In about 1625 some Chinese digging the foundations of a house near Xian, China's ancient capital, chanced upon a black marble monument. The Chinese characters inscribed at the top said, "The Monument Commemorating the Propagation of the Ta-ch'in Luminous Religion in the Middle Kingdom." Syriac characters on the stone described the arrival of a missionary, Olopen (or Alopen), in 635. The text also named Chinese emperors who had supported this religion and listed the religion's leaders, including one bishop, 28 presbyters, and 38 others, likely monks.

Olopen may or may not qualify as China's first missionary. For one thing, silk worm eggs were transported from China to Constantinople as early as 551, indicating that traffic—probably monastic traffic—predated Olopen's arrival by several decades. The bigger question, though, hinges on theology: Olopen's "luminous religion" was rooted in Nestorianism.

Let's back up a bit. In 428 a Syrian monk named Nestorius objected to the title "Theotokos," or god-bearer, in reference to Mary. His stance, which was interpreted (possibly misinterpreted) as a rejection of the unified divine and human nature of Christ, was declared heretical by the Council of Ephesus in 431. Nestorianism survived, however, as a group of disaffected eastern bishops organized a Nestorian church in Persia. This location gave the missions-minded ...