Outside the church of Our Lady of Salvation in Baghdad, I watched an old woman dressed in black move slowly up to a huge poster hanging at the gate, displaying photographs of the 50 or so people murdered during a Sunday mass in October.

She stopped and kissed two of the images. A son, a brother, a cousin? I don’t know. But I had already met Zuhair and Amal whose 33-year old son Uday and 4-year old grandson Adan were shot and killed when Islamist terrorists beseiged, shot and threw grenades into the church. Their 16-year old daughter, Mirna, dressed in mourning black, described how she played dead to avoid being killed as well.

Their house is full of photographs, and they wanted to show us the most painful reminders: Uday and his wife’s empty room, Adan’s toys, the baby cot for their 11-month old granddaughter who was shot in the leg and is now in Italy with her mother, undergoing hospital treatment.

The women wept as they told their story and I found it hard not to weep too.

The church with its bullet holes and blood stains took me back to Rwanda, where hundreds of thousands were massacred in churches. About 40 turned up for mass – Zuhair and Amal, not surprisingly, can’t bear to re-enter the place. The little congregation, diminished by death and fear, sang and prayed. Incense and chanting filled the air.

The church of Our Lady of Salvation has become a potent symbol because Christianity is in decline across the Middle East, and most rapidly in Iraq. Numbers are hard to come by, but hundreds of thousands have left Lebanon, Syria, Palestine and Egypt in the last twenty years.

In Iraq, people say there were maybe a million Christians in 2003 – 3 per cent of the population – but at least half have left and those remaining now want to go too, as extremist Islamists step up their campaign against “infidels”. Many of those I’ve met in the last week say there’s no future for Christians in Iraq – it’s over.

Yet Christianity was in Mesopotamia – what we now call Iraq – several centuries before Islam. The Chaldeans and Syriac Christians of today speak Aramaic, the language Jesus would have spoken. The reason so much attention is being lavished on the murder of Christians is not because their lives are worth more than the lives of Muslims, but because an ancient civilisation is in danger of being wiped out.

On Sunday afternoon, I went to St George’s Anglican church where an English vicar is trying to stem the tide. The indefatigable Canon Andrew White, who doesn’t let the progression of multiple sclerosis hinder him, attracted several hundred to his Christmas carol service. It was wonderfully, eccentrically English and Iraqi.

The children, all shapes and sizes, a few wearing knitted hats in seasonable scarlet, stood in front of the altar singing “We Wish You a Merry Christmas” in English and Arabic with minimal attention to melody. The sound system screeched, and Father Christmas was trundled down the aisle in a box on wheels covered in red cloth and gold tinsel. He cast sweets into the pews.

A Sunni sheikh, drafted in to reassure the congregation that the majority of Muslims stood with them, looked on, slightly baffled. They recited the Lords Prayer in Aramaic. Outside, members of the Mothers’ Union Baghdad Branch (twinned with Portsmouth) sorted the frozen chickens and other groceries to be given to each family.

I asked Canon White what he said when Christians asked him whether they should stay or leave.

“It’s very hard,” he said. “I can’t tell people what to do. But it’s important that we maintain a Christian presence here, because Christianity is the root of Iraq. If you cut the root, it’s finished.”