"Early martyrs" refers to people who were persecuted or killed for their beliefs, usually relating to their religious or political views, during the early history of a particular religion or movement. Full definition
When we learn about early martyrs, we can see their honesty, sincerity, zeal and courage to face persecution. (religion-online.org)
I think that is the view you have because of the weight you give the early martyrs in validating your beliefs, e.g. «people would not die for what they don't believe». (religion.blogs.cnn.com)
I see your point Dan, but to make martyrs be a proof of historicity you might want to specify the earliest martyrs, that is those who actually saw Jesus and perhaps those who heard about it from them. (redeeminggod.com)