Мы эту тему в универе проходили Интересноооо было.Вот пока я нашла кое-что:
The History of Halloween
Halloween has ancient origins in the United Kingdom. It seems to be a version of the ancient Celtic holiday called "Samhain" (sow' an) celebrating the end of harvest and the beginning of the new year. The Druids, a Celtic religious group, brought in Saman, the Lord of the Dead. They believed that the dead were allowed to wander on earth in search of living bodies to take over and turn into evil witches. People made themselves and their homes as undesirable as possible to keep the spirits away by wearing costumes, masks, being loud and obnoxious, and keeping their homes cold and dark.
Prodolzhenie zdes' Извините за транслит