Halloween starts the triduum of Allhallowtide, the time dedicated in remembering the dead including the martyrs, saints (hallow), and departed believers. The traditional focus involves the use of humor and ridicule to deal with the power of death. All Hallows' Eve is influenced by Celtic harvest festivals as a Christian feast. Commercialization started in the 1900s with costumes appearing in the 1930s and 'trick-or-treating' in the 1950s.