Although it has become a retailers' marketing frenzy in recent years, the elemental traditions of Halloween remain intact, and are rooted in ancient traditions dating back to pre-Christian times.
Halloween is derived from the ancient Celtic festival of Samhein (pronounced sow-in), which was initiated by the Druids (Celtic priests) in the British Isles, who honored a god of the dead on this day. The Druids can be traced as far back as 2 B.C., which gives Halloween an ancient heritage, to be sure! Samhein was the Celtic New Year's Eve, with November 1 being the first day of winter and of the new year. This most important festival of the Celtic year was a joyful holiday, yet tinged with foreboding. For the Celts believed that the veil between the earthly and the spirit worlds was at its thinnest on this night, and that the souls of departed ancestors were free to roam the earth, along with fairies, witches, and demons.
Many of the Samhein customs focused on either welcoming the loving souls of the dearly departed or warding off the evil spirits of the demons. When the Celts feasted on this day, they made sure to set a place at the table for their deceased loved ones. At the conclusion of the feast, a meal was set outside for the spirits that wander in the night. They might also leave milk on the windowsill with a white candle to appease wandering souls and fairy folk.
Illumination was a major theme for the ancient Samhein festivals, and bonfires dotted hillsides all over the British Isles on this night. Jack-o-lanterns were also used to light the way for the ancestor spirits, and to frighten away any unfriendly spirits. They were traditionally carved out of turnips; it wasn't until the 19th century that U.S. immigrants turned the pumpkin into a Halloween custom. Even today, a flickering jack-o-lantern with a lopsided leer is the ubiquitous symbol of Halloween!
Dressing in costume on this night originated, at least partially, in Scotland, where the custom of "guising" was used to scare away malicious spirits. As the centuries passed, people began dressing like these dreadful creatures and performing antics in exchange for food and drink. This practice, called "mumming," came to the U.S. with Irish immigrants in the 19th century, and is what we now know as trick-or-treating.