The list is in two parts: Free-use materials that can be freely used with no concerns about copyright (because they are in the public domain), and hymns that may still be copyright depending on the laws in your country.
About Martyrs
The common understanding of a martyr is someone who is killed or suffers greatly because of something or someone they are committed to. In a religious sense, this commitment is to their faith or church-membership.
Some Christian churches take the step of declaring certain people to be Martyrs. The Roman Catholic church does this, and in very broad terms, looks at whether a person has:
- Given witness to their faith
- Died due to persecution by someone / something motivated by a hostility toward Jesus Christ, the Church or Christian virtues, and
- Voluntarily accepted that death is the only option if they will not commit apostasy or break God's law.
That said, many books and articles have been written about what these criteria mean and how they fit certain situations. For example the "Holy Innocents", viz male children under age 2 who were killed by King Herod in an attempt to kill Jesus, are regarded as martyrs even though the witness they gave at such a young age was probably limited. And as with Saints vs saints, there are likely to be many people who would meet the criteria, but their lives are not examined, or evidence cannot be found.
Image adapted from a hand-colored devotional print of early martyr Saint Sebastian tied to a tree and pierced with arrows, produced by Augsburg publisher Johann Georg Gleich in the18th or early 19th century