Today, it's a chance for adults and children to act out their fantasies in costumes.

It has roots in the ancient Celtic celebration, Samhain, where people carved scary faces into hallowed turnips to ward off evil spirits. And Pomona, a Roman fall festival in which the apple, and later apple bobbing, was an important symbol.

When Christianity spread in the Middle Ages, the Catholic Church viewed Samhain and Pomona as paganism. The church created three holidays, collectively called Hallowmas, to supplant the festivals: All Hallows Eve, an evening of preparation, Oct. 31; All Saints' Day, to recognize canonized saints, Nov. 1; and All Soul's Day, for non-sainted people who died in the past year, Nov. 2.

Eventually, All Hallow's Eve and its revelry became the most popular holiday. It was eventually shortened to Hallowe'en, now Halloween.