From the fourth to the sixteenth century c.e. in Europe, philosophy and science were in the service of Christianity. The arrival of modern physical science, and with it the transition from faith alone as a source of authority to faith together with secular reason as dual sources of authority, was the most momentous intellectual change in the history of Western civilization. In Europe, prior to the scientific challenges to religious belief, the only intellectual competition that Christianity had faced had come from other religions. Christian religious belief has not only survived, it has flourished. Christians could always respond, as Rudolf Bultmann had, by withdrawing their belief in the literal truth of their core beliefs and espousing a "demythologized" version of their faith. That is, they could respond by giving up their conviction that the account of Jesus in the New Testament is reliable and simply admitting that it is myth.