Actually, I disagree that it was spread by martyrdom the first two centuries. Or at least I disagree that that fact is established. There is very little historical evidence of how it was spread (or even what it was) until the middle of the Second Century. Some aspect of it was certainly connected to the pagan mysteries and Neo-platonic philosophy (the earliest "apologists" and the authentic Pauline epistles are more about Neoplatonist notions of the Divine Logos and Hebrew "Wisdom" as revealed in a secret revelation contained in the Hebrew Scriptures then they are about a historical Jesus). Some aspect of it was certainly connected to apocalyptic sects inspired by Jewish mysticism of the day. Indeed, the historical record DOES confirm that eductated, Greek-speaking Jews of the Diaspora were engaged in synthesizing Jewish mysticism, Greek philosophy and the pagan mysteries in cosmopolitan places like Alexandria. One obvious example: Philo the Pythagorean. The real problem is that the actual historical records were systematically altered and destroyed to create a false impression of unity in the faith in the first two centuries - creating a misleading image of unity both in the theology and history as understood by early believers. There is enough of the historical record recovered to demonstrate a clear absence of unity in how the faith was interpreted. The historical accounts written by Eusebius survived because they were sympathetic to a certain version of that history and appear to have been written for the very purpose of composing a sympathetic history for the Roman Church. Dissent from this historical view was then systematically destroyed. Does that mean that Eusebius account is wrong? No. However, unfortunately, it does leave us with a vague and unreliable historical record of the first two centuries of Christianity that may and probably was influenced by political forces at the time of Rome's adoption of Christianity as the official religion of the Empire.