imad believes Christians have become an endangered species in the region. "I believe that in four to five years very few Christians will remain -- they will be able to point a finger at them saying 'he's a Christian'." But what should be remembered is that this wave of Christian persecution began not with Islamic State, but a decade ago in the chaos sparked by the US- and British-led invasion of Iraq. Under Saddam Hussein's rule Christians in fact enjoyed what they now recall as a golden age. They were free to worship and played a full role in society. However, the removal of the dictator let loose an ugly Shia-Sunni power struggle. Father Douglas Bazi, a Catholic priest I met in Irbil, explained the consequences: "They looked at the west as infidels, and as Christians we were seen in the same way". Father Bazi is now caring for 135 families in tents. The priest's church in Baghdad was bombed and he was taken hostage until the church paid a ransom. His captors broke his back with a hammer -- then his teeth, one by one. "If you look at history, we are the same group who lose every time. They push us to lose our faith, our people, our role, our positions, our job, now we have lost our homes -- so what next?" A million people, two-thirds of Iraq's Christians, fled in the decade following the fall of Saddam. The same story is repeated across the Middle East, where the Arab spring unleashed forces that turned against authoritarian leaders and the Christians they once protected. In Syria I visited Maaloula, where 3,000 Christians fled during battles between government forces and Islamic militants. This ancient place of pilgrimage is one of only three places in the world where they still speak Aramaic, the language of Jesus Christ. Christians are starting to come back now that government forces have re-taken the town. One woman showed me the blackened ruined walls of her home and the cafe, she ran for tourists. "We never believed the Muslims would do this to us, but we have to be strong and thank God we are alive," she said. The sixth century monastery of St Sergius was occupied by militants who destroyed precious Christian treasures. Muslim families from Maaloula fled the fighting too but have not been allowed to return -- Christians accuse them of helping the militants. More than 200,000 people have died in Syria's four years of civil war. They are overwhelmingly Muslims, many killed by the Assad regime. But Christians have had to make hard choices. Maaloula was seen as a turning point, and many have now put their faith in the Assad regime as the only option for their religion to survive. As Antoinette Nasrullah told me: "I cannot leave Maaloula -- if there are no Christians here there will be no Christians in Syria." In Damascus I met Father Nawras Sammour, who runs the Jesuit Relief Service, which is feeding 5,000 people a day, mostly Muslims displaced by the war. "This was our way of serving our country in this crisis" says Father Narwas. "Syria is a beautiful mosaic of different communities and it should stay that way". Like many church leaders he cannot accept the Islamist vision of society. The present government is seen as somehow a guarantee of some security for Christians -- but tens of thousands have already fled Syria, never to return. Christianity remains a force only in Lebanon, where the common enemy for Muslims and Christians alike is Islamic extremism. There are other threats, however -- in historic Palestine young Christians leave for jobs and a more secure life abroad. Emigration and fear are sapping the life of Christian communities even in relatively peaceful parts of the region. But it's in Iraq that the religion faces its greatest test. It may even be too late for Christianity to survive on the plain of Nineveh. So should the west, instead of wringing its hands, help them to leave? As Father Bazi told me: "Open the gates, give my people visas." Providing Christians with dignity and the right to life is now paramount. Not, as he says, preparing them once again to be sheep for slaughter.