The holiday of Halloween derives from Hallowmas, is based on Samhain and has symbols tied to Wiccans from the Middle Ages. For example, bats, black cats and spiders are all important components of Halloween, and all were associated with witchcraft.
Halloween is based on both Hallowmas and Samhain, the former of which was a Catholic holiday honoring saints that fell on Oct. 31 to Nov. 2. The Catholic Church established Hallowmas on those specific days to usurp the pagan holiday of Samhain or All Hallows' Eve.
Samhain, a Celtic festival, celebrates the end of summer and the beginning of winter. It had very little to do with death. However, it did play a role in adding the tradition of wearing of costumes because the Celts believed that the spirit world was especially close to the real world during this time, and costumes helped to confuse the spirits.
Trick-or-treating has been around for centuries, but originally was a way for poor people to beg for food, a practice called "guising" or "souling." The Irish introduced trick-or-treating to the United States in the early 1900s. Wiccans still celebrate its original Samhain roots of Halloween and consider it the beginning of the New Year.