Halloween: The Fantasy and Folklore of All Hallows
Author: Jack Santino
Halloween had its beginnings in an ancient, pre-Christian Celtic festival of the dead. The Celtic peoples, who were once found all over Europe, divided the year by four major holidays. According to their calendar, the year began on a day corresponding to November 1st on our present calendar. The date marked the beginning of winter. Since they were pastoral people, it was a time when cattle and sheep had to be moved to closer pastures and all livestock had to be secured for the winter months. Crops were harvested and stored. The date marked both an ending and a beginning in an eternal cycle.
Samhain became the Halloween we are familiar with when Christian missionaries attempted to change the religious practices of the Celtic people. In the early centuries of the first millennium A.D., before missionaries such as St. Patrick and St. Columcille converted them to Christianity, the Celts practiced an elaborate religion through their priestly caste, the Druids, who were priests, poets, scientists and scholars all at once. As religious leaders, ritual specialists, and bearers of learning, the Druids were not unlike the very missionaries and monks who were to Christianize their people and brand them evil devil worshippers.
Read the rest of the article on the Library of Congress site
you'll also find A Selected Bibliography on Halloween and Related Topics