In the book How the Irish
Saved Civilization (Doubleday), Thomas Cahill talks about both green and white
martyrdom. According to Cahill, Ireland was unique in that Christianity was introduced
there without bloodshed (red martyrdom).
Cahill states that this lack of martyrdom disturbed the Irish, so they
conceived first of a green martyrdom. Green martyrs left behind the comforts and pleasures of ordinary human society to live
hermits' lives on mountaintops or lonely islands.
Against this background Cahill introduces Columcille ("Dove of God")—also
called Columba or Crimthaann. Born in 521, a prince with a title to kingship, he chose
to become a monk. Columba, with 12 relatives, founded a monastery on Iona off the coast of Scotland that
became famous throughout Europe.
Monks from Iona in turn set out for what they called
a white martyrdom: "[H]enceforth all who followed Columcille's lead were called
to the white martyrdom, they who sailed into the white sky of morning, into the unknown,
never to return."