WAS THE BUDDHA a demon? While few mainline Christians would put the matter in such confrontational terms, any religion claiming exclusive access to truth has real difficulties reconciling other great faiths into its cosmic scheme. Most Christian churches hold that Jesus alone is the Way, the Truth, and the Life, and many also feel an obligation to carry that message to the world's unbelievers. But this creates a fundamental conflict with the followers of famous spiritual figures like Mohammed or Buddha, who preached radically different messages. Drawing on a strict interpretation of the Bible, some Christians see these rival faiths as not merely false, but as deliberate traps set by the forces of evil. Being intolerant of other religions - consigning them to hell, in fact - may be bad enough in its own right, but it increasingly has real-world consequences. As trade and technology shrink the globe, so different religions come into ever-closer contact with one another, and the results can be bloody: witness the apocalyptic assaults in Mumbai. In such a world, teaching different faiths to acknowledge one another's claims, to live peaceably together side by side, stops being a matter of good manners and becomes a prerequisite for human survival. Over the past 30 years, the Roman Catholic Church has faced repeated battles over this question of Christ's uniqueness, and has cracked down on thinkers who have made daring efforts to accommodate other world religions. While the Christian dialogue with Islam has attracted most of the headlines, it is the encounters with Hinduism and especially Buddhism that have stirred the most controversy within the church. Sri Lankan theologians Aloysius Pieris and Tissa Balasuriya have had many run-ins with Vatican critics, and, more recently, the battle has come to American shores. Last year, the Vatican ordered an investigation of Georgetown University's Peter Phan, a Jesuit theologian whose main sin, in official eyes, has been to treat the Buddhism of his Vietnamese homeland as a parallel path to salvation. Following the ideas of Pope Benedict XVI, though, the church refuses to give up its fundamental belief in the unique role of Christ. In a widely publicized open letter to Italian politician Marcello Pera, Pope Benedict declared that "an inter-religious dialogue in the strict sense of the term is not possible." By all means, he said, we should hold conversations with other cultures, but not in a way that acknowledges other religions as equally valid. While the Vatican does not of course see the Buddha as a demon, it does fear the prospect of syncretism, the dilution of Christian truth in an unholy mixture with other faiths. Beyond doubt, this view places Benedict in a strong tradition of Christianity as it has developed in Europe since Roman times. But there is another, ancient tradition, which suggests a very different course. Europe's is not the only version of the Christian faith, nor is it necessarily the oldest heir of the ancient church. For more than 1,000 years, other quite separate branches of the church established thriving communities across Asia, and in their sheer numbers, these churches were comparable to anything Europe could muster at the time. These Christian bodies traced their ancestry back not through Rome, but directly to the original Jesus movement of ancient Palestine. They moved across India, Central Asia, and China, showing no hesitation to share - and learn from - the other great religions of the East.

Just how far these Christians were prepared to go is suggested by a startling symbol that appeared on memorials and stone carvings in both southern India and coastal China during the early Middle Ages. We can easily see that the image depicts a cross, but it takes a moment to realize that the base of the picture - the root from which the cross is growing - is a lotus flower, the symbol of Buddhist enlightenment. In modern times, most mainstream churches would condemn such an amalgam as a betrayal of the Christian faith, an example of multiculturalism run wild. Yet concerns about syncretism did not bother these early Asian Christians, who called themselves Nasraye, Nazarenes, like Jesus's earliest followers. They were comfortable associating themselves with the other great monastic and mystical religion of the time, and moreover, they believed that both lotus and cross carried similar messages about the quest for light and salvation. If these Nazarenes could find meaning in the lotus-cross, then why can't modern Catholics, or other inheritors of the faith Jesus inspired? Many Christians are coming to terms with just how thoroughly so many of their fundamental assumptions will have to be rethought as their faith today becomes a global religion. Even modern church leaders who know how rapidly the church is expanding in the global South tend to see European values and traditions as the indispensable norm, in matters of liturgy and theology as much as music and architecture. Yet the reality is that Christianity has from its earliest days been an intercontinental faith, as firmly established in Asia and Africa as in Europe itself. When we broaden our scope to look at the faith that by 800 or so stretched from Ireland to Korea, we see the many different ways in which Christians interacted with other believers, in encounters that reshaped both sides. At their best, these meetings allowed the traditions not just to exchange ideas but to intertwine in productive and enriching ways, in an awe-inspiring chapter of Christian history that the Western churches have all but forgotten. To understand this story, we need to reconfigure our mental maps. When we think of the growth of Christianity, we think above all of Europe. We visualize a movement growing west from Palestine and Syria and spreading into Greece and Italy, and gradually into northern regions. Europe is still the center of the Catholic Church, of course, but it was also the birthplace of the Protestant denominations that split from it. For most of us, even speaking of the "Eastern Church" refers to another group of Europeans, namely to the Orthodox believers who stem from the eastern parts of the continent. English Catholic thinker Hilaire Belloc once proclaimed that "Europe is the Faith; and the Faith is Europe."

But in the early centuries other Christians expanded east into Asia and south into Africa, and those other churches survived for the first 1,200 years or so of Christian history. Far from being fringe sects, these forgotten churches were firmly rooted in the oldest traditions of the apostolic church. Throughout their history, these Nazarenes used Syriac, which is close to Jesus' own language of Aramaic, and they followed Yeshua, not Jesus. No other church - not Roman Catholics, not Eastern Orthodox - has a stronger claim to a direct inheritance from the earliest Jesus movement. The most stunningly successful of these eastern Christian bodies was the Church of the East, often called the Nestorian church. While the Western churches were expanding their influence within the framework of the Roman Empire, the Syriac-speaking churches colonized the vast Persian kingdom that ruled from Syria to Pakistan and the borders of China. From their bases in Mesopotamia - modern Iraq - Nestorian Christians carried out their vast missionary efforts along the Silk Route that crossed Central Asia. By the eighth century, the Church of the East had an extensive structure across most of central Asia and China, and in southern India. The church had senior clergy - metropolitans - in Samarkand and Bokhara, in Herat in Afghanistan. A bishop had his seat in Chang'an, the imperial capital of China, which was then the world's greatest superpower. When Nestorian Christians were pressing across Central Asia during the sixth and seventh centuries, they met the missionaries and saints of an equally confident and expansionist religion: Mahayana Buddhism. Buddhists too wanted to take their saving message to the world, and launched great missions from India's monasteries and temples. In this diverse world, Buddhist and Christian monasteries were likely to stand side by side, as neighbors and even, sometimes, as collaborators. Some historians believe that Nestorian missionaries influenced the religious practices of the Buddhist religion then developing in Tibet. Monks spoke to monks. In presenting their faith, Christians naturally used the cultural forms that would be familiar to Asians. They told their stories in the forms of sutras, verse patterns already made famous by Buddhist missionaries and teachers. A stunning collection of Jesus Sutras was found in caves at Dunhuang, in northwest China. Some Nestorian writings draw heavily on Buddhist ideas, as they translate prayers and Christian services in ways that would make sense to Asian readers. In some texts, the Christian phrase "angels and archangels and hosts of heaven" is translated into the language of buddhas and devas. One story in particular suggests an almost shocking degree of collaboration between the faiths. In 782, the Indian Buddhist missionary Prajna arrived in Chang'an, bearing rich treasures of sutras and other scriptures. Unfortunately, these were written in Indian languages. He consulted the local Nestorian bishop, Adam, who had already translated parts of the Bible into Chinese. Together, Buddhist and Christian scholars worked amiably together for some years to translate seven copious volumes of Buddhist wisdom. Probably, Adam did this as much from intellectual curiosity as from ecumenical good will, and we can only guess about the conversations that would have ensued: Do you really care more about relieving suffering than atoning for sin? And your monks meditate like ours do?