In late December, the plains of North India turn suddenly cold and grey. Towards evening, as the sun is beginning to set over the minarets of the village mosques, smoke from the buffalo-dung cooking-fires begins to mass in a flat layer at the level of the tree tops. By dusk, the layer has turned into a vaporous mist which thickens and curdles overnight to form by morning a dense fog.

Some fifteen years ago, on just such a bleak, cold dawn, I climbed the long flight of ceremonial steps leading up to the great mosque at Fatehpur Sikri. This lay in the heart of the ruined Moghul capital built by the sixteenth century Emperor Akbar, a few miles to the West of Agra. I was a nineteen year old backpacker, and it was my first visit to India. I had just spent my first Christmas away from home, and I was enjoying the sensation of complete disorientation. It was immediately after Christmas, I kept thinking, but not only was there not a Christmas tree or a Christmas decoration in sight, there was nothing even remotely Christian to be seen- or so I thought.

For when I reached the top of the steps that rose to the Buland Darwaza- the massive domed, arched gate leading into the Imperial mosque- I saw something that confused me even further. Here was one of the greatest pieces of Muslim architecture in India, but according to my guide book, the strip of Persian calligraphy which framed the arch read as follows: “Jesus, Son of Mary (on whom be peace) said: The World is a Bridge, pass over it, but build no houses upon it. He who hopes for a day, may hope for eternity; but the World endures but an hour. Spend it in prayer, for the rest is unseen.”

The inscription was doubly surprising: not only was I taken aback to find an apparently Christian quotation given centre stage in a Muslim monument, but the inscription itself was unfamiliar. It certainly sounded the sort of thing Jesus might have said, but did Jesus really say that the world was like a bridge? And even if he had, why would a Muslim Emperor want to place such a phrase over the entrance to the main mosque in his capital city? Weren’t Christians regarded as the enemies and rivals of the Muslims- and vice versa? This was certainly the impression I had been given at my Catholic school where I had only ever come across Islam in the confrontational context of the Crusades.

It was only much later, after I had lived and travelled in India and the Middle East for several years that I began to be able to answer some of these questions. The phrase emblazoned over the gateway was, I learned, one of several hundred sayings and stories of Jesus that fill Arabic and Islamic literature. Some of these derive from the four canonical gospels, others from now rejected early Christian texts like the Gnostic Gospel of Thomas, others again from the wider oral Christian culture-compost of the Near East- possibly authentic sayings and stories, in other words, which Islam has retained but which Western Christianity has lost.

These sayings of Jesus circulated around the Muslim world from Spain to China, and many are still familiar to educated Muslims today. They fill out and augment the profoundly reverential picture of Christ painted in the Koran where Jesus is called the Messiah, the Messenger, the Prophet, Word and Spirit of God, though- in common with some currents of heterodox Christian thought of the period- his outright divinity is questioned. The Koran calls Christians the ‘nearest in love’ to Muslims, whom it instructs in to “dispute not with the People of the Book [that is, the Jews and Christians] save in the most courteous manner… and say ‘we believe in what has been sent down to us and what has been sent down to you; our God and your God is one’.”

I have been thinking a lot about that quotation over the last three months. Ever since September the 11th we have seen some of the right-wing ‘Qualities’- as well as the tabloids- united in an often virulent bout of Islamophobia, as a hundred instant experts in Islam have popped up to offer their disparaging views on a religion few seem ever to have encountered in person. After the scale of horror of the atrocity in New York perhaps this sort of thing is inevitable; but it doesn’t alter the fact that the image these writers are projecting of Islam- particularly vis-a-vis its relations with Christianity- is a ludicrously unbalanced, inaccurate and one-sided one.

For the links that bind Christianity and Islam are so deep, and so complex, and so intricately woven, that the more you learn about them, the more the occasional confrontations between the two religions begin to seem like a civil war between two different streams of the same tradition than any essential clash of two incompatible civilisations.

When the early Byzantines were first confronted by the Prophet's armies in the seventh century, they assumed that Islam was merely a variant form of Christianity: Islam of course accepts much of the Old and New Testaments, obeys the Mosaic laws about circumcision and ablutions, and venerates both Jesus and the ancient Jewish prophets. The early Life of Muhammad relates how, when Muhammad entered Mecca in triumph and ordered the destruction of all idols and images, he came upon a picture of the Virgin and Child inside the Ka’ba. Reverently covering the icon with his cloak, he ordered all other images to be destroyed, but the image of the Madonna to be looked on as sacrosanct.

When Muhammad's successor Abu Bakr stood on the borders of Syria he gave very specific instructions to his soldiers: “In the desert,” he said, “you will find people who have secluded themselves in cells; let them alone, for they have secluded themselves for the sake of God.” Likewise, when his successor Omar went to Syria, he actually stayed with the Bishop of Ayla and went out of his way to meet the Christian Holy Men in the town. For many years Muslims and Christians used to pray side by side in the great churches of the Middle Eastern cities: in Damascus, for example, the great basilica of St John was used for worship by both Christians and Muslims; only fifty years later were Christians obliged to pray elsewhere and the building formally converted into what is now known as the great Ummayad mosque.

As late as 649 AD a Nestorian bishop wrote: “These Arabs fight not against our Christian religion; nay, rather they defend our faith, they revere our priests and saints, and they make gifts to our churches and monasteries.” There were never any conversions by the Sword, a myth much propagated in anti-Islamic literature.

Indeed, the greatest theologian of the early church, St. John of Damascus (d. 749), was convinced that Islam was at root not a new religion, but instead a variation on a Judeo-Christian form. This perception is particularly remarkable as St. John had unique access to the fountainhead of Islamic thinking in the earliest days of the faith. He had grown up in the Ummayad Arab court of Damascus- the hub of the young Islamic world- where his father was chancellor, and he was an intimate boyhood friend of the future Caliph al-Yazid; the two boys drinking bouts in the streets of Damascus were the subject of much horrified gossip in the streets of the new Islamic capital. But, in his old age, St. John took the habit at the remote desert monastery of Mar Saba, where he began work on his great masterpiece, the Fount of Knowledge.

I first really heard about St John of Damascus and his writings was when I went to spend a few night in Mar Saba in the course of a journey around the monasteries of the Middle East in 1994. Mar Saba lay tucked into a cliff face in the wastes of Judea, a spectacular near vertical plunge of chapels, cells and oratories. One night, while the monks were still singing their vespers in the chapel, and their chant of their kyries were echoing around the rock-cut corridors of the monastery, I was taken by the monastery guestmaster to see the cave with St John wrote The Font of Knowledge. With a flickering storm lantern in his hand, he led the way to a small cell backing onto a rock wall, its ceiling cut so low as to make standing virtually impossible.

“St John spent thirty years in that cell,“ he said. “Although he could not stand he hardly ever went out of it. He believed he had become too proud of his high position in the court of Damascus, so he chose this cave in which to live as a monk.”

It was here that St John of Damascus wrote his critique of Islam, the first ever penned by a Christian. Intriguingly, John- the ultimate insider- regarded Islam as a form of Christianity closely related to the heterodox Christian doctrine of Arianism: after all this doctrine, like Islam, took as its starting point the idea that on Christmas Day God could not have become fully human without somehow compromising his divinity.

Used to the often surrealistic scriptures of the Gnostics, then in widespread circulation among the Christians of the Near East, John was apparently unworried by the points where the Koran diverges from the basic narrative of the Gospels- such as the very full but oddly unfamiliar description it gives of the first Christmas. In this Koranic version, Jesus' birth takes place not in a stable but under a palm tree in an oasis, shortly after which the Christ child, still in his swaddling clothes, sits up and addresses Mary’s family with the words: “I am the servant of God. He has given me the Gospel and ordained me a prophet . His blessing is upon me wherever I go, and he has commanded me to be steadfast in prayer and to give alms to the poor as long as I shall live. I was blessed on the day I was born; and blessed I shall be on the day of my death; and may peace be upon me on the day when I shall be raised to life. “

Islam of course grew up the largely Christian environment of the Late Antique Levant, and the longer you spend in the ancient Christian communities of India the Middle East, the more you become aware of the extent to which Eastern Christian practice formed the template for what were to become the basic conventions of Islam. The Muslim form of prayer with its bowings and prostrations appears to derive from the older Syrian Orthodox tradition that is still practised in pewless churches across the Levant. The architecture of the earliest minarets, which are square rather than round, unmistakably derive from the church towers of Byzantine Syria, while Ramadan, at first sight one of the most distinctive of Islamic practices, bears startling similarities to Lent, which in the Eastern Christian churches still involves- as it once used to in the West- a gruelling all-day fast.

Perhaps no more branch of Islam shows so Christian influence as Islamic mysticism or Sufism. . For Sufism with its Holy Men and visions, healings and miracles, its affinity with the desert and its emphasis on the mortification of the flesh and the individual's personal search for union with God, has always borne remarkable similarities to the more mystical strands of Eastern Christianity, and many Muslim saints- such as the great Mevlana Rumi- worked to reconcile the two religions. Indeed the very word Sufi seems to indicate a link with Christianity. For Suf means wool which was the characteristic clothing material of Eastern Christian monks which was taken over by the early Mystics of Islam. Other styles of dress adopted by the Sufis are also anticipated in pre-Islamic Christianity: the patchwork frock made from rags, and the use of the colour of mourning, black for the Christians, dark blue for the Muslims. Another interesting link- at the extreme edge of both Christian and Muslim asceticism- is the wearing of heavy chains. This was a practice first adopted by the Christian Grazers and which was later adopted by some Sufi sects. Through punishing the flesh, such exercises were believed by both groups pf ascetics to induce visions and spiritual ecstasy.

Certainly if a monk from sixth century Byzantium were to come back today it is probable that he would find much more that was familiar in the practices and beliefs of a modern Muslim Sufi than he would with, say, a contemporary American Evangelical. Yet this simple truth has been lost by our tendency to think of Christianity as a thoroughly Western religion rather than the Oriental faith it actually is. The recent demonisation of Islam in the Christendom, and deep and growing resentment felt in the Islamic world against the Christian West, has created an atmosphere where few on either side are still aware of, or even wish to be aware of, the profound kinship of Christianity and Islam.

I first came across the idea of Christ as an object of Muslim devotion when I read that inscription quoting Jesus, son of Mary, on Whom be Peace, on the gateway at Fatehpur Sikri. Last month I came across a Mughal miniature, now on display in the British Library, which was probably painted within that city soon after the gateway had been built. It is a nativity scene, with Mary and the Christ child and wise men coming to offer gifts. But the wise men are Mughal courtiers, Mary is attended by a Mughal serving girls, and the Christ child and his mother are sitting under a palm tree. As this miniature shows, there are certainly major differences between the two faiths- not least the central fact, in mainstream Christianity, of Jesus' divinity. But Christmas – the ultimate celebration of Christ’s humanity- is a feast which Muslims and Christians can share together without reservation. At this moment when the Christian West and Islamic East seem to be heading for another major confrontation, there has never been a greater need for both sides to realise what they have in common and, as in this miniature, to gather around the Christ child, to pray for peace.

Mr. Ron Jacobs is the author of The Way the Wind Blew: A History of the Weather Underground (Verso, 1997).