Why would people suffer and be martyred for a fiction?
It is widely accepted that most of the Apostles and other eye witnesses of the life, death and resurrection of Jesus were persecuted and martyred for speaking out about it, by the Jews, the commercial interests whose trade depended on the Pagan religion and also by the Romans.
They could have avoided this by simply keeping quiet. But they didn’t. If they hadn’t been convinced of the truth of what they were proclaiming, whether by direct experience or by hearing from their fellows, it would make no sense for them to maintain their story knowing that they would be martyred for it. There was nothing for them, or anyone else, to gain by doing so.
During the so-called trial of Jesus, the Apostle Peter was so scared that he denied ever knowing Jesus at all. After Jesus was crucified, the Apostles were clearly scared of the Jewish authorities in case they would be next and hid behind locked doors.
Their Rabbi and the man they considered as their saviour had been executed in a particularly painful and degrading manner. They would have everything to gain from distancing themselves from Jesus and, on the face of it, nothing to lose.
This video gives a list of the prominent martyrs in the first few centuries after Jesus, including those who were eye witnesses to the reality of the risen Christ. There were many, many others.
Although most of the persecution which the early Christians received was not from the Roman Empire, there were an increasing number of such occasions. For instance:
In 170AD, Emperor Trajan had many of them killed by wild beasts in the Arena.
In 303-304 AD, Emperor Diocletian published 4 edicts which outlawed Christianity and led to extreme violence against them.
This policy of suppression by persecution back fired when many faced martyrdom willingly and confounded the crowd who expected a spectacle. Even the lions who were sent in to kill them were not used to such a reaction and were reluctant to attack - although they eventually did so.
When the spectators saw this, some would ask “what do they believe that would produce such calm in the face of death?”
Rather than discouraging the spread of Christianity, persecution furthered it.
How reliable is the evidence of the martyrs for the truth of Christianity? They certainly believed what they died for. Could they have been mistaken? The authorities could have discredited the claims of resurrection simply by producing the body of Jesus. They wanted to prove the resurrection false so they would have done so it they could. But they did not.
50 days after the death of Jesus, the number of believers had risen to about 120.
Then came the Jewish feast of Pentecost and the believers were filled with the Holy Spirit and began to boldly speak out what they had seen and heard with a blatant disregard for the consequences or for their own safety.
What happened on that day? More than can be explained by anything other than God Himself filling and transforming them, empowering them to speak boldly and to endure suffering. Nothing else would have convinced them to take that route.
The willingness of the first Christians to be martyred is both the evidence for the truth of the message they were being martyred for and also, despite the persecutors, was the means by which the message spread.