The word Halloween has its origins in the Catholic Church, coming from a contraction of Hallowed Eve. November 1, or All Saints Day, is a Catholic day of observance in honor of saints, but the history of Halloween goes much farther back than the Catholics or the name.
In 5th century BC Ireland, summer officially ended on October 31. The Celts believed that on this day ghosts walked and mingled with the living. The holiday was called Samhain (sow-en) which marked the third and final harvest of the year, the Celtic New Year.
The reason the Celts celebrated this day as New Year, rather than Yule like other European pagans, was probably due to the fact the that the sun is at its lowest point on the horizon, as measured by the ancient standing stones of Britain and Ireland.
The Druids sacrificed to their deities by burning victims in wicker cages. Prior to the ceremony, all other fires extinguished and were then re-lit from the sacrificial fire.
Today modern pagans and Wiccans celebrate Halloween or Samhain as the New Year, the day when the veil between the living and the dead is at its thinnest. The pagan god dies at Samhain, only to be re-born again at Yule. For these pagans, Samhain is a day for remembering and honoring the dead and celebrating the eternal cycle of reincarnation.
Pope Boniface was instrumental in superimposing a Christian festival over the pagan traditions. Originally, the holidays took place on May 13, but a century later, Pope Gregory III changed it to the present November 1. October 31 was no longer the last day of the year and Samhain was reassigned to the Feast of All Saints.
It is interesting to note that many of the customs surrounding the observance of the Christian All Souls Day also center around accessibility to the dead. In fact, many customs with their origins in pagan traditions have survived to the present. In addition to the souls of the dead alleged to be roaming about, the devil, witches and other assorted monsters and goblins are believed to be at the peak of their supernatural powers.
In Europe, Halloween eventually evolved into a celebration for children. "Ghosts" went from door to door asking for treats, or else a trick would be played on the owners of the home. When millions of Irish immigrated to the United States in the 1840s the tradition followed them.