The Christian feast of All Saints was assigned to November 1st. The day honored every Christian saint, especially those that did not otherwise have a special day devoted to them. This feast day was meant to substitute for Samhain, to draw the devotion of the Celtic peoples, and, finally, to replace it forever. That did not happen, but the traditional Celtic deities diminished in status, becoming fairies or leprechauns of more recent traditions.
The old beliefs associated with Samhain never died out entirely. The powerful symbolism of the traveling dead was too strong, and perhaps too basic to the human psyche, to be satisfied with the new, more abstract Catholic feast honoring saints. Recognizing that something that would subsume the original energy of Samhain was necessary, the church tried again to supplant it with a Christian feast day in the 9th century. This time it established November 2nd as All Souls Day--a day when the living prayed for the souls of all the dead. But, once again, the practice of retaining traditional customs while attempting to redefine them had a sustaining effect: the traditional beliefs and customs lived on, in new guises.
All Saints Day, otherwise known as All Hallows (hallowed means sanctified or holy), continued the ancient Celtic traditions. The evening prior to the day was the time of the most intense activity, both human and supernatural. People continued to celebrate All Hallows Eve as a time of the wandering dead, but the supernatural beings were now thought to be evil. The folk continued to propitiate those spirits (and their masked impersonators) by setting out gifts of food and drink. Subsequently, All Hallows Eve became Hallow Evening, which became Hallowe'en--an ancient Celtic, pre-Christian New Year's Day in contemporary dress.
Many supernatural creatures became associated with All Hallows. In Ireland fairies were numbered among the legendary creatures who roamed on Halloween. An old folk ballad called "Allison Gross" tells the story of how the fairy queen saved a man from a witch's spell on Halloween.
O Allison Gross, that lives in yon tower
the ugliest witch int he North Country...
She's turned me into an ugly worm
and gard me toddle around a tree...
But as it fell out last Hallow even
When the seely [fairy] court was riding by,
the Queen lighted down on a gowany bank
Not far from the tree where I wont to lie...
She's change me again to my own proper shape
And I no more toddle about the tree.
In old England cakes were made for the wandering souls, and people went "a' soulin'" for these "soul cakes." Halloween, a time of magic, also became a day of divination, with a host of magical beliefs: for instance, if persons hold a mirror on Halloween and walk backwards down the stairs to the basement, the face that appears in the mirror will be their next lover.
Library of Congress