The question contained in this chapter’s title continues to elicit many answers from academics, particularly in publications addressed to a larger audience.1 As has been observed by more than one scholar, however, the answers have not changed much since the time of Edward Gibbon (1737–94).2 Moreover, in my view the answers typically given are not fully convincing, so I take the opportunity here to reconsider the question – in fact, even to question the question. Instead of a critical review of the answers typically offered, I seek to deconstruct the question, using the words that compose the title of the chapter as a guide for uncovering the many assumptions that lay behind it. As a result, I will complicate the picture and illustrate the many ways that things can go wrong if fundamental assumptions embedded within the question are left unexposed, as is usually the case.

This chapter reviews the networks that made possible the diffusion of the beliefs and practices associated with the figure of Christ during the first and second centuries and concludes that the missionary, the pious merchant, and the occasional Christian traveler should definitively be discarded as likely agents of religious change. Complex contagions such as the diffusion of religious beliefs and practices require as agents individuals who have strong ties, and therefore social capital, in the different networks among which they circulate. In turn, the local networks of diffusion must be both strong-tie and sufficiently open. These findings invite a reopening of the question of the role of the Jewish Diaspora in the spread of Christianity beyond the first century.