Who of the 12 apostles was martyred?
To the best of my knowledge the Bible only has record of one. James’ murder is mentioned in the book of Acts ch. 12 verse 2. Jesus’ prophecy of Peter’s death is told in the book of John ch.21 verse 18-19. The Apostle John was exiled to the Greek island Patmos and is believed to have died in the Turkish regions of old age. Church traditions however show that 11 of the 12 were martyred. Hope this helps.