Halloween originated from the ancient Celtic festival of Samhain, celebrated on November 1st. Celts believed the night before, October 31st, was when the ghosts of the dead returned and mingled with the living. To avoid recognition, people wore costumes and masks. As Christianity spread, the holiday was transformed into All Saints' Day. Over time, traditions evolved to include carving jack-o-lanterns from pumpkins and children going door-to-door collecting treats. Irish immigration in the 1800s helped popularize Halloween in America. While Halloween has pagan roots, the Bible warns against practices that could involve darkness or the occult.