No event during the first millennium was more unexpected, more calamitous, and more consequential for Christianity than the rise of Islam. Few irruptions in history have transformed societies so completely and irrevocably as did the conquest and expansion of the Arabs in the seventh century. And none came with greater swiftness. Within a decade three major cities in the Byzantine Christian Empire--Damascus in 635, Jerusalem in 638, and Alexandria in 641-fell to the invaders.
When reports began to circulate that something unusual was happening in the Arabian Peninsula, the Byzantines were preoccupied with the Sassanians in Persia who had sacked Jerusalem in 614 and made off with the relic of the True Cross. And in the West they were menaced by the Avars, a Mongolian people who had moved into the Balkans and were threatening Constantinople. Rumors about the emergence of a powerful leader among the Arabs in the distant Hijaz seemed no cause for alarm.
Even on the eve of the conquest of Jerusalem, when Arab armies had encircled the holy city and blocked the road to Bethlehem, the patriarch of Jerusalem, Sophronius, assured the faithful: "We will laugh at the demise of our enemies the Saracens [as Christians first called the Muslims] and in a short time see their destruction and complete ruin." Fourteen hundred years later the Muslims are still in Jerusalem, and with each passing decade Islam figures larger in the minds of Christians, penetrates more deeply into Christian societies, and, by its fixed and impermeable tenancy of a large part of the globe, circumscribes the practice of Christianity.
From the day Caliph Umar was met by the patriarch Sophronius in Jerusalem in the mid-seventh century, Christianity has found itself face to face with Islam. Though the circumstances have varied from place to place and century to century, Islam has always presented a challenge. Yet, in the course of a long history, during which Islam expanded all over the world, Christians, with the exception of those who lived in the Middle East in the early centuries of Muslim rule, have seldom taken Islam with the seriousness it deserves or recognized it for what it is--a religion in the biblical tradition in which piety is wedded to statecraft. A "complacent ignorance" (in the phrase of the modern scholar Lamin Sanneh) has prevailed, especially in the West.
Before the Muslim conquest, Christians could look back confidently on six hundred years of steady growth and expansion. By the year 300, churches were found in all the cities of the Roman Empire, from Spain and North Africa in the west to Egypt and Syria in the east, as well as in Asia Minor and the Balkans. In the fourth century the Armenians embraced the new religion, and on the eastern shore of the Black Sea the preaching of St. Nino led to the conversion of the Iberian royal house and the adoption of the Christian faith by the Georgians. To the south, Christianity reached Ethiopia in the fourth century and Nubia a century later. And there were Christian communities in Roman Gaul already in the second century and in Britain by the third century.
No less impressive was the spread of Christianity eastward. Accustomed to the colorful maps of Paul's missionary journeys printed in study Bibles, we are inclined to think that the initial expansion took place in the Mediterranean world. But in the vast region east of Jerusalem--Syria, Jordan, and Iraq, where Aramaic was the lingua franca--the majority of people had become Christian by the seventh century. The Christian gospel was carried even farther east to ancient Persia, and from there it traveled along the Silk Road into Central Asia: Uzbekistan, Tajikistan, Afghanistan. At some point during the first six centuries it reached the western shore of India and even China. In the seventh century, the global center of Christianity lay not in Europe but to the east of Jerusalem.
Though the peoples of this vast area spoke many languages and had different customs, through Christianity they were linked together in the confession of the creed of Nicaea. They baptized their infants in the name of the Father and of the Son and of the Holy Spirit, offered the sacrifice of the Eucharist in their churches, were governed by bishops, revered the lives of ascetic men and women living in monastic communities, and had in common a holy book.
Archaeologists have uncovered fragments of ancient Christian texts that make the point powerfully. At both Antrim in Northern Ireland and in Panjikent, near Samarkand, in present-day Uzbekistan, copybooks were found from about the year 700 (wax on wood in Ireland and potsherds in Asia), each containing verses from the Psalms. In Ireland, the schoolboy whose language was Irish had written the psalm verses in Latin, and in Panjikent, the boy whose language was Soghdian had written his lesson in Syriac.
When one considers the extent of Christianity in the year 600, the deep roots Christians had set down all over the world as they knew it, and the interconnectedness of the churches, it is no wonder that Christians had difficulty grasping that the Arab armies occupying their cities were not simply conquerors seeking booty but heralds of a spiritually potent religion and architects of a new civilization.
The first recorded comment of a Christian reaction to Muhammad dates from only a couple of years after his death. When tales of a prophet among the Arabs reached Christian Syria, someone asked an old man, "What can you tell me about the prophet who has appeared with the Saracens?" The old man groaned deeply and said, "He is false, for the prophets do not come armed with a sword." He had in mind of course the Hebrew prophets, Elijah or Isaiah or Amos. A prophet is one called to speak for God.
But his memory of the Bible was imperfect, for he had overlooked the greatest of the prophets before Jesus: Moses. Like the later prophets, Moses was certainly called to speak for God, but, unlike Isaiah or Ezekiel, Moses was also a political and military leader and, let it not be forgotten, a lawgiver. And he carried a sword: In the Book of Numbers, we learn that he armed a thousand men from each tribe of Israel to take vengeance on the Midianites.
It is this biblical prophet, Moses, who was the model for Muhammad. Though Muslims see Abraham as the first to believe in the one God--and thus the first muslim and the ancestor of the Arabs through Ishmael--the prophet mentioned most often in the Qur'an is Moses. Muhammad was, like Moses in the words of St. Stephen in the Acts of the Apostles, "powerful in words and deeds."
And the early spread of Islam was an affair of deeds: vigorous, venturesome, irresistible deeds. In the span of less than a hundred years, Arab commanders made their way from the edge of Egypt along the North African littoral until they reached the Atlantic Ocean. From the Arabian Peninsula they also advanced northeast through Persia and across the Asian steppes to India. The Arabs reached Sind, today a province in Pakistan, in 711. And within the same decade, after crossing the Straight of Gibraltar into Christian Spain, they crossed the Pyrenees and penetrated southern France, to be halted finally at the battle of Poitiers in 732.
By the beginning of the eighth century, Muslims had created in these disparate and distant regions a new community formed by common beliefs and practices and held together in a loose unity by the caliphate established in the ancient Christian city of Damascus. As new territories were conquered, garrison towns arose. The Arabs brought their wives and children, built mosques, and over time founded such new cities as Basra and Kufah in Iraq, Fustat (old Cairo) in Egypt, and Kairouan in Tunisia. By keeping themselves apart initially from the local societies, they were able to maintain their identity in a sea of strange people and gradually displace the culture that had dominated the region for a thousand years.
Soon Islam began to take hold among the conquered peoples--and one reason was that they were already familiar with the biblical tradition on which the Qur'an drew. For example, an entire surah is devoted to the biblical Joseph, the son of the patriarch Jacob, viceroy of Egypt.
At first Arabic was spoken only by the Arabs, but by the end of the seventh century, during the...